7. Pneumatic and combustion hybrid engine

and solenoid valve working with 24 V DC with a maximum pressure of 10 bar. A schematic diagram of compressed air engine worked out by Indian scientists is shown in Figure 12.

Figure 12. Scheme of compressed air engine: 1, storage cylinder; 2, stop valve; 3, pressure regulator; 4, hose; 5, solenoid valve; 6, air filter and lubricator; 7, adapter nipple; 8, two-stroke SI engine; 9, flywheel; 10, gearbox; 11, transmission shaft;

Another solution was presented by Chinese scientists, represented by Xu et al. [29], in their work concerning an adaptation of four-stroke engine working on compressed air. They have developed a mathematical model of filling the cylinder and control model of the engine. The virtual model of the pneumatic engine is shown in Figure 13. Their work concerns mainly to theoretical analysis of working performance also in dynamic loads by using SIMULINK. The

Figure 13. Physical model of APE: 1, balanced valves; 2, cylinder cover; 3, cylinder; 4, crankshaft; 5, crank piston

mechanism; 6, timing gears; 7, camshaft; 8, cam follower; 9, tunable rocker mechanism [29].

6.3. Small power air engine

144 Improvement Trends for Internal Combustion Engines

12, magnetic sensor [28].

#### 7.1. Conception of vehicle with pneumatic and combustion engine

The proposal concerns to a certain hybrid combustion system in internal combustion engines both compression and spark ignition (SI) in order to achieve higher indicated mean pressure and lower fuel consumption. The solution is combination of two fuelling systems: the first direct fuel injection and the second high pressure air injection. The dosing of both fluids is shifted in CA one relative to second. The additional air helps in the charge mixing, increasing of charge turbulence and causes a quicker combustion process by additional oxygen in the regions, where local excess air coefficient is small (below ignition boundary). Besides the fuel dose, the additional air increases the mass of charge in the cylinder causing a significant increment of pressure. This elaboration concerns only to applying of an air injection in compression ignition (CI) engines. The influence of an additional air dose on compression ignition engines can help to break the fuel jet with possibility to burn the droplets in the kernel of fuel jet. In this way, CI engine can reduce the amount of emitted soot and nanoparticles. The presented solution of combustion and pneumatic engine is based on the patent applications made by the Wiatrak and Mitianiec [30, 31]. The simple diagram of the solution is presented in Figure 15 for CI engine, but the same solution can be applied for SI engine and in this case instead of the diesel oil injector a spark plug will be located.

The electrical signal from ECU controls both the air pressure and time of opening and closing of the pneumatic valve. The electronic control of fuel injector and air injector enables to obtain optimal engine parameters by a small amount of fuel and air. The car with combustion and pneumatic engine can be driven by the piston engine working in four modes as follows: 1. Pneumatic mode (air injection at high pressure to the cylinder) without combustion.

Modern Pneumatic and Combustion Hybrid Engines http://dx.doi.org/10.5772/intechopen.69689 147

3. Combustion and full pneumatic mode for temporary high power during acceleration,

The combustion and pneumatic engine depending on working modes enables the following

• Driving of the vehicle with real-zero emission as a result of lower temperature (decreasing of NOx emission) and full fuel combustion by adding more air, which enables CO absence.

• Decreasing of soot emission in diesel engines as a result of higher concentration of oxygen

The driving resistance power depends on rolling forces and air resistance forces. The resistance force was measured by the Netherlands automotive research institution (TNO) [32] for car

where v is velocity of car on flat road in km/h. The car with mass 1250 kg driving with velocity 50 km/h on the flat road requires only 2.83 kW of power. Maximum power of engine which was tested according to New European Driving Cycle (NEDC) (t = 400 s) amounts 19 kW and engine work during the NEDC test reaches value 0.314 kWh. Another formula for calculation of driving forces of passenger cars in NEDC was given by the Austrian automotive research

For simulation of combustion and air injection process in internal combustion engine (ICE), a diesel engine being in production was chosen and some results of simulations are presented

company founded by Helmut List (AVL), on the basis of their measurements:

where α is an angle of inclination of the road and v is velocity of the car in km/h.

