Car Parts and Accessories

In a petrol engine a mixture of petrol and air enters the cylinders and is ignited by an electric spark from the spark-plug. In a diesel engine, only air enters the cylinder on the intake stroke.

Ignition in a diesel engine is caused by compression, which raises the temperature of air in the combustion chamber above the flash-point, or self-ignition temperature, of the fuel.

Diesel fuel, less easily evaporated than petrol, is not drawn in with air as a mixture, but is sprayed under high pressure from an injector into the combustion chamber, where it ignites on contact with the hot, compressed air. Each injector is supplied with fuel in metered quantities and at a high pressure by an engine-driven pump. The accelerator controls the amount of fuel delivered by the pump, and hence the power delivered by the engine. The diesel’s advantages lie in its greater efficiency (resulting in lower fuel costs), longer life and lower maintenance costs. Its disadvantages include a high initial cost, greater weight, a somewhat rougher idling, some smell, a higher noise level and slower acceleration.

In a medium-sized car, the air/fuel mixture is compressed to about one-ninth of its original volume, giving a compression ratio of 9:1; in a diesel engine the air may be compressed to as high as 22: 1, to increase the temperature of air to the flash-point temperature of the diesel fuel. A diesel engine has a much smaller combustion chamber and its higher compression ratio results in greater efficiency, because more potential heat-energy is converted into power.

To ensure that the correct amount of fuel is injected at the right moment, each cylinder on a diesel engine is fitted with an injector. A pump, driven at half crankshaft speed, forces fuel into the combustion cylinders in their firing order.

In the diesel 4-stroke cycle, pure air is drawn into the cylinder on the suction stroke; fuel is injected and starts to burn towards the end of the rising compression stroke; pressure from expanding gases forces the piston down on its power stroke; and burnt gases escape as the piston rises on its exhaust stroke.

In some diesel engines, a heater plug (glow plug) is fitted to help starting in low temperatures. This does not produce a spark but glows until air temperature in the cylinders is high enough to ensure self-ignition of the fuel sprayed into the combustion chamber during cranking.

Car Engine/the Rotary design

Rotary ‘Wankel’ engines — after their German inventor — were first produced in 1964, but early enthusiasm has waned following the unreliability of early models. Some manufacturers — notably the Japanese motor industry — have solved reliability problems, but only at a considerable cost, and the Rotary engine has become a rarity.

The great advantage of the rotary engine is that nothing goes up and down, only round and round. It is lighter, more compact and has fewer moving parts than a piston engine.

The Wankel has a fixed casing, with the internal shape of a wide-waisted figure of-eight, and a near-triangular rotor. For higher power the engine can have two or more rotors phased together. The output shaft turns at three times the rotor speed.

The rotor revolves eccentrically within the casing in such a way that the three rotor tips are continually in contact with the internal surface. Planetary gearing connects the rotor to an output shaft which is equivalent to the crankshaft of a piston engine.

Between the three sides of the rotor and the inside of the casing are three working spaces, or chambers, each of which alternately expands and contracts in size as the rotor ‘orbits’.

The casing is provided with one or two spark-plugs and an exhaust port. It may also incorporate an inlet port, although this is usually in the side housings. The ports are uncovered as the rotor revolves.

As a result, a 4-phase operating cycle occurs in each chamber during each orbit of the rotor, corresponding to the 4-stroke cycle of a piston engine — namely induction, compression, power and exhaust. As there are three chambers between the sides of the triangular rotor and the casing, it follows that there are three power ‘strokes‘ for each rotor revolution.

Sealing the gases

Efficient gas seals have to be provided at the three tips of the rotor and at the sides. The development of effective and durable seals has been a major problem.

Although most Wankel engines have a carburettor, some have been operated with fuel injection.

Possibly related posts: (automatically generated)
The Diesel Car Engine

• Off Road Four Car Driving: Cautious about Wading through the Water continued
• Engine Variations in Layout
• Auto Pistons and Connecting Rods of Car Engine
• PETROL OR DIESEL?
• Mechanics of the Car
• All thumbs up guide to car Glossary
• Checking the Car Basics, Before Hit on the Road
• How heat becomes driving power in Car Engine?
• Inlet Manifold and Automobile Carburettors
• Petrol injection, Auto Fuel System and Auto Part Repair Guide