Diesel engine and gasoline efficiency comparison. Diesel and Electric cars in Germany

ICE operating according to the Otto cycle: 1 - intake stroke of the fuel-air mixture; 2 - compression and ignition stroke of the mixture; 3 — expansion stroke of the burning mixture; 4 - exhaust cycle of combustion products Scheme: two-stroke internal combustion engine with a resonator pipe

four-stroke in-line four-cylinder internal combustion engine
Internal combustion engine (ICE)

- an engine in which fuel burns directly in the working chamber (
inside
) of the engine. The internal combustion engine converts thermal energy from fuel combustion into mechanical work.

Compared to internal combustion engines:

• has no additional heat transfer elements - the fuel itself forms the working fluid;
• more compact, since it does not have a number of additional units;
• easier;
• more economical;
• consumes fuel that has very strictly specified parameters (volatility, vapor flash point, density, calorific value, octane or cetane number), since the performance of the internal combustion engine depends on these properties.

Content

• 1 History of creation
• 2 Types of internal combustion engines
• 3 Fuel octane number
• 4 Ratio of cylinder diameter to stroke
• 5 Gasoline 5.1 Gasoline carburetor
• 5.2 Gasoline injection

Asynchronous motor and stirling

Today, asynchronous machines are presented on the market, most of which are electric. An asynchronous mechanism converts electrical energy into mechanical energy.

Their main advantages:

• ease of manufacture and relatively low cost;
• high reliability;
• operating costs are low.

The efficiency formula is calculated as follows: η = P2 / P1 = (P1 - (Pob - Ps - Pmx - Pd)) / P1, where Rob = Pob1 + Rob2 - the total losses in the windings of an asynchronous motor. For most modern mechanisms of this type, the coefficient reaches 80 - 90%.

Another internal combustion engine that can be powered by any heat source is the Stirling engine.

It should be noted that such mechanisms are used on spacecraft and modern submarines.

It operates at any temperature, does not require additional systems to start, and their efficiency is 50-70 higher than that of conventional engines.

History of creation

In 1807, the French-Swiss inventor François Isaac de Rivaz built the first piston engine, often called the de Rivaz engine. The engine ran on hydrogen gas, featuring design elements that have since been incorporated into subsequent internal combustion engine prototypes: a piston group and spark ignition. There was no crank mechanism in the engine design yet.

Lenoir gas engine, 1860.

The first practical two-stroke gas internal combustion engine was designed by the French mechanic Etienne Lenoir in 1860. Power was 8.8 kW (11.97 hp). The engine was a single-cylinder, horizontal, double-acting machine, running on a mixture of air and lighting gas with electric spark ignition from an external source. A crank mechanism appeared in the engine design. The engine efficiency did not exceed 4.65%. Despite its shortcomings, the Lenoir engine gained some popularity. Used as a boat engine.

Having become acquainted with the Lenoir engine, in the fall of 1860, the outstanding German designer Nikolaus August Otto and his brother built a copy of the Lenoir gas engine and in January 1861 submitted an application for a patent for a liquid fuel engine based on the Lenoir gas engine to the Prussian Ministry of Commerce, but the application was rejected. In 1863 he created a two-stroke atmospheric internal combustion engine. The engine had a vertical cylinder arrangement, open flame ignition and an efficiency of up to 15%. Replaced the Lenoir engine.

Four-stroke Otto engine from 1876.

In 1876, Nikolaus August Otto built a more advanced four-stroke gas internal combustion engine.

In the 1880s, Ogneslav Stepanovich Kostovich built the first gasoline carburetor engine in Russia.

Daimler motorcycle with internal combustion engine 1885

In 1885, German engineers Gottlieb Daimler and Wilhelm Maybach developed a lightweight gasoline carburetor engine. Daimler and Maybach used it to create the first motorcycle in 1885, and in 1886 the first automobile.

German engineer Rudolf Diesel sought to improve the efficiency of the internal combustion engine and in 1897 proposed a compression ignition engine. At Emmanuel Ludvigovich Nobel in St. Petersburg in 1898-1899, Gustav Vasilyevich Trinkler improved this engine by using compressorless fuel atomization, which made it possible to use oil as a fuel. As a result, the compressorless, high-compression, self-ignition internal combustion engine has become the most economical stationary heat engine. In 1899, the first diesel engine was built in Russia and mass production of diesel engines began. This first diesel had a power of 20 hp. s., one cylinder with a diameter of 260 mm, a piston stroke of 410 mm and a rotation speed of 180 rpm. In Europe, the diesel engine, improved by Gustav Vasilyevich Trinkler, was called “Russian diesel” or “Trinkler-motor”. At the World Exhibition in Paris in 1900, the Diesel engine received the main prize. In 1902, the Kolomna Plant bought a license for the production of diesel engines from Emmanuel Ludvigovich Nobel and soon established mass production.

In 1908, the chief engineer of the Kolomna plant, R. A. Koreivo, built and patented in France a two-stroke diesel engine with counter-moving pistons and two crankshafts. Koreivo diesel engines began to be widely used on motor ships of the Kolomensky Plant. They were also produced at Nobel factories.

In 1896, Charles W. Hart and Charles Parr developed a two-cylinder gasoline engine. In 1903, their company built 15 tractors. Their six-ton ​​#3 is the oldest internal combustion engine tractor in the United States and is housed in the Smithsonian National Museum of American History in Washington, DC. The two-cylinder petrol engine had a completely unreliable ignition system and a power of 30 hp. With. at idle and 18 l. With. under load[1].

Dan Albon with his prototype Ivel farm tractor

The first practical tractor powered by an internal combustion engine was Dan Alborn's 1902 American lvel three-wheel tractor. About 500 of these light and powerful machines were built.

Engine used by the Wright brothers in 1910

In 1903, the first airplane was flown by brothers Orville and Wilbur Wright. The plane's engine was built by mechanic Charlie Taylor. The main parts of the engine are made of aluminum. The Wright-Taylor engine was a primitive version of the gasoline injection engine.

On the world's first motor ship, the oil tanker barge "Vandal", built in 1903 in Russia on Sormovsky, three four-stroke Diesel engines with a capacity of 120 hp were installed. With. every. In 1904, the motor ship Sarmat was built.

In 1924, according to the design of Yakov Modestovich Gakkel, the diesel locomotive YuE2 (ShchEL1) was created at the Baltic Shipyard in Leningrad.

Almost simultaneously in Germany, by order of the USSR and according to the project of Professor Yu. V. Lomonosov, on the personal instructions of V. I. Lenin, in 1924, a diesel locomotive Eel2 (originally Yue001) was built at the German plant Esslingen (formerly Kessler) near Stuttgart.

Types of internal combustion engines

Piston internal combustion engine

Rotary internal combustion engine

Gas turbine internal combustion engine

• Piston engines - the combustion chamber is a cylinder, the reciprocating movement of the piston is converted into shaft rotation using a crank mechanism.

• Gas turbine - energy conversion is carried out by a rotor with wedge-shaped blades.

• Rotary piston engines - in them, energy conversion is carried out due to the rotation of a special profile rotor by working gases (Wankel engine).

ICEs are classified:

• by purpose - transport, stationary and special.
• by type of fuel used - light liquid (gasoline, gas), heavy liquid (diesel fuel, marine fuel oil).
• according to the method of formation of the combustible mixture - external (carburetor) and internal (in the internal combustion engine cylinder).
• by volume of working cavities and weight-dimensional characteristics - light, medium, heavy, special.