<sup>F</sup> <sup>¼</sup> <sup>114</sup>:<sup>22</sup> <sup>þ</sup> <sup>0</sup>:<sup>3861</sup> � <sup>ν</sup> <sup>þ</sup> <sup>0</sup>:<sup>0281</sup> � <sup>ν</sup><sup>2</sup> <sup>½</sup>N� (13)

<sup>F</sup> <sup>¼</sup> <sup>102</sup> <sup>þ</sup> <sup>6376</sup>:<sup>5</sup> � sin <sup>α</sup> <sup>þ</sup> <sup>0</sup>:<sup>02592</sup> � <sup>ν</sup><sup>2</sup> <sup>½</sup>N� (14)

4. Combustion with micro-dose of injected air for small increase of car load.

in the core of fuel jets (by optimal direction of injected air). • Decreasing of cooling heat from engine to the cooling system.

with mass 1700 kg and the following formula was given:

2. Combustion (CI or SI) engine (standard mode).

climbing and high velocity.

• Increasing of engine torque (power).

7.2. Pneumatic CI engine

• Decreasing of specific fuel consumption.

factors:

A high-pressure bottle contains the air under pressure below 500 bar, and the air is supplied to the pneumatic injector through the safe valve, pressure controller, which reduces high pressure according to the engine load. The electrical signal from ECU controls both the air pressure and time of opening and closing of the pneumatic valve.

Figure 15. Diagram of combustion and pneumatic CI engine [31].

The electrical signal from ECU controls both the air pressure and time of opening and closing of the pneumatic valve. The electronic control of fuel injector and air injector enables to obtain optimal engine parameters by a small amount of fuel and air. The car with combustion and pneumatic engine can be driven by the piston engine working in four modes as follows:


The combustion and pneumatic engine depending on working modes enables the following factors:

• Increasing of engine torque (power).

increment of pressure. This elaboration concerns only to applying of an air injection in compression ignition (CI) engines. The influence of an additional air dose on compression ignition engines can help to break the fuel jet with possibility to burn the droplets in the kernel of fuel jet. In this way, CI engine can reduce the amount of emitted soot and nanoparticles. The presented solution of combustion and pneumatic engine is based on the patent applications made by the Wiatrak and Mitianiec [30, 31]. The simple diagram of the solution is presented in Figure 15 for CI engine, but the same solution can be applied for SI engine and in this case

A high-pressure bottle contains the air under pressure below 500 bar, and the air is supplied to the pneumatic injector through the safe valve, pressure controller, which reduces high pressure according to the engine load. The electrical signal from ECU controls both the air pressure and

instead of the diesel oil injector a spark plug will be located.

time of opening and closing of the pneumatic valve.

146 Improvement Trends for Internal Combustion Engines

Figure 15. Diagram of combustion and pneumatic CI engine [31].


The driving resistance power depends on rolling forces and air resistance forces. The resistance force was measured by the Netherlands automotive research institution (TNO) [32] for car with mass 1700 kg and the following formula was given:

$$F = 114.22 + 0.3861 \cdot \nu + 0.0281 \cdot \nu^2 \text{ [N]} \tag{13}$$

where v is velocity of car on flat road in km/h. The car with mass 1250 kg driving with velocity 50 km/h on the flat road requires only 2.83 kW of power. Maximum power of engine which was tested according to New European Driving Cycle (NEDC) (t = 400 s) amounts 19 kW and engine work during the NEDC test reaches value 0.314 kWh. Another formula for calculation of driving forces of passenger cars in NEDC was given by the Austrian automotive research company founded by Helmut List (AVL), on the basis of their measurements:

$$F = 102 + 6376.5 \cdot \sin a + 0.02592 \cdot \nu^2 \text{ [N]} \tag{14}$$

where α is an angle of inclination of the road and v is velocity of the car in km/h.

#### 7.2. Pneumatic CI engine

For simulation of combustion and air injection process in internal combustion engine (ICE), a diesel engine being in production was chosen and some results of simulations are presented below. Simulation was carried out only on one-cylinder compression ignition (CI) four-stroke engine with a capacity of 450 cc. The results of calculations were obtained from the computer program by using 0-D thermodynamic model of engine work cycle with unsteady gas flow in engine pipes.

#### Technical data of engine:

Bore/stroke = 82/85 mm Length of connected rod = 130 mm Compression ratio = 16 Number of valves = 4 Inlet valve timing = 20 BTDC/35 ABDC Exhaust valve timing = 56 BBDC/20 ATDC Parameters of air injection:

Pressure = 350 bar

Timing of injector = TDC/35 ATDC

Flow area of valve exit = 5 mm<sup>2</sup> .

