Saturday, April 17, 1999
WE are all very familiar with carburettors. They have been around since the first internal combustion engine fired into life.
"Fired" is the correct word. The whole point of the internal combustion engine is to create an explosion, which generates energy, used to drive the car.
The purpose of the carburettor is to feed a mixture of fuel (mostly petrol, as diesel engines do not have carburettors) and air into the cylinder. In the cylinder head there is a spark plug that causes the explosion, and which in turn pushes the piston down. Liquid petrol is fed into the carburettor and exits as a fine spray. The liquid petrol turns gaseous, thanks to the Venturi effect.
Earlier carburettors were the only way to feed fuel to the cylinder. Now, fuel is injected directly into the cylinder head to be fired. Petrol is fed via a nozzle and it exits in a fine gaseous spray. This is called fuel injection. It has been around a long time but only now is it finding favour with the manufacturers of hi-tech engines.
Originally, just one nozzle or injector was used, and it was referred to as the single point fuel injection. Improvements through exhaustive R & D, have led to the mulitipoint fuel injection (MPFI), which seems to be the new norm.
So is the carburettor on the way out? Could be. It is claimed that the MPEI provides greater efficiency in terms of fuel combustion, and controlling pollution. A 1000cc engine with the MPFI gives about 20 km per litre, manufacturers claim. It also needs little or no maintenance. This plus point could also be its weakest link. The quality of fuel is all important to make the injectors work at full efficiency.
The injectors are electrically controlled and monitor the precise amount of fuel-air mixture. This is the reason for the efficiency. There is no wastage.
In the naturally aspirated engine, the mixture is set. It stays the same even when the engine is hot, cold or warm. This causes much wastage of fuel. The manufacturers realised this and were constantly on the lookout for a way to improve the carburettor.
The MPFI evolved. The fuel-air mixture is electronically monitored and the mixture can be varied to always provide the perfect mixture. This control unit is called the ECM (Electronic control module.) Rather than have one carburettor feed the cylinders with the MPFI, each cylinder head has its own individual injector. The ECM monitors the engine temperature, the amount of pressure on the accelerator, the engine r.p.m. and it even varies the input of the mixture. This, the manufacturers claim increases the fuel efficiency, increases engine life, so that it hardly needs maintenance. In short, it stretches the rupee in every direction.
However, carburettors, which are undoubtedly the hardier lot, also hardly need any maintenance.
Carburettors manufactured in the 80s and 90s were already 100 years old but worked perfectly.
I have a carburettor on my Gypsy which in 200,000 km of driving has had to be opened twice. That counts as zero maintenance.
Though the MPFI is going to be the next wave, the carburettor is here to stay.
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