In addition to the above classification criteria common to all internal combustion engines, there are criteria by which individual types of engines are classified. Thus, piston engines can be classified by the number and arrangement of cylinders, crankshafts and camshafts, by the type of cooling, by the presence or absence of a crosshead, supercharging (and by the type of supercharging), by the method of mixture formation and by the type of ignition, by the number of carburetors, by the type of gas distribution mechanism, by the direction and frequency of rotation of the crankshaft, by the ratio of the cylinder diameter to the piston stroke, by the degree of speed (average piston speed).

collection of problems in thermal engineering / CHAPTER 5

CHAPTER
5

INTERNAL COMBUSTION
ENGINES § 5.1. PARAMETERS CHARACTERIZING ENGINE OPERATION

Average indicator pressure and indicator power.

By average indicator pressure
p i
we mean such a conditional constant pressure that, acting on the piston during one working stroke, does work equal to the indicator work of the gases in the cylinder during the working cycle.

According to the definition, the average indicator pressure (Pa) is equal to the ratio of the indicator work L i

gases per cycle per unit of working volume
V h
of the cylinder, i.e.

. (5.1)

If you have an indicator diagram taken from the engine (Fig. 5.1), the average indicator pressure can be determined by the formula

. (5.2)

where F

— useful area of ​​the indicator diagram, m2;
l
is the length of the indicator diagram, m;
t
is the pressure scale of the indicator diagram, Pa/m.

The average indicator pressure at full load for four-stroke carburetor engines is 8·105...12·105 Pa, for four-stroke diesel engines - 7.5·105...10·105 Pa, for two-stroke diesel engines - 6·105...9·105 Pa.

Indicator power N i

(kW) of an engine is the work done by the gases in the engine cylinders per unit time, i.e.

, (5.3)

where p i

— average indicator pressure, Pa;
V h
—cylinder working volume, m3;
n
— crankshaft rotation speed, r/s;
τ
— engine stroke (
τ
=4 — for four-stroke engines and
τ
=2 — for two-stroke);
i
is the number of cylinders.

Cylinder displacement (m3)

V h = nD 2 S

/4, (5.4)

where D

— cylinder diameter, m;
S
— piston stroke, m.

If the compression ratio e of the engine and the volume V c

combustion chamber, then the working volume
V h
of the cylinder can be determined by the formula

V h

=(

-1)
V c
, (5.5)

Where 

- compression ratio equal to the ratio of the total volume
V a
of the cylinder to the volume
V c
of the combustion chamber, i.e.

.

Effective engine power and mean effective pressure. Effective power N e

is the power removed from the engine crankshaft to produce useful work.

Effective power is less than indicator power N i

by the amount of power
N M
mechanical losses, i.e.

N e = N i - N M .

(5.6) .

Mechanical losses in the engine are estimated by mechanical efficiency η m

which is the ratio of effective power to indicator power:

.

(5.7)

For modern engines, mechanical efficiency is 0.72...0.9. Knowing the mechanical efficiency, you can determine the effective power

N e = η m N i .

(5.8 )

Effective power N e

(kW) of the engine, similarly to the indicated power, can be expressed in terms of the mean effective pressure:

. (5.9 )

Average effective pressure p e

is equal to the difference between the average indicator pressure
p i
and the average pressure
p m of
mechanical losses:

p e = p i - p m

. (5.10)

Knowing the mechanical efficiency, the average effective pressure (Pa) can be determined:

r e = η m r i .

(5.11)

The average effective pressure at maximum power for four-stroke carburetor engines is 6.5 105...9.5 105 Pa, for four-stroke diesel engines - 6 105...8 105 Pa, for two-stroke diesel engines - 5 105...7.5 105 Pa.

Liter engine power.

Liter engine power N
l , (
kW/m3) is the ratio of effective power N
e to
engine displacement iV
h :

. (5.12)

Indicated efficiency and specific indicated fuel consumption.

The efficiency of the actual operating cycle of the engine is assessed by indicator efficiency
η i
and specific indicator fuel consumption
b i .
Indicator efficiency η i

evaluates the degree of heat utilization in the actual cycle, taking into account all heat losses and represents the ratio of heat equivalent to useful indicator work to all heat expended:

. (5.13)

where N i

— indicator power, kW;
B
— fuel consumption, kg/s;
Q
is the lower heating value of fuel, kJ/kg.

Specific indicator fuel consumption b i ,

[kg/(kWh)] is the ratio of fuel consumption
B
to indicated power
N i .
b i = B

·3600/
N i .
(5.14)

Values ​​of η i

and
b i
for engines when operating at nominal mode are given in table. 5.1.

Table 5.1

Effective efficiency and specific effective fuel consumption.

The efficiency of engine operation as a whole is assessed by effective efficiency
η e
and specific effective fuel consumption
b e .
Effective efficiency η e

evaluates the degree of use of fuel heat, taking into account all types of losses (both thermal and mechanical) and represents the ratio of heat equivalent to useful effective work to all heat expended:

. (5.15)

If indicator efficiency and mechanical efficiency are known, then

η e =η i η m

. (5.16)

Specific effective fuel consumption b e

[kg/(kWh)] is the ratio of fuel consumption
B
to effective power
N e :
b e = B

·3600
/ N e .
(5.17)

Values ​​of η e

and
b e
for engines when operating at nominal mode are given in table. 5.1.

Flow rate (kg/s) of air passing through the engine:

M in =

2
V h η V niρ in
/
τ
, (5.18)

where V h

— cylinder working volume, m3;
η V
— cylinder filling coefficient;
n
— crankshaft rotation speed, r/s;
i
— number of cylinders;
ρ in
— air density, kg/m3;
m
is the engine stroke.

Problem 5.1.

Determine the indicator and effective power of an eight-cylinder four-stroke carburetor engine if the average indicator pressure
p i =
7.5 105 Pa, cylinder diameter
D
= 0.1 m, piston stroke
S
= 0.095 m, crankshaft speed
n
= 3000 rpm and mechanical efficiency
η m
=0.8.

Answer:
N i
=112.5 kW;
N e
=90 kW.

Problem 5.2.

Determine the effective power and specific effective fuel consumption of an eight-cylinder four-stroke diesel engine, if the average indicator pressure
p i
= 7.5 105 Pa, compression ratio

= 16.5, combustion chamber volume
V c
= 12 10-5 m3, angular velocity crankshaft rotation
w
=220 rad/s, mechanical efficiency
η m
=0.8 and fuel consumption
B
=1.02·10-2 kg/s.

Solution

: The average effective pressure is determined by formula (5.11):

r e = η m r i

=7.5·105·0.8=6·105 Pa.

The working volume of the cylinder, according to formula (5.5),

V h

=(

-1)
V c
=(16.5-1)12·10-5=18.6·10-4 m3.

Engine speed

n

=
w
/(2

)=220/(2·3.14)=35 r/s.

Effective engine power, according to formula (5.9),

=156 kW.

Specific effective fuel consumption, according to formula (5.17),

b e =B

·3600
/N e =
1.02·10-2·3600/156=0.235 kg/(kWh).

Problem 5.3.

Determine the specific effective fuel consumption of a six-cylinder four-stroke diesel engine if the average effective pressure
p e
= 7.2 105 Pa, the total cylinder volume
V a
= 1.9 10-4 m3, the combustion chamber volume
V c
= 6.9 10 -5 m3, crankshaft rotation speed
p
= 37 r/s and fuel consumption
B =
3.8·10-3 kg/s.

Answer:
b e =
0.238 kg/(kWh).

Problem 5.4.

Determine the indicator power and average indicator pressure of a four-cylinder four-stroke diesel engine, if the effective power
N e
= 100 kW, the angular speed of rotation of the crankshaft
w
= 157 rad/s, the compression ratio

= 15, the volume of the combustion chamber
V c
= 2.5 10 -4 m3 and mechanical efficiency
η m
=0.84.

Answer: N i

=119 kW;
p i
=6.8·105 Pa.

Problem 5.5.

Determine the indicator power and specific indicator fuel consumption of a six-cylinder four-stroke diesel engine, if the average effective pressure
p e
= 6.2 105 Pa, cylinder diameter
D
= 0.11 m, piston stroke
S
= 0.14 m, average piston speed
c t
=8.4 m/s, fuel consumption
B
=5.53·10-3 kg/s and mechanical efficiency
η m
=0.82.