The diagram shown in Figure 16 presents variation of mean effective pressure and specific air consumption, which was fuelled only by the air at high injection pressure. Variation of these parameters is the same as for the two-stroke pneumatic engine. When the engine is supplied only with air, bmep rapidly decreases with growing rotational speed (lower value of torque).

At higher rotational speeds, the pneumatic engine has lower efficiency at the same air injection parameters. With increasing of engine rotational speed, the cylinder pressure decreases, because the time of air injection is shorter for the same duration of crank angle of the air valve

Figure 17. Cylinder pressure traces in one-cylinder CI four-stroke engine fuelled only by air injection at pressure 350 bar

Modern Pneumatic and Combustion Hybrid Engines http://dx.doi.org/10.5772/intechopen.69689 149

Figure 17 shows traces of pressure in one cylinder for considered CI pneumatic engine at different rotational speeds. The higher maximum pressure in the diesel engine supplied only with air takes place at lower rotational speeds. With the increase of engine speed, the maximum of air pressure in the cylinder still decreases. Calculations were carried out for CI engine at start of air injection at TDC, duration of injection 40 CA and air injection pressure 350 bar. The diesel pneumatic engine indicates higher specific air consumption at higher rotational speed, where the engine power has lower value. These parameters show that the pneumatic diesel engine indicates better working parameters at lower rota-

Simulation of CI engine with the same geometrical parameters as in the first option with additional air injection (350 bar) was carried out for different rotational speed. Variation of cylinder pressure is shown in Figure 18 for the CI engine fuelled only by diesel oil and for CI engine (the same air excess ratio λ = 1.5) with additional air injection. It is seen higher pressure in the cylinder during expansion stroke for the combustion and pneumatic mode than for CI engines only. Start of air injection was constant for all presented rotational speeds: opening 25

Figure 19 presents the variation of engine torque for both cases as a function of rotational speed. The big difference of engine torque and also engine power is observed particularly at

7.3. Combustion engine with additional dose of injected air

opening.

for different rotational speeds.

tional speeds.

CA ATDC and duration 40 CA.

The air mass consumption per one cycle decreases with rotational speed at the same air injection parameters, however, the specific air consumption increases with rotational speed.

Figure 16. Mean effective pressure and specific air consumption of one-cylinder CI four-stroke engine fuelled only by air injection at injection pressure 350 bar.

Figure 17. Cylinder pressure traces in one-cylinder CI four-stroke engine fuelled only by air injection at pressure 350 bar for different rotational speeds.

At higher rotational speeds, the pneumatic engine has lower efficiency at the same air injection parameters. With increasing of engine rotational speed, the cylinder pressure decreases, because the time of air injection is shorter for the same duration of crank angle of the air valve opening.

Figure 17 shows traces of pressure in one cylinder for considered CI pneumatic engine at different rotational speeds. The higher maximum pressure in the diesel engine supplied only with air takes place at lower rotational speeds. With the increase of engine speed, the maximum of air pressure in the cylinder still decreases. Calculations were carried out for CI engine at start of air injection at TDC, duration of injection 40 CA and air injection pressure 350 bar. The diesel pneumatic engine indicates higher specific air consumption at higher rotational speed, where the engine power has lower value. These parameters show that the pneumatic diesel engine indicates better working parameters at lower rotational speeds.

#### 7.3. Combustion engine with additional dose of injected air

below. Simulation was carried out only on one-cylinder compression ignition (CI) four-stroke engine with a capacity of 450 cc. The results of calculations were obtained from the computer program by using 0-D thermodynamic model of engine work cycle with unsteady gas flow in

engine pipes.

Technical data of engine:

Bore/stroke = 82/85 mm

148 Improvement Trends for Internal Combustion Engines

Compression ratio = 16 Number of valves = 4

Parameters of air injection:

Pressure = 350 bar

injection at injection pressure 350 bar.

Length of connected rod = 130 mm

Inlet valve timing = 20 BTDC/35 ABDC

Timing of injector = TDC/35 ATDC

Flow area of valve exit = 5 mm<sup>2</sup>

Exhaust valve timing = 56 BBDC/20 ATDC

.

The diagram shown in Figure 16 presents variation of mean effective pressure and specific air consumption, which was fuelled only by the air at high injection pressure. Variation of these parameters is the same as for the two-stroke pneumatic engine. When the engine is supplied only with air, bmep rapidly decreases with growing rotational speed (lower value of torque). The air mass consumption per one cycle decreases with rotational speed at the same air injection parameters, however, the specific air consumption increases with rotational speed.

