6. Practical solutions of pneumatic piston engines

The pneumatic two-stroke piston engine is a simple solution of a real non-conventional driving system, which does not produce toxic gaseous components and does not burn any fuel. However, for filling the bottle with the air under high pressure, a mechanical energy is required for driving of a compressor. It is mostly a piston compressor allowing for obtaining high pressure driven by an electric motor, and energy is obtained from power station (combustion of coal, biomass, nuclear energy, gasification of coal).

## 6.1. Control valves of air inflow

The important element of every pneumatic engine is the pneumatic valve, which delivers the air in defined time to the cylinder. The air is injected by the valve to the cylinder, where the air charge is compressed due to the movement of the piston towards TDC. The greater outlet area of the injector is required for a large mass flow rate of air. For such case, the poppet valve in the injector sometimes is used. The proposal of the injector with poppet valve is shown in Figure 10, where the movement of the valve is controlled by a cam mechanism. Because of high pressure from the inlet side, the moving part of the valve has two parts: poppet and cylindrical parts with the same diameter. This arrangement allows for maintenance of the valve in the closed condition without additional force and closing of the poppet valve required a small force of the return spring. The piston of the valve has a labyrinth sealing and also sealing between the valve stem and the body. The whole controlled mechanism is like as in the timing mechanism in the four-stroke engine. The cam system gives a constant angle of opening of the valve (in CA deg) in relation to crankshaft rotation. Better solution of controlled motion of poppet valve in the air injector is applying of an electronic unit by using an induction coil where electromagnetic forces enable the movement of valve stem. The simpler but practical solution of the air injector controlled by solenoid unit is shown in Figure 11a. The valve stem should have a limiter of movement. Electromagnetic force for opening of valve lasts very short and is independent of the movement and position of the crankshaft. The poppet valve can be opened and closed at any time. Another proposed solution is utilization of the standard

sprayer of diesel oil with higher nozzle diameter and by cutting of the dispenser cap, but with

Figure 11. Electromagnetic valves: (a) air poppet valve controlled by ECU and electric coil and (b) utilizing of standard

Modern Pneumatic and Combustion Hybrid Engines http://dx.doi.org/10.5772/intechopen.69689 143

Such design of an injector tip revamped is presented in Figure 11b and it was applied by Wiatrak [30] in his pneumatic engine in moped. This configuration of the air injector does not require any modification of ECU and allows control of air injection in any way. Limitation of

Some solutions of pneumatic engines can be found in the literature and widely in Internet. One of the promising solutions was given by Kumar et al. [28]. They tested a two-stroke engine equipped with storage cylinder, pressure regulator, air filter and lubricator, modified flywheel

contact of the needle spray with the body (Figure 11b).

Figure 10. Proposal of air dosing valve driven by a cam mechanism.

6.2. Two-stroke Indian pneumatic engine

sprayer of CI engine.

applying such injector tip is only the required air mass flow rate.

Figure 10. Proposal of air dosing valve driven by a cam mechanism.

4. The increase of the engine torque can be assured by the increase of the air injection

5. Low temperature at the end of expansion process should not cause a lubrication problem, because the mean temperature of the charge is near the ambient temperature. The wall temperature in every two-stroke engine is stable for steady load. In such case, the engine does not require any cooling system. Lubrication in such engine should be carried out by dosing of lubrication oil to the inlet pipe by a special needle valve with possible regulation

The design of the pneumatic engine is based on the classic two-stroke engine and it needs small changes in order to mount the air feeding system with electronic control unit (ECU)

The pneumatic two-stroke piston engine is a simple solution of a real non-conventional driving system, which does not produce toxic gaseous components and does not burn any fuel. However, for filling the bottle with the air under high pressure, a mechanical energy is required for driving of a compressor. It is mostly a piston compressor allowing for obtaining high pressure driven by an electric motor, and energy is obtained from power station (com-