Answer:
N i
=90.5 kW;
b i
=0.220 kg/(kWh).

Problem 5.6.

Determine the cylinder diameter and piston stroke of a four-cylinder four-stroke diesel engine, if the effective power
N e
= 80 kW, the average effective pressure p
e =
105 Pa, the crankshaft speed n

1800
t =
, 6 m/s.

Answer:
D
=0.135 m;
B
=0.16 m.

Problem 5.7.

Determine the power of mechanical losses of an eight-cylinder four-stroke carburetor engine if the average indicator pressure
p e
= 1.5 105 Pa, cylinder diameter
D
= 0.1 m, piston stroke
S
= 0.095 m, crankshaft rotation speed
n
= 50 rpm and mechanical efficiency
η m
=0.8.

Answer:
N M
=22.4 kW.

Problem 5.8.

Determine the indicator power and mechanical loss power of a six-cylinder two-stroke diesel engine, if the average effective pressure
p e
= 6.36 105 Pa, compression ratio

= 16, combustion chamber volume
V c
= 7.8 10-5 m3, crankshaft rotation speed shaft
n
=35 r/s and mechanical efficiency
η m
=0.84.

Answer:
N i
=186 kW;
N M
=29.8 kW.

Problem 5.9.

Determine the average indicator pressure and the average pressure of mechanical losses of an eight-cylinder four-stroke carburetor engine, if the effective power N
e =
145 kW, cylinder diameter D
=
0.1 m, piston stroke V
h =
0.09 m, average piston speed with
t =
12.0
η m
=0.8.

Answer:
p i
=9.6·105 Pa;
p m
=1.92·105 Pa.

Problem 5.10.

Determine the effective power and specific effective fuel consumption of an eight-cylinder four-stroke carburetor engine if the indicator gas work per cycle is
L i
=649 J, cylinder diameter
D
=0.1 m, piston stroke
S
=0.095 m, average piston speed
with m
=9.5 m/s, mechanical efficiency
η m
=0.85 and fuel consumption
B
=9.1·10-3 kg/s.

Answer:
N e =
110.5 kW;
b e
=0.316 kg/(kWh).

Problem 5.11.

Determine the specific indicator and effective fuel consumption of a four-cylinder four-stroke diesel engine, if the average indicator pressure
p i
=6.8·105 Pa, compression ratio

=15, total cylinder volume
V a
=37.5·10-4 m3, angular velocity crankshaft
w
=157 rad/s, mechanical efficiency
η m
=0.84 and fuel consumption
B
=5.95·10-3 kg/s.

Answer:
b i
=0.180 kg/(kWh);
b e =
0.214 kg/(kWh).

Problem 5.12.

Determine the effective power and mechanical loss power of a six-cylinder four-stroke diesel engine, if the average effective pressure
p e =
5.4 105 Pa, cylinder diameter
D =
0.108 m, piston stroke
S
= 0.12 m, average piston speed
with t
= 8, 4 m/s and mechanical efficiency
η m
=0.78.

Answer:
N e
=62.4 kW;
N M
=17.6 kW.

Problem 5.13.

Determine the average indicator pressure and indicator power of a six-cylinder four-stroke diesel engine if the cylinder diameter
D
= 0.15 m, piston stroke
S
= 0.18 m, crankshaft speed
n
= 1500 rpm.
By indicating the engine, an indicator diagram was obtained with a useful area F
=l.95·10-3 m2, length
l
=0.15 m at a pressure scale
t =
0.6·108 Pa/m.

Answer: p i

=7.8·105 Pa,
N i =
186 kW.

Problem
5.14.
Determine the specific indicator fuel consumption of a six-cylinder four-stroke carburetor engine if the cylinder diameter
D =
0.082 m, piston stroke
S
= 0.11 m, crankshaft speed
n
= 2800 rpm, fuel consumption
B
= 4.5 10-3 kg/ With.
By indicating the engine, an indicator diagram was obtained with a useful area F
= 1.6·10-3 m2, length
l
= 0.2 m at a pressure scale
m
= 1108 Pa/m.

Solution

: The average indicator pressure is determined by formula (5.2):

p i = Fm / l =

1.6·10-3·1·108/0.2=8·105 Pa.

The working volume of the cylinder, according to formula (5.4),

V h

=
 D 2 S
/4=3.14·0.0822·0.11/4=5.8·104 m3.

Indicated engine power, according to formula (5.3),

=65 kW.

Specific indicator fuel consumption, according to formula (5.14),

b i =B

·3600/
N i =
4.5·10-3·3600/65=0.249 kg/(kWh).

Problem 5.15.

Determine the indicator power and mechanical loss power of a four-cylinder four-stroke diesel engine, if the compression ratio

=17, the total cylinder volume
V a
=11.9·10-4 m3, the angular speed of the crankshaft
w
=157 rad/s and the mechanical efficiency
η m
=0.81.
By indicating the engine, an indicator diagram was obtained with a useful area F =
1.8 10-3 m2, length
l
= 0.2 m at a pressure scale
t
= 0.8 108 Pa/m.

Answer:
N i
=40.3 kW;
N M
=7.7 kW.

Problem 5.16.

Determine the average effective pressure and the average pressure of mechanical losses of a two-cylinder four-stroke diesel engine, if the effective power
N e
= 18 kW, cylinder diameter
D
= 0.105 m, piston stroke
S
= 0.12 m, crankshaft speed
n
= 30 rpm and mechanical efficiency
η m
=0.78.

Answer: r e =

5.77·105 Pa;
p m =
1.63·105 Pa.

Problem 5.17.

Determine the effective power and mechanical efficiency of a six-cylinder four-stroke diesel engine if the average effective pressure
p e
= 7.2 105 Pa, the total cylinder volume
V a
= 7.9 10-4 m3, the combustion chamber volume
V c
= 6.9 10-5 m3, crankshaft rotation speed
n
=37 r/s and mechanical loss power
N M
=14.4 kW.

Answer:
N e
=57.6 kW;
η m
=0.8.

Problem 5.18.

Determine the average piston speed and compression ratio of a four-cylinder four-stroke carburetor engine, if the effective power
N e
= 51.5 kW, the average effective pressure
p e =
6.45 105 Pa, piston stroke
S
= 0.092 m, crankshaft speed
n
= 4000 rpm and combustion chamber volume
V c =
1·10-4 m3.

Answer:
with m
=12.3 m/s;

=7.0.

Problem 5.19.

Determine the angular speed of rotation of the crankshaft and the compression ratio of a six-cylinder four-stroke carburetor engine, if the effective power
N e =
66 kW, the average effective pressure
p e =
6.5 105 Pa, the crankshaft speed
n
= 60 rpm and the total volume of the cylinder
V a
=6.63·10-4 m3.

Answer:
w=
377 rad/s;

=6.7.

Problem 5.20.

Determine the indicator power and mechanical efficiency of an eight-cylinder four-stroke carburetor engine if the average indicator pressure
p e =
7.5 105 Pa, cylinder diameter
D
= 0.1 m, piston stroke
S
= 0.095 m3 average piston speed
with t
= 9.5 m /s and mechanical loss power
N M
=23.5 kW.

Answer:
N i =
111.8 kW;
η m
=0.79.

Problem 5.21.

Determine the displacement and specific effective fuel consumption of a six-cylinder four-stroke carburetor engine, if the effective power
N e
= 52 kW, the average effective pressure
p e =
6.4 105 Pa, the angular speed of rotation of the crankshaft
w
= 314 rad/s and the fuel consumption
B
= 3.8·10-3 kg/s.

Answer:
iV h =
32.5·10-4 m3;
b e
=0.263 kg/(kWh).

Problem 5.22.