Figure 16. Mean effective pressure and specific air consumption of one-cylinder CI four-stroke engine fuelled only by air

Simulation of CI engine with the same geometrical parameters as in the first option with additional air injection (350 bar) was carried out for different rotational speed. Variation of cylinder pressure is shown in Figure 18 for the CI engine fuelled only by diesel oil and for CI engine (the same air excess ratio λ = 1.5) with additional air injection. It is seen higher pressure in the cylinder during expansion stroke for the combustion and pneumatic mode than for CI engines only. Start of air injection was constant for all presented rotational speeds: opening 25 CA ATDC and duration 40 CA.

Figure 19 presents the variation of engine torque for both cases as a function of rotational speed. The big difference of engine torque and also engine power is observed particularly at

Figure 18. Comparison of cylinder pressure in the four-stroke CI engine and CI engine with additional air injection at 2000 rpm.

mode of engine work is needed for higher acceleration and load of the car and enables the retrieving of very high power density with dose of the air for only short time of operation. At

Figure 20. Comparison of specific fuel consumption in the four-stroke CI engine and CI engine with additional air

Modern Pneumatic and Combustion Hybrid Engines http://dx.doi.org/10.5772/intechopen.69689 151

This mode of engine work is needed for higher acceleration and load of the car and enables the retrieving of very high power density with dose of the air for only short time of operation. At

One of the possibilities of the combustion and pneumatic engine is working with a micro-dose of the pressurized air during normal compression ignition engine operation (combustion mode). The micro-dose of air is required, for example, by reducing CO emission or reducing combustion temperature, which influences on decreasing of NOx emission. However, this small dose of air increases significantly the engine power. This mode can be fulfilled by changing of duration of air injection. Figure 21 shows the variation of engine effective power with micro-dose of the air in comparison to the standard engine as a function of duration of the air valve opening. The specific fuel consumption for such working mode is considerably reduced (Figure 22). The presented results were calculated for 2500 rpm and at an air pressure of 350 bar. The value of brake specific fuel consumption (bsfc) decreases rapidly as a result of a

Change of pressure trace in the cylinder in the combustion and pneumatic engine depends on timing of the air valve. Variation of cylinder pressure is shown in Figure 23 for the same pressure of injected air (150 bar) but at different valve opening and at the same duration of

higher rotational speeds, only small dose of the air is required.

higher rotational speeds, only small dose of the air is required.

longer opening of air valve and delivering more air to the cylinder.

7.4. ICE with micro-dose of air

injection at different rotational speeds.

7.5. Strategy of control of air injection

Figure 19. Comparison of engine torque in the four-stroke CI engine and CI engine with additional air injection at different rotational speeds.

lower rotational speed, because in the pneumatic engine at the same duration of opening, the air injector more air is delivered to the cylinder in lower rotational speed because of longer time of opening of the air injector.

By adding the pressured air into small volume of the combustion chamber (almost at TDC), the engine power rapidly grows and for that reason the specific fuel consumption (diesel oil) decreases considerably, as shown in Figure 20 for engine with additional dose of the air. This

Figure 20. Comparison of specific fuel consumption in the four-stroke CI engine and CI engine with additional air injection at different rotational speeds.

mode of engine work is needed for higher acceleration and load of the car and enables the retrieving of very high power density with dose of the air for only short time of operation. At higher rotational speeds, only small dose of the air is required.

This mode of engine work is needed for higher acceleration and load of the car and enables the retrieving of very high power density with dose of the air for only short time of operation. At higher rotational speeds, only small dose of the air is required.

#### 7.4. ICE with micro-dose of air

One of the possibilities of the combustion and pneumatic engine is working with a micro-dose of the pressurized air during normal compression ignition engine operation (combustion mode). The micro-dose of air is required, for example, by reducing CO emission or reducing combustion temperature, which influences on decreasing of NOx emission. However, this small dose of air increases significantly the engine power. This mode can be fulfilled by changing of duration of air injection. Figure 21 shows the variation of engine effective power with micro-dose of the air in comparison to the standard engine as a function of duration of the air valve opening. The specific fuel consumption for such working mode is considerably reduced (Figure 22). The presented results were calculated for 2500 rpm and at an air pressure of 350 bar. The value of brake specific fuel consumption (bsfc) decreases rapidly as a result of a longer opening of air valve and delivering more air to the cylinder.

