How your car works - Internal Combustion Engine

What's the difference between Petrol and Diesel?
The most popular form of propulsion for cars this century has to be the petrol internal combustion engine. It has been dominant for approximately 100 years with very little competition, until now when in fact we are also seeing significant numbers of diesel vehicles on our roads. Although more recently, a question mark hangs over the Diesel's emissions. Called 'Particulates', these remain airborne and are thought to be harmful to health.

Petrol Internal Combustion Engines
Energy density relates directly to how far you can travel on a quantity of fuel. For example, if 1 gallon of petrol gives you 35 miles of distance travelled, 1 gallon of Diesel will give you 41 miles of distance travelled. Whereas the same gallon of Liquid Propane Gas would typically give 28 miles in distance travelled. Petrol, it is clear, has long been the most suitable fossil fuel with which to propel the car. Its high energy content simply means that a little goes a long way. To understand how petrol powers the car's engine, it is necessary to understand how the internal combustion engine works. The term 'internal combustion' basically means that the fuel is burnt inside a combustion chamber within the engine. A combustion chamber is an area inside the cylinder block and cylinder head (that is sealed and isolated from the rest of the engine and referred to as the cylinder) where a fuel and air mixture is introduced and ignited. As in the diagram shown here, the engine is made up of many different components.

The Four Stroke Cycle
Most cars have a '4 stroke' engine with 4 cylinders. This means that the engine has separate stages of operation within a complete revolution or cycle of the crankshaft.

1. Induction: This is when the fuel and air mixture is drawn into the cylinder by the piston going down and producing suction.
2. Compression: This is the stage when the fuel and air mixture is compressed and forced to the top of the cylinder ready for ignition.
3. Ignition: This is when the fuel and air mixture is ignited by the spark plug. The piston is then forced downwards, turning the crankshaft and generating the propulsion for the engine.
4. Exhaust: This is when the exhaust gases (after the fuel is burnt) exit the engine.

Diesel Internal Combustion Engines
A Diesel engine is essentially the same as a petrol engine but it burns a different type of fuel. Diesel is named after its inventor Rudolf Diesel, a German who first developed this type of propulsion unit back at the turn of this century. Diesel engines have mainly been used in taxis and buses since the 1950s because of their increased power - especially high torque output - and their reliability. They tend to be noisy and smelly compared to a petrol engine but are more fuel economical. The difference between a petrol and a diesel lies in the way the fuel is introduced into the engine and ignited. The compression stroke only compresses air and not fuel. On the ignition stroke (there is no need for a spark as in the petrol engine) the air is compressed to a very high pressure and this generates enormous heat which then ignites the fuel that is injected into the combustion chamber at that precise moment of maximum pressure. A diesel engine thus has a far higher "compression ratio" than does a petrol engine (Diesel engines usually 20 to 1, petrol engines typically 9 to one).

Caring For Your Petrol Engine

• The engine is the most important part of your car. Generally, a petrol engine is good for 150,000 miles without any problems. To ensure however that your engine gives you long and trouble-free service, it is essential that preventative maintenance is carried out. Your local Unipart Car Care Centre should really service your car at least once a year and in the process check that everything is operating correctly within the engine. On many engines typical maintenance and service replacement items are fanbelt, power assisted steering belt, camshaft drivebelt, spark plugs, oil filters and air filters.
• Always keep an eye on the fluid levels under the bonnet. Check the engine oil level at least once a week. Check the coolant level in the radiator at the same time and top up if necessary. Only check these fluid levels when the engine is cold and on a level surface. Always refer to your car's handbook for instructions on how to do this correctly.
• Never drive the car with either the oil pressure or coolant warning lights on. If you see these warning lights stop the engine immediately and investigate the problem. If ignored, the engine could fail prematurely.

Caring For Your Diesel Engine

• A Diesel engine will normally last longer. If correctly maintained, in the region of 250,000 miles without major problems. But the same precautions have to be observed as for the petrol engine. Most important and very simple is to change the engine oil at least once every 6 months or 6000 miles. Your local garage is able to service your car at least once a year and check that everything is operating correctly within the engine.
• As with the petrol engine, always allow the engine to warm up for a couple of minutes before driving when cold. This will increase the engine's life and decrease maintenance costs. A cold engine wears quicker than a warm engine.