Determine the fuel consumption of a four-cylinder four-stroke diesel engine if the average indicator pressure
p i
=6.8 105 Pa, crankshaft rotation speed
n
=25 r/s, compression ratio

=15, combustion chamber volume
V c
=2.5 10 -4 m3, mechanical efficiency
η m
=0.84 and specific effective fuel consumption
b e =
0.180 kg/(kWh).

Answer: B

=5·10-3 kg/s.

Problem 5.23.

Determine the fuel consumption of a six-cylinder four-stroke carburetor engine if the average indicator pressure
p i
= 8·105 Pa, cylinder diameter
D =
0.082 m, piston stroke
S
average
piston speed
t = 9.9 m/s, mechanical efficiency
η m
=0.85 and specific effective fuel consumption b
e =
0.276

Answer:
B
=4.08·10-3 kg/s.

Problem 5.24.

Determine the liter power and specific indicator fuel consumption of an eight-cylinder four-stroke carburetor engine, if the average indicator pressure p
i =
·105 Pa, cylinder diameter D
=
0.12 m, piston stroke S
=
0.1 m, angular speed of crankshaft rotation w

=
η m
=0.8 and fuel consumption
B
=16·10-3 kg/s.

Solution

: The working volume of the cylinder is determined by formula (5.4):

V h =nD 2 S

/4=3.14·0.122·0.1/4=11.3·104 m3.

Engine speed

n

=
w
/(2

)=377/(2·3.14)=60 r/s.

Indicated engine power, according to formula (5.3),

=217 kW.

Effective engine power, according to formula (5.8),

N e = η m N i =

217·0.8=173.6 kW.

Liter engine power, according to formula (5.12),

=19200 kW/m3.

Specific indicator fuel consumption, according to formula (5.14),

b i =B

·3600/
N i =
16·10-3·3600/217=0.265 kg/(kWh).

Problem 5.25.

Determine the liter power of a six-cylinder four-stroke diesel engine if the average effective pressure
p e
= 1·105 Pa, crankshaft speed
n =
35 r/s, compression ratio

= 14.5 and combustion chamber volume
V s
= 22·10-5 m3.

Answer:
N l =
12250 kW/m3.

Problem 5.26.

Determine the indicated power and fuel consumption of an eight-cylinder carburetor engine if the average effective pressure
p e =
6.56 105 Pa, cylinder diameter D
=
0.12 m, piston stroke S
=
0.1 m, crankshaft rotation speed n
=
70 rpm /s, mechanical efficiency
η m
=0.82 and specific indicator fuel consumption
b i =
0.265 kg/(kWh).

Answer:
N i
= 253 kW;
B=
18.6·10-2 kg/s.

Problem 5.27.

Determine the crankshaft rotation speed and specific effective fuel consumption of a four-cylinder four-stroke diesel engine, if the effective power N
e =
109 kW, the average effective pressure p
e =
5.6
=
14, the combustion chamber volume V
c =
2 .5·10-4 m3 and fuel consumption
B
=6.5·10-3 kg/s.

Answer: p=

30 rps;
b e
=0.215 kg/(kWh).

Problem 5.28.

Determine the effective efficiency of a six-cylinder four-stroke carburetor engine if the average effective pressure
p e =
6.2 105 Pa, the lower heating value of fuel
Q
= 44,000 kJ/kg, cylinder diameter
D =
0.092 m, piston stroke
S
= 0.082 m, average speed piston
with t
= 8.2 m/s and fuel consumption
B
= 4.4·10-3 kg/s.

Solution

: The working volume of the cylinder is determined by formula (5.4):

V h =nD 2 S

/4=3.14·0.0922·0.082/4=5.45·10-4 m3.

Engine speed

n

=
c m
/(2
S
)=8.2/(2·0.082)=50 r/s.

Effective engine power, according to formula (5.9),

=50.7 kW.

Effective efficiency, according to formula (5.15),

=0,26.

Problem 5.29.

Determine the indicator and mechanical efficiency of a four-cylinder four-stroke diesel engine, if the average indicator pressure
p i =
6.8 105 Pa, the lower heat of combustion of the fuel
Q
= 41800 kJ/kg, the angular velocity of the crankshaft
w
= 157 rad/s, the compression ratio

= 15, combustion chamber volume
V c
=2.5·10-4 m3, fuel consumption
B
=6·10-3 kg/s and effective efficiency
η e
=0.4.

Answer:
η i
=0.476;
η m
=0.84.

Problem 5.30.

Determine the indicator efficiency of a six-cylinder two-stroke diesel engine if the average effective pressure
p e =
6.36 105 Pa, lower heating value of fuel
Q
= 42000 kJ/kg, compression ratio

= 16, combustion chamber volume V
s =
7.8 10 -5 m3, crankshaft rotation speed
n
=2100 rpm, fuel consumption
B
=1.03·10-2 kg/s and mechanical loss power
N M =
29.8 kW.

Answer:
η i
=0.43.

Problem 5.31.

Determine the indicator and effective efficiency of a four-cylinder four-stroke diesel engine, if the compression ratio

=17, the total volume of the cylinder
V a
=11.9·10-4 m3, the angular speed of rotation of the crankshaft
w
=157 rad/s, the lower heat of combustion of the fuel
Q
= 42600 kJ/kg, fuel consumption
B
=2.2·10-3 kg/s and mechanical efficiency
η m
=0.81.
By indicating the engine, an indicator diagram was obtained with a useful area F
= 1.9·10-3 m2, length
l
= 0.19 m, with a pressure scale
m
= 0.72·108 Pa/m.

Answer:
η i
=0.43;
η e
=0.35.

Problem 5.32.

Determine the fuel consumption for an eight-cylinder four-stroke carburetor engine if the average effective pressure
p e =
7 105 Pa, the total cylinder volume
V a
= 7.9 10-4 m3, the combustion chamber volume
V c
= 7.0 10-5 m3, crankshaft rotation speed
n
=53 r/s, lower heating value of fuel
Q
=46000 kJ/kg and effective efficiency
η e
=0.28.

Answer:
B
=8.3·10-3 kg/s.

Problem 5.33.

Determine the fuel consumption for a six-cylinder four-stroke diesel engine if the average indicator pressure
p i =
9·105 Pa, the total cylinder volume
V a
=7.9·10-4 m3, the combustion chamber volume
V c
=6.9·10-5 m3 , crankshaft rotation speed
p
= 2220 rpm, lower heating value of fuel
Q
= 42800 kJ/kg, effective efficiency
η e
= 0.35 and mechanical efficiency
η m
= 0.84.

Solution

: Cylinder displacement

V h = V a - V c

=1.9·10-4-6.9·10-5=7.2·10-4 m3.

The indicator efficiency is determined from formula (5.16):

η i =η e / η m

=0,35/0,84=0,44.

Indicated engine power, according to formula (5.3),

=72 kW.

Fuel consumption, according to formula (5.13),

=

3.82·10-3 kg/s.

Problem 5.34.

Determine the fuel economy as a percentage, which is obtained by replacing a carburetor engine with a diesel engine of average indicated power
N i
= 148 kW, if the indicated efficiency of a carburetor engine
is η i 1 =
0.34, of a diesel engine -
η i 2 =
0.45.
The lowest calorific value of gasoline is Q
= 43500 kJ/kg, diesel fuel
Q =
42600 kJ/kg.

Fuel octane number

Energy is transferred to the engine crankshaft from the expanding gases during the power stroke. Compressing the fuel-air mixture to the volume of the combustion chamber improves engine efficiency and increases its efficiency, but increasing the compression ratio also increases the heating of the working mixture caused by compression according to Charles's law.

If the fuel is flammable, the flash occurs before the piston reaches TDC. This, in turn, will cause the piston to turn the crankshaft in the opposite direction - this phenomenon is called backfire.

Octane number is a measure of the percentage of isooctane in a heptane-octane mixture and reflects the fuel's ability to resist self-ignition when exposed to temperature.

Higher octane fuels allow a high compression engine to operate without the tendency to self-ignite or detonate and therefore have a higher compression ratio and higher efficiency.

The operation of diesel engines is ensured by self-ignition from compression in the cylinder of clean air or a lean gas-air mixture incapable of spontaneous combustion (gas diesel) and the absence of fuel in the charge until the last moment.

Ratio of cylinder diameter to stroke

One of the fundamental design parameters of an internal combustion engine is the ratio of the piston stroke to the cylinder diameter (or vice versa). For faster gasoline engines, this ratio is close to 1; on diesel engines, the piston stroke, as a rule, is larger than the cylinder diameter, the larger the engine. The optimal ratio from the point of view of gas dynamics and piston cooling is 1: 1. The longer the piston stroke, the greater the torque the engine develops and the lower its operating speed range. On the contrary, the larger the cylinder diameter, the higher the engine operating speed and the lower its torque at low speeds. As a rule, short-stroke internal combustion engines (especially racing ones) have more torque per unit of displacement, but at relatively high speeds (more than 5000 rpm). With a larger cylinder/piston diameter, it is more difficult to ensure proper heat removal from the bottom of the piston due to its large linear dimensions, but at high operating speeds, the speed of the piston in the cylinder does not exceed the speed of the longer-stroke piston at its operating speeds.

Which engine has the highest efficiency?

Now I want to talk about gasoline and diesel options, and find out which of them is the most efficient.

To put it in simple language and without getting into the weeds of technical terms, if you compare the two efficiency factors, the more efficient of them is, of course, diesel and here’s why:

1) A gasoline engine converts only 25% of energy into mechanical energy, but a diesel engine converts about 40%.

2) If you equip a diesel type with turbocharging, you can achieve an efficiency of 50-53%, and this is very significant.

So why is it so effective? It's simple - despite the similar type of work (both are internal combustion units), diesel does its job much more efficiently. It has greater compression, and the fuel ignites using a different principle. It heats up less, which means there is a saving on cooling, it has fewer valves (saving on friction), and it also does not have the usual ignition coils and spark plugs, which means it does not require additional energy costs from the generator. It operates at lower speeds, there is no need to frantically spin the crankshaft - all this makes the diesel version a champion in terms of efficiency.

Gasoline

Gasoline carburetor

Additional information: Carburetor

A mixture of fuel and air is prepared in the carburetor, then the mixture is fed into the cylinder, compressed, and then ignited using a spark that jumps between the electrodes of the spark plug. The main characteristic feature of the fuel-air mixture in this case is homogeneity.

Gasoline injection

Additional information: Fuel injection system

There is also a method of mixture formation by injecting gasoline into the intake manifold or directly into the cylinder using spray nozzles (injector). There are single-point (mono-injection) and distributed injection systems of various mechanical and electronic systems. In mechanical injection systems, fuel dosage is carried out by a plunger-lever mechanism with the ability to electronically adjust the mixture composition. In electronic systems, mixture formation is carried out using an electronic control unit (ECU) that controls electric gasoline injectors.

Diesel, compression ignition

The diesel engine is characterized by igniting the fuel without the use of a spark plug. A portion of fuel is injected into the air heated in the cylinder from adiabatic compression (to a temperature exceeding the ignition temperature of the fuel) through a nozzle. During the injection of the fuel mixture, it is atomized, and then combustion centers appear around individual droplets of the fuel mixture; as the fuel mixture is injected, it burns in the form of a torch. Since diesel engines are not subject to the phenomenon of detonation characteristic of engines with forced ignition, they can use higher compression ratios (up to 26), which, in combination with long combustion, providing constant pressure of the working fluid, has a beneficial effect on the efficiency of this type of engine , which can exceed 50% in the case of large marine engines.

Diesel engines are slower and have higher shaft torque. Also, some large diesel engines are adapted to run on heavy fuels, such as fuel oil. Starting of large diesel engines is carried out, as a rule, due to a pneumatic circuit with a supply of compressed air, or, in the case of diesel generator sets, from an attached electric generator, which, when started, acts as a starter.

Contrary to popular belief, modern engines, traditionally called diesel engines, do not operate according to the Diesel cycle, but according to the Trinkler-Sabate cycle with a mixed heat supply.

The disadvantages of diesel engines are due to the peculiarities of the operating cycle - higher mechanical stress, requiring increased structural strength and, as a result, an increase in its dimensions, weight and increased cost due to a more complex design and the use of more expensive materials. Also, diesel engines, due to heterogeneous combustion, are characterized by inevitable soot emissions and an increased content of nitrogen oxides in the exhaust gases.

Gas engines

An engine that burns hydrocarbons as fuel, which are in a gaseous state under normal conditions:

• mixtures of liquefied gases - stored in a cylinder under saturated vapor pressure (up to 16 atm). The liquid phase or vapor phase of the mixture evaporated in the evaporator gradually loses pressure in the gas reducer to close to atmospheric pressure, and is sucked by the engine into the intake manifold through an air-gas mixer or injected into the intake manifold using electric injectors. Ignition is carried out using a spark that jumps between the electrodes of the spark plug.
• compressed natural gases - stored in a cylinder under a pressure of 150-200 atm. The design of power systems is similar to liquefied gas power systems, the difference is the absence of an evaporator.
• generator gas is a gas obtained by converting solid fuel into gaseous fuel. The solid fuel used is: coal
• peat
• wood

Rotary piston

Wankel engine cycle diagram: intake, compression, ignition, exhaust;
A - triangular rotor (piston), B - shaft. Additional information: Rotary-cylinder-valve engine

Proposed by the inventor Wankel at the beginning of the 20th century. The basis of the engine is a triangular rotor (piston), rotating in a special 8-shaped chamber, performing the functions of a piston, crankshaft and gas distributor. This design allows you to implement any 4-stroke cycle of a Diesel, Stirling or Otto without the use of a special gas distribution mechanism. In one revolution, the engine performs three complete power cycles, which is equivalent to the operation of a six-cylinder piston engine. Built serially by NSU in Germany (RO-80 car), VAZ in the USSR (VAZ-21018 Zhiguli, VAZ-416, VAZ-426, VAZ-526), ​​Mazda in Japan (Mazda RX-7, Mazda RX-8 ). Despite its fundamental simplicity, it has a number of significant design difficulties that make its widespread implementation very difficult. The main difficulties are associated with the creation of long-lasting, efficient seals between the rotor and the chamber and with the construction of a lubrication system.

In Germany at the end of the 70s of the 20th century there was a joke: “I will sell the NSU, I will give in addition two wheels, a headlight and 18 spare engines in good condition.”

• RCV is an internal combustion engine, the gas distribution system of which is implemented due to the movement of a piston, which performs reciprocating movements, alternately passing through the intake and exhaust pipes.

Combined internal combustion engine

• - an internal combustion engine, which is a combination of piston and blade machines (turbine, compressor), in which both machines participate to a comparable extent in the implementation of the work process. An example of a combined internal combustion engine is a piston engine with gas turbine supercharging (turbocharging). A great contribution to the theory of combined engines was made by the Soviet engineer, Professor A. N. Shelest.

Turbocharging

The most common type of combined engine is a piston with a turbocharger. A turbocharger or turbocharger (TC, TN) is a supercharger that is driven by exhaust gases. It got its name from the word “turbine” (French turbine from Latin turbo - vortex, rotation). This device consists of two parts: a turbine rotor wheel, driven by exhaust gases, and a centrifugal compressor, mounted on opposite ends of a common shaft. The jet of the working fluid (in this case, exhaust gases) acts on the blades fixed around the circumference of the rotor and sets them in motion together with the shaft, which is made integral with the turbine rotor from an alloy close to alloy steel. On the shaft, in addition to the turbine rotor, there is a compressor rotor made of aluminum alloys, which, when the shaft rotates, allows air to be pumped into the cylinders of the internal combustion engine. Thus, as a result of the action of exhaust gases on the turbine blades, the turbine rotor, shaft and compressor rotor simultaneously spin. The use of a turbocharger in conjunction with an air intercooler (intercooler) allows for the supply of denser air to the cylinders of the internal combustion engine (in modern turbocharged engines this is exactly the scheme used). Often, when a turbocharger is used in an engine, people talk about the turbine without mentioning the compressor. The turbocharger is one unit. It is impossible to use the energy of exhaust gases to supply an air mixture under pressure into the cylinders of an internal combustion engine using only a turbine. The injection is provided by the part of the turbocharger called the compressor.

At idle, at low speeds, the turbocharger produces little power and is driven by a small amount of exhaust gases. In this case, the turbocharger is ineffective, and the engine operates approximately the same as without supercharging. When a much higher power output is required from the engine, its speed, as well as the throttle clearance, increases. As long as there is enough exhaust gas to rotate the turbine, much more air is supplied through the intake manifold.

Turbocharging allows the engine to run more efficiently because the turbocharger uses energy from the exhaust gases that would otherwise be (mostly) wasted.

However, there is a technological limitation known as “turbojam” (“turbo lag”) (with the exception of engines with two turbochargers - small and large, when a small turbocharger operates at low speeds, and a large one at high speeds, jointly ensuring the supply of the required amount of air mixture to the cylinders or when using a variable geometry turbine, in motorsport forced acceleration of the turbine using an energy recovery system is also used [2]). The engine power does not increase instantly due to the fact that a certain time will be spent on changing the rotation speed of the engine, which has some inertia, and also due to the fact that the greater the mass of the turbine, the more time it will take to spin it up and create pressure, sufficient to increase engine power. In addition, increased exhaust pressure leads to the fact that the exhaust gases transfer part of their heat to the mechanical parts of the engine (this problem is partially solved by the manufacturers of Japanese and Korean internal combustion engines by installing an additional cooling system for the turbocharger with antifreeze).

Efficient specific fuel consumption

Mechanical efficiency of the engine

The effective power Ne developed by the engine is always less than its indicated power Ni, since part of the latter is spent on overcoming mechanical losses and driving the supercharger. The smaller the mechanical losses in the engine, the correspondingly larger part of the indicator power should be transferred to the engine shaft.

Mechanical efficiency of the engine

(ηM) is usually called the ratio of the effective engine power to the indicated one:

From this formula we can express the effective power in terms of indicator power and mechanical efficiency as follows: Ne = ηM Ni.

From the above formulas it is clear that mechanical efficiency is the proportion of the effective engine power from the indicator power. To find the effective power of the engine, you need to multiply its indicated power Ni by the mechanical efficiency ηM.

For engines without a supercharger, the mechanical efficiency is approximately 0.85÷0.90. This means that from 10 to 15 percent of its indicated power is spent on overcoming mechanical losses in the engine. For engines with superchargers mechanically driven from the crankshaft, a significant proportion of the indicated power is additionally spent on rotating the supercharger. As a result, the mechanical efficiency of such engines is correspondingly lower and averages about 0.70÷0.90.

For the ASh-62IR engine, which has a low-pressure supercharger, the mechanical efficiency value is 0.80÷0.90.

Efficient specific fuel consumption

(Ce) or, in short, effective fuel consumption is usually called fuel consumption per unit time (Ch) divided by a unit of effective power (Ne) developed by the engine.

If the engine develops effective power Ne and consumes fuel Ch per unit time, then its effective consumption is C e

will be:
Ce
=
Ch
·
N e
Effective specific consumption shows how much fuel per hour it is extremely important for the engine to consume to develop a unit of power (one horsepower). For the ASh-62IR engine, the effective fuel consumption depends on the operating mode and is equal to 200÷300 g/hp. h

.

The degree to which the heat introduced into the engine by the fuel is used to obtain efficient operation is characterized by effective efficiency.

Effective efficiency

(ηе) is usually called the ratio of the heat converted by the engine into effective work (Le) to the heat introduced by the fuel into the engine (Q).

However, effective efficiency takes into account all energy losses in the engine and characterizes it as a whole as a heat engine and as a system of mechanisms.

For modern aviation piston engines, the value of ηе is 0.2÷0.3. This means that only 20÷30% of the fuel consumed is used to create useful power, the remaining 70÷80% is irretrievably lost. For the ASh-62IR engine ηе≈0.20.

Operation cycles of piston internal combustion engines

Two-stroke cycle Diagram of a four-stroke engine, Otto cycle 1. intake 2. compression 3. stroke 4. exhaust
More information: Two-stroke engine and Four-stroke engine

Piston internal combustion engines are classified according to the number of strokes in the operating cycle into two-stroke and four-stroke.

The working cycle of four-stroke internal combustion engines takes two full revolutions of the crank or 720 degrees of crankshaft rotation (PCV), consisting of four separate strokes:

1. intake,
2. charge compression,
3. working stroke and
4. release (exhaust).

The change in operating strokes is ensured by a special gas distribution mechanism, most often it is represented by one or two camshafts, a system of pushers and valves that directly ensure a phase change. Some internal combustion engines used spool sleeves (Ricardo) for this purpose, having intake and/or exhaust ports. The communication of the cylinder cavity with the collectors in this case was ensured by the radial and rotational movements of the spool sleeve, which opened the desired channel with windows. Due to the peculiarities of gas dynamics - the inertia of gases, the time of occurrence of gas wind, the intake, power stroke and exhaust strokes in a real four-stroke cycle overlap, this is called valve timing overlap

. The higher the engine operating speed, the greater the phase overlap and the greater it is, the less torque of the internal combustion engine at low speeds. Therefore, in modern internal combustion engines, devices are increasingly being used that make it possible to change the valve timing during operation. Engines with electromagnetic valve control (BMW, Mazda) are especially suitable for this purpose. There are also engines with a variable compression ratio (SAAB AB), which have greater flexibility in performance.

Two-stroke engines have many layout options and a wide variety of design systems. The basic principle of any two-stroke engine is that the piston performs the functions of a gas distribution element. The work cycle consists, strictly speaking, of three strokes: the power stroke, which lasts from top dead center ( TDC

) to 20-30 degrees before bottom dead center (
BDC
), scavenging, which actually combines intake and exhaust, and compression, lasting from 20-30 degrees after BDC to TDC. Purging, from the point of view of gas dynamics, is the weak link of the two-stroke cycle. On the one hand, it is impossible to ensure complete separation of the fresh charge and exhaust gases, so either loss of the fresh mixture is inevitable, literally flying into the exhaust pipe (if the internal combustion engine is diesel, we are talking about air loss), on the other hand, the power stroke lasts not half revolution, but less, which in itself reduces efficiency. At the same time, the duration of the extremely important gas exchange process, which occupies half of the operating cycle in a four-stroke engine, cannot be increased. Two-stroke engines may not have a valve timing system at all. However, if we are not talking about simplified cheap engines, a two-stroke engine is more complex and expensive due to the mandatory use of a blower or a supercharging system; the increased thermal stress of the cylinder-piston engine requires more expensive materials for pistons, rings, and cylinder liners. The piston's performance of the functions of a gas distribution element requires its height to be no less than the piston stroke + the height of the purge windows, which is not critical in a moped, but significantly makes the piston heavier even at relatively low power. When power is measured in hundreds of horsepower, the increase in piston mass becomes a very serious factor. The introduction of vertical stroke distributor sleeves in Ricardo engines was an attempt to make it possible to reduce the size and weight of the piston. The system turned out to be complex and expensive to implement; except for aviation, such engines were not used anywhere else. Exhaust valves (with direct-flow valve purge) have twice the heat intensity compared to exhaust valves of four-stroke engines and worse conditions for heat removal, and their seats have longer direct contact with the exhaust gases.