## 7.5. Strategy of control of air injection

lower rotational speed, because in the pneumatic engine at the same duration of opening, the air injector more air is delivered to the cylinder in lower rotational speed because of longer

Figure 19. Comparison of engine torque in the four-stroke CI engine and CI engine with additional air injection at

Figure 18. Comparison of cylinder pressure in the four-stroke CI engine and CI engine with additional air injection at

By adding the pressured air into small volume of the combustion chamber (almost at TDC), the engine power rapidly grows and for that reason the specific fuel consumption (diesel oil) decreases considerably, as shown in Figure 20 for engine with additional dose of the air. This

time of opening of the air injector.

different rotational speeds.

2000 rpm.

150 Improvement Trends for Internal Combustion Engines

Change of pressure trace in the cylinder in the combustion and pneumatic engine depends on timing of the air valve. Variation of cylinder pressure is shown in Figure 23 for the same pressure of injected air (150 bar) but at different valve opening and at the same duration of

Figure 21. Influence of duration of air injection on engine effective power at 2500 rpm.

Figure 22. Influence of duration of air injection on specific fuel consumption at 2500 rpm.

valve opening. By earlier opening of the air valve, one obtains a higher mean indicated pressure. The control of engine work can be realized by changing of timing of air injector opening for constant pressure. At high inlet air pressure, the flow is critical (sonic) and air velocity is constant and equalled to the local sound speed. The mass dose of the air can be controlled also by changing of the pressure, however, such regulation is not suitable for this application. The air is stored in the pressurized tank or bottles, which can be located in different places in the car. Simulation carried out in GT-Power program indicates lower emission of carbon monoxide in SI engine with air-added injection than in standard SI engine, because of higher concentration of oxygen in the combustion chamber (Figure 24).

The pneumatic system also enables the reducing of soot emission in diesel engines by earlier air injection in the region of the fuel jet core, where the amount of oxygen is not enough for complete burning and thus the soot is formed. Simulation of work performance was also carried out for SI engine with a compression ratio ε = 10 for the same geometrical data as for the compression ignition combustion and pneumatic engine. The obtained results have the same tendency of increasing power and decreasing of specific fuel consumption. The main task of the proposed system is applying of vehicles without exhaust pollution in the cities ('zero

Figure 24. Comparison of cylinder CO mass concentration at 3500 rpm for standard four-stroke CI and hybrid engine at

Figure 23. Pressure variation in a cylinder for different angles of air injection start at 3000 rpm in the four-stroke CI engine

Modern Pneumatic and Combustion Hybrid Engines http://dx.doi.org/10.5772/intechopen.69689 153

(combustion + air injection).

full load.

emission') and enabling a higher engine performance at different load of the car.

Figure 23. Pressure variation in a cylinder for different angles of air injection start at 3000 rpm in the four-stroke CI engine (combustion + air injection).

Figure 24. Comparison of cylinder CO mass concentration at 3500 rpm for standard four-stroke CI and hybrid engine at full load.

valve opening. By earlier opening of the air valve, one obtains a higher mean indicated pressure. The control of engine work can be realized by changing of timing of air injector opening for constant pressure. At high inlet air pressure, the flow is critical (sonic) and air velocity is constant and equalled to the local sound speed. The mass dose of the air can be controlled also by changing of the pressure, however, such regulation is not suitable for this application. The air is stored in the pressurized tank or bottles, which can be located in different places in the car. Simulation carried out in GT-Power program indicates lower emission of carbon monoxide in SI engine with air-added injection than in standard SI engine,

because of higher concentration of oxygen in the combustion chamber (Figure 24).

Figure 21. Influence of duration of air injection on engine effective power at 2500 rpm.

152 Improvement Trends for Internal Combustion Engines

Figure 22. Influence of duration of air injection on specific fuel consumption at 2500 rpm.

The pneumatic system also enables the reducing of soot emission in diesel engines by earlier air injection in the region of the fuel jet core, where the amount of oxygen is not enough for complete burning and thus the soot is formed. Simulation of work performance was also carried out for SI engine with a compression ratio ε = 10 for the same geometrical data as for the compression ignition combustion and pneumatic engine. The obtained results have the same tendency of increasing power and decreasing of specific fuel consumption. The main task of the proposed system is applying of vehicles without exhaust pollution in the cities ('zero emission') and enabling a higher engine performance at different load of the car.