The important element of every pneumatic engine is the pneumatic valve, which delivers the air in defined time to the cylinder. The air is injected by the valve to the cylinder, where the air charge is compressed due to the movement of the piston towards TDC. The greater outlet area of the injector is required for a large mass flow rate of air. For such case, the poppet valve in the injector sometimes is used. The proposal of the injector with poppet valve is shown in Figure 10, where the movement of the valve is controlled by a cam mechanism. Because of high pressure from the inlet side, the moving part of the valve has two parts: poppet and cylindrical parts with the same diameter. This arrangement allows for maintenance of the valve in the closed condition without additional force and closing of the poppet valve required a small force of the return spring. The piston of the valve has a labyrinth sealing and also sealing between the valve stem and the body. The whole controlled mechanism is like as in the timing mechanism in the four-stroke engine. The cam system gives a constant angle of opening of the valve (in CA deg) in relation to crankshaft rotation. Better solution of controlled motion of poppet valve in the air injector is applying of an electronic unit by using an induction coil where electromagnetic forces enable the movement of valve stem. The simpler but practical solution of the air injector controlled by solenoid unit is shown in Figure 11a. The valve stem should have a limiter of movement. Electromagnetic force for opening of valve lasts very short and is independent of the movement and position of the crankshaft. The poppet valve can be opened and closed at any time. Another proposed solution is utilization of the standard

pressure but it causes higher specific air consumption.

6. Practical solutions of pneumatic piston engines

bustion of coal, biomass, nuclear energy, gasification of coal).

of mass flow rate.

142 Improvement Trends for Internal Combustion Engines

6.1. Control valves of air inflow

system.

Figure 11. Electromagnetic valves: (a) air poppet valve controlled by ECU and electric coil and (b) utilizing of standard sprayer of CI engine.

sprayer of diesel oil with higher nozzle diameter and by cutting of the dispenser cap, but with contact of the needle spray with the body (Figure 11b).

Such design of an injector tip revamped is presented in Figure 11b and it was applied by Wiatrak [30] in his pneumatic engine in moped. This configuration of the air injector does not require any modification of ECU and allows control of air injection in any way. Limitation of applying such injector tip is only the required air mass flow rate.

#### 6.2. Two-stroke Indian pneumatic engine

Some solutions of pneumatic engines can be found in the literature and widely in Internet. One of the promising solutions was given by Kumar et al. [28]. They tested a two-stroke engine equipped with storage cylinder, pressure regulator, air filter and lubricator, modified flywheel

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; 12, magnetic sensor [28].

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.

Chinese researchers conducted numerous analyses of a small engine to find an optimal work efficiency, high torque and an optimal control parameters of injection of the air. Figure 14a presents an ideal power and engine efficiency as a function of pressure of the injected air. The engine power decreases with increasing of the air pressure, but engine efficiency linearly increases. It should pay attention to high efficiency above 56% at a pressure inlet of 1.5 MPa. Engine efficiency depends mainly on timing of the injection valve. Figure 14b presents the total efficiency of air powered engines (APE) for different duration of the air injection from 10 to 50 CA at a starting point of injection 5 CA BTDC. Engine efficiency slightly decreases with increasing of rotational speed and for longer opening of the air injector, the engine efficiency

Figure 14. Engine performance: (a) ideal power and working efficiency at different air inlet pressure and (b) working

Modern Pneumatic and Combustion Hybrid Engines http://dx.doi.org/10.5772/intechopen.69689 145

The Chinese researcher found that 'the virtual prototype of the APE can make the simulation more precise and reduce the cost of the design. This research can provide theoretical supports

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

decreases from 54 to 42% at an engine rotational speed of 800 rpm.

7.1. Conception of vehicle with pneumatic and combustion engine

to the new APE prototype's design and optimization' [16].

efficiency of APE at different rotational speeds [29].

7. Pneumatic and combustion hybrid engine

#### 6.3. Small power air engine

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].

Figure 14. Engine performance: (a) ideal power and working efficiency at different air inlet pressure and (b) working efficiency of APE at different rotational speeds [29].

Chinese researchers conducted numerous analyses of a small engine to find an optimal work efficiency, high torque and an optimal control parameters of injection of the air. Figure 14a presents an ideal power and engine efficiency as a function of pressure of the injected air. The engine power decreases with increasing of the air pressure, but engine efficiency linearly increases. It should pay attention to high efficiency above 56% at a pressure inlet of 1.5 MPa.

Engine efficiency depends mainly on timing of the injection valve. Figure 14b presents the total efficiency of air powered engines (APE) for different duration of the air injection from 10 to 50 CA at a starting point of injection 5 CA BTDC. Engine efficiency slightly decreases with increasing of rotational speed and for longer opening of the air injector, the engine efficiency decreases from 54 to 42% at an engine rotational speed of 800 rpm.

The Chinese researcher found that 'the virtual prototype of the APE can make the simulation more precise and reduce the cost of the design. This research can provide theoretical supports to the new APE prototype's design and optimization' [16].