The simplest in terms of operating procedures and the most complex in terms of design is the Koreyvo system, represented in the USSR and Russia, mainly by diesel locomotive diesel engines of the D100 series and tank diesel engines KhZTM. Such an engine is a symmetrical two-shaft system with diverging pistons, each of which is connected to its own crankshaft. Thus, this engine has two crankshafts, mechanically synchronized; the one connected to the exhaust pistons is 20-30 degrees ahead of the intake pistons. Due to this advance, the quality of the purge improves, which in this case is direct-flow, and the filling of the cylinder improves, since at the end of the purge the exhaust ports are already closed. In the 30s - 40s of the XX century, schemes with pairs of divergent pistons were proposed - diamond-shaped, triangular; There were aviation diesel engines with three star-shaped diverging pistons, of which two were intake and one was exhaust. In the 20s, Junkers proposed a single-shaft system with long connecting rods connected to the pins of the upper pistons by special rocker arms; the upper piston transmitted forces to the crankshaft through a pair of long connecting rods, and there were three shaft elbows per cylinder. There were also square pistons for purge cavities on the rocker arms. Two-stroke engines with divergent pistons of any system have mainly two disadvantages: firstly, they are very complex and large, and secondly, the exhaust pistons and liners in the area of ​​the exhaust ports have significant temperature stress and a tendency to overheat. Exhaust piston rings are also thermally stressed and are prone to coking and loss of elasticity. These features make the design of such engines a non-trivial task.

CV engines are equipped with a camshaft and exhaust valves. This significantly reduces the requirements for materials and design of the CPG. Intake is through windows in the cylinder liner, opened by the piston. This is exactly how most modern two-stroke diesel engines are configured. The window area and the liner in the lower part are in many cases cooled by charge air.

In cases where one of the main requirements for the engine is to reduce its cost, different types of crank-chamber contour window-window blowing are used - loop, return-loop (deflector) in various modifications. To improve engine parameters, various design techniques are used - variable length of the intake and exhaust channels, the number and location of bypass channels can be varied, spool valves, rotating gas shut-off valves, sleeves and curtains are used that change the height of the windows (and, accordingly, the moments at which the intake and exhaust begin) . Most of these engines are air-passively cooled. Their disadvantages are the relatively low quality of gas exchange and loss of the combustible mixture during purging; if there are several cylinders, sections of the crank chambers have to be separated and sealed; the crankshaft design becomes more complicated and more expensive.

Effective efficiency and specific effective fuel consumption

The economical operation of the engine as a whole is determined by the effective efficiency

ni and specific effective fuel consumption ge. Effective efficiency

evaluates the degree of use of fuel heat, taking into account all types of losses, both thermal and mechanical, and represents the ratio of heat Qe, equivalent to useful effective work, to all expended heat Gt*Q, i.e. nm=Qe/(Gt*(Q^p)n)=Ne/(Gt*(Q^p)n) (2).

Since the mechanical efficiency is equal to the ratio of Ne to Ni, then, substituting in

equation that determines the mechanical efficiency nm, the values ​​of Ne and Ni from

equations (1) and (2), we obtain nm=Ne/Ni=ne/ni, whence ne=ni/nM, i.e. The effective efficiency of the engine is equal to the product of the indicator efficiency and the mechanical efficiency.

Specific effective fuel consumption [kg/(kW*h)] is the ratio of second fuel consumption Gt to effective power Ne, i.e. ge=(Gt/Ne)*3600, or [g/(kW*h)] ge=(Gt/Ne)*3.6*10^6.

Engine thermal balance

From an analysis of the engine operating cycle, it follows that only part of the heat released during fuel combustion is used for useful work, while the rest constitutes heat losses. The distribution of heat obtained during the combustion of fuel introduced into the cylinder is called heat balance, which is usually determined experimentally. The heat balance equation has the form Q=Qe+Qg+Qn.s+Qrest, where Q is the heat of the fuel introduced into the engine; Qe is the heat converted into useful work; Qcool - heat lost by the cooling agent (water or air); Qg - heat lost with exhaust gases; Qн.с is the heat lost due to incomplete combustion of fuel, Qres is the residual member of the balance, which is equal to the sum of all unaccounted losses.

Amount of available (introduced) heat (kW) Q=Gt*(Q^p)n. Heat (kW) converted into useful work, Qe=Ne. Heat (kW) lost with cooling water, Qcool = Gw*sv*(t2-t1), where Gw is the amount of water passing through the system, kg/s; sv – heat capacity of water, kJ/(kg*K) [sv=4.19 kJ/(kg*K)]; t2 and t1 are the water temperatures at the entrance to the system and at the exit from it, C.

Thermal balance of the engine. Definition, components of the thermal balance, the influence of load, speed mode on the thermal balance of the engine.

The thermal balance of an engine is the distribution of heat from burnt fuel into its components: useful work, heat losses with exhaust gases, heat losses in the cooling system, mechanical losses, noise and vibration.

The influence of various factors on the thermal balance of the engine

The distribution of heat in the engine is influenced by factors such as crankshaft speed, load, mixture composition, and ignition timing.

Crankshaft rotation speed.

As the crankshaft rotation speed increases, the absolute values ​​of all components of the heat balance increase, since a greater amount of heat enters the engine per unit time.
Changes in the relative values ​​of the heat balance depending on the crankshaft speed. With increasing load, the value of qe increases to a maximum when the product ni*nm takes on the greatest value. A further decrease in de is associated with the enrichment of the mixture at full load, while the proportion qns increases. The influence of load on the components of the heat balance : a - change in absolute values; b -
change in relative values. The influence of the ignition timing on the components of the engine thermal balance.
Ignition timing.
The largest values
​​of q
correspond to the optimal value of the ignition angle (Fig. 6.6). Heat losses to the cooling system increase with both early and late ignition, since combustion in these cases occurs under unfavorable conditions. With late ignition, heat loss with the exhaust gases increases, since afterburning occurs already at the stage of the expansion process. The ignition timing does not affect losses associated with incomplete combustion, since the excess air coefficient remains unchanged.

5. Mixture formation in diesel engines. Features of mixture formation, types of combustion chambers. What is the essence of volume-film mixture formation. The mixture formation process is carried out as a result of fuel atomization using a high-pressure nozzle, directed vortex movement of the charge in the chamber, and sometimes also by regulating the temperature of the parts on which the fuel evaporates. Depending on the nature of fuel injection, there are volumetric, film and volumetric-film (mixed) types of mixture formation, which are carried out in undivided combustion chambers.

Volumetric mixing

— fuel injection is carried out into the air.
With this method, fuel is not allowed to enter the walls of the combustion chamber. Such mixture formation occurs in 2-stroke engines . Film mixture formation
- the main part of the fuel falls on the walls of the chamber and spreads in the form of a thin liquid film. In this case, for good ignition, about 5% of the fuel is injected into the compressed air, and the rest of it is injected onto the walls. part of the fuel is injected into the air, and part onto the walls.

One of the methods of volume-film mixture formation was proposed by Meurer and developed by MAN (Germany). It is characterized by the following features: - for better ignition and combustion, 5% of the fuel is injected into the compressed air, and the bulk of the fuel (95%) is applied to the walls in the form of a film 10-15 microns thick; - the fuel injected into the heated air self-ignites and then ignites the combustible mixture , formed in the process of evaporation of the film from the cylinder walls and mixing of fuel vapors with air; - fuel from the surface of the walls at the beginning of combustion evaporates relatively slowly and combustion begins slowly. Then the processes accelerate, while the piston goes to BDC and therefore the engine runs softly and silently; - this combustion process allows the use of various fuels in the engine: gasoline, kerosene, naphtha, diesel oil, etc. - the combustion chamber has developed displacers that create an intense vortex movement of an air charge, which promotes good evaporation and mixture formation. Engines with a similar process are called multi-fuel engines. Combustion chamber types: Divided

During the swirl chamber, as well as the pre-chamber combustion process, diesel fuel enters the preliminary chamber, where it is mixed with air and ignited.
If the chamber is shaped like a sphere, the air can swirl intensely, forming a vortex. And the prechamber design provides for the presence of thin channels, through which the mixture becomes more homogeneous. As you can see, in a divided chamber of any type, the fuel burns “in two steps.” This helps reduce the load on the piston group. The disadvantage is not the best starting qualities and an increase in fuel consumption, which arises due to the additional costs of pumping the mixture between the chambers. Undivided "
Diesel" with an undivided combustion chamber is always equipped with a direct injection system. Such engines, of course, are much more economical than engines of any other design. But the use of direct injection on diesel engines with high crankshaft speeds entails many different problems. The main ones are vibration and noise, which become most noticeable during overclocking.

6. Engine testing. Purpose and types of engine testing.

Research tests, Development tests, Reliability tests, Boundary tests, Control tests, Preliminary control tests, Interdepartmental tests, Serial tests, Acceptance tests Periodic tests, Type tests.

8. Kinematics of the crankshaft. What is the reason for the unevenness of the torque? What are the ways to reduce the unevenness of the torque? The crank mechanism (KSM) is the main mechanism of a piston internal combustion engine, which receives and transmits significant loads. Therefore, calculating the strength of KShM is important. In turn, calculations of many engine parts depend on the kinematics and dynamics of the crankshaft. Kinematic analysis of a crankshaft establishes the laws of motion of its parts, primarily the piston and connecting rod. The crank mechanism (crank mechanism) serves to convert the translational motion of the piston into the rotational movement of the crankshaft. When considering the kinematics of the crankshaft, it is assumed that the angular velocity of rotation of the crankshaft is constant. In fact, due to the unevenness of the engine torque, the angular velocity of the shaft is variable, but varies within insignificant limits. There are three main types of CV gears:

- central (normal) crankshaft, in which the cylinder axis intersects the crankshaft rotation axis

- offset (disaxial) crankshaft, in which the cylinder axis does not pass through the crankshaft axis, while the displacement of the cylinder axis “C”, which is called disaxial, usually does not exceed 10% of the piston stroke

- A crankshaft with a trailed connecting rod, in which two connecting rods transmit forces to the same crankpin (Fig. 7.1, c). The connecting rod connected to the neck is called the main connecting rod, the connecting rod pivotally connected to the lower head - the main connecting rod - is called the trailing rod. The piston articulated with the main connecting rod is called the main piston, and the piston articulated with the trailing connecting rod is called the side piston. In general, two trailing connecting rods (W-shaped engine) or more than two (star-shaped engine) can be connected to the main connecting rod.

9.The operational properties of a vehicle are the properties that characterize its performance of transport and special work: transportation of passengers, cargo and special equipment. These properties determine the vehicle’s suitability to operating conditions, as well as its efficiency and ease of use. A car has a number of operational properties (Fig. 1.1), which form two groups, related and not related to the movement of the car.

Traction, speed and braking properties, fuel efficiency, controllability, Turning, maneuverability, stability, maneuverability, smoothness, environmental friendliness and safety ensure the movement of cars and determine its patterns.

Capacity, strength, durability, adaptability to maintenance and repair, loading and unloading, boarding and disembarking passengers largely determine the efficiency and ease of use of a car.

What are the performance properties of a car? Let us define these properties.

traction-speed properties are the properties of a car that determine the range of changes in speeds and maximum acceleration accelerations in various road conditions when operating in traction mode.

Traction is the mode of movement of a car in which the power and torque necessary for movement are supplied from the engine to the drive wheels through the transmission.

Braking properties are those properties of a car that determine the maximum deceleration when braking in various road conditions and ensure that it remains stationary relative to the road surface.

Fuel efficiency is a property of a vehicle that determines fuel consumption during transportation work.

Controllability is the property of a car to change or maintain movement parameters when the driver influences the steering.

Additional units required for internal combustion engines

The disadvantage of the internal combustion engine is that it produces its highest power only in a narrow rpm range. Therefore, an integral attribute of an internal combustion engine is the transmission. Only in certain cases (for example, in airplanes) can one do without a complex transmission. The idea of ​​a hybrid car, in which the engine always operates in optimal mode, is gradually conquering the world.

In addition, an internal combustion engine requires a power system (for supplying fuel and air - preparing a fuel-air mixture), an exhaust system (for removing exhaust gases), and also cannot do without a lubrication system (designed to reduce friction forces in engine mechanisms and protect parts engine from corrosion, as well as together with the cooling system to maintain optimal thermal conditions), cooling systems (to maintain optimal thermal conditions of the engine), starting system (starting methods are used: electric starter, using an auxiliary starting engine, pneumatic, using human muscle power ), ignition system (to ignite the fuel-air mixture, used in engines with forced ignition).

Why is diesel efficiency higher?

Currently reading
Device, repair of muffler resonator

How often to change the timing belt on a car: what you need...

The efficiency indicator for different engines can vary greatly and depends on a number of factors. Gasoline engines have relatively low efficiency due to the large number of mechanical and thermal losses that occur during the operation of a power unit of this type.

The second factor is friction that occurs during the interaction of mating parts. Most of the useful energy consumption is driven by the movement of the engine pistons, as well as the rotation of parts inside the motor, which are structurally fixed to bearings. About 60% of the combustion energy of gasoline is spent only to ensure the operation of these units.

Additional losses are caused by the operation of other mechanisms, systems and attachments. The percentage of resistance losses at the moment of admission of the next charge of fuel and air, and then the release of exhaust gases from the internal combustion engine cylinder, is also taken into account.

If we compare a diesel unit and a gasoline engine, a diesel engine has a noticeably higher efficiency compared to a gasoline unit. Gasoline power units have an efficiency of about 25-30% of the total amount of energy received.

In other words, out of 10 liters of gasoline spent on engine operation, only 3 liters are used to perform useful work. The rest of the energy from fuel combustion was lost.

As for the efficiency of an atmospheric diesel unit, this figure is about 40%. Installing a turbocharger allows you to increase the mark to an impressive 50%. The use of modern fuel injection systems on diesel internal combustion engines in combination with a turbine made it possible to achieve an efficiency of about 55%.

This difference in the performance of structurally similar gasoline and diesel internal combustion engines is directly related to the type of fuel, the principle of formation of the working fuel-air mixture and the subsequent implementation of charge ignition. Gasoline units are more efficient than diesel units, but large losses are associated with the consumption of useful energy for heat. It turns out that the energy of gasoline is less efficiently converted into full-fledged mechanical work, and a large portion is simply dissipated by the cooling system into the atmosphere.

We also recommend reading the article on how to increase the power of a diesel engine using chip tuning. From this article you will learn about what engine ECU firmware is and what results are achieved by changing the standard parameters of the controller.

see also

• History of the creation of internal combustion engines
• Starting the internal combustion engine
• Internal combustion engine cooling system
• Philippe Le Bon was a French engineer who received a patent in 1801 for an internal combustion engine with compression of a mixture of gas and air.
• Rotary engine: designs and classification
• Rotary piston engine (Wankel engine)
• Turbo compound engine
• Car with gas generator
• Synthetic liquid fuel

The concept of “engine efficiency”

First, let's look at what efficiency is and how to consider this concept in the aspect of a car engine. Efficiency is represented by an indicator that displays the efficiency of a particular mechanism regarding the conversion of received energy into useful work. The indicator is displayed as a percentage.

In the case of an internal combustion engine, we are talking about the conversion of thermal energy, which is the product of fuel combustion in the engine cylinders. Efficiency in this case reflects the actually realized mechanical work, which directly depends on how much energy the piston receives from fuel combustion. This parameter is also affected by the final power that the installation delivers to the crankshaft.