Brief idea on petrol engine.

PETROL ENGINES

                A petrol engine (known as a gasoline engine in American English) is an internal combustion engine with spark-ignition, designed to run on petrol (gasoline) and similar volatile fuels. It was invented in 1876 in Germany by German inventor Nikolaus August Otto. The first petrol combustion engine (one cylinder, 121.6 cm³ displacement) was prototype in 1882 in Italy by Enrico Bernardi. In most petrol engines, the fuel and air are usually pre-mixed before compression (although some modern petrol engines now use cylinder-direct petrol injection). The pre-mixing was formerly done in a carburetor, but now it is done by electronically controlled fuel injection, except in small engines where the cost/complication of electronics does not justify the added engine efficiency. The process differs from a diesel engine in the method of mixing the fuel and air, and in using spark plugs to initiate the combustion process. In a diesel engine, only air is compressed (and therefore heated), and the fuel is injected into very hot air at the end of the compression stroke, and self-ignites.

WORKING

i. Suction of air (is also known as breathing or aspiration).

ii. Mixing of the fuel with air after breaking the liquid fuel into highly atomised / mist form.

iii. Igniting the air-fuel mixture with an electric spark using spark plug.

iv. Burning of highly atomised fuel particles; which results in releasing / ejection of heat energy.

TYPES OF FUEL INJECTION SYSTEM IN PETROL ENGINES

Continuous type:-

In this type petrol is injected in to the inlet manifold continuously when the engine is running.

Intermittent type:-

In this type petrol is injected during the suction stroke only it is also known as timed or jerk type.

Direct type:-

In this type petrol is feed directly in to the glider.

Indirect type:-

In this type petrol is injected in to the inlet port or in to the inlet manifold.

Single point:-

In this type the petrol is injected through single injector.

Multi point :-

In this type petrol is injected by number of injector it is more advance and recent development it is computer control system it is having high fuel efficiency.

Electronic petrol injection system(commonly known as fuel injection):-

- In this system electronically controlled metering valve is used.

- The metering valve meters the desired quantity of petrol and supplied to injector.

- The opening injector is also controlled by electronically controlled so that electronic unit known as ECU which consider computer and sensor.

- The sensors sense the various engine conditions [tempter load speed air pressure] and sends the singles to the computer [E.C.U/E.C.M] the computer reads the singles to the sensor to operate the pump and nozzle.

Some disadvantage of using carburetor:

i.  With single carburetor it is difficult to supply to mixture uniformly to all cylinder.

ii. Ventura throat of carburetor restricts the smooth flow of mixture.

iii. Chock restricts the flow of mixture.

To solve the above said problem, electronic injection is necessary.

WORKING CYCLES

Petrol engines may run on the four-stroke cycle or the two-stroke cycle. For details of working cycles see:

·         Four-stroke cycle

·         Two-stroke cycle

·         Wankel engine

CYLINDER CONFIGURATION

Common cylinder arrangements are from 1 to 6 cylinders in-line or from 2 to 16 cylinders in V-formation. Flat engines – like a V design flattened out – are common in small airplanes and motorcycles and were a hallmark of Volkswagen automobiles into the 1990s. Flat 6sare still used in many modern Porsches, as well as Subarus. Many flat engines are air-cooled. Less common, but notable in vehicles designed for high speeds is the W formation, similar to having 2 V engines side by side. Alternatives include rotary and radial engines the latter typically have 7 or 9 cylinders in a single ring, or 10 or 14 cylinders in two rings.

COOLING

Petrol engines may be air-cooled, with fins (to increase the surface area on the cylinders and cylinder head); or liquid-cooled, by a water jacket and radiator. The coolant was formerly water, but is now usually a mixture of water and either ethylene glycol or propylene glycol. These mixtures have lower freezing points and higher boiling points than pure water and also prevent corrosion, with modern antifreezes also containing lubricants and other additives to protect water pump seals and bearings. The cooling system is usually slightly pressurized to further raise the boiling point of the coolant.

IGNITION

Petrol engines use spark ignition and high voltage current for the spark may be provided by a magneto or an ignition coil. In modern car engines the ignition timing is managed by an electronic Engine Control Unit.

ADVANTAGES

i. Cheaper than a diesel engine.

ii. Less maintenance cost.

iii. Easy to construct and repair.

iv. Can be used in light weight vehicles.

v. Smooth, less vibration and better acceleration than a diesel engine.

DISADVANTAGES

i. Less mileage.

ii. Supply of is decreasing and one will petrol supplies will be exhausted.

iii. Price of petrol is increasing everyday.

iv. Burning of petrol affects the environment as it produces carbon.

v. Transport of petrol is dangerous.      

vi. The volatile components of petrol cause smog.
vii. Less durable than diesel engine.

CONCLUSION

                Petrol engines run at higher speeds than diesels, partially due to their lighter pistons, connecting rods and crankshaft (a design efficiency made possible by lower compression ratios) and due to petrol burning more quickly than diesel. Because pistons in petrol engines tend to have much shorter strokes than pistons in diesel engines, typically it takes less time for a piston in a petrol engine to complete its stroke than a piston in a diesel engine. However the lower compression ratios of petrol engines give petrol engines lower efficiency than diesel engines.