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The better engine

Last week, we learned how fuel and air are mixed in the required proportion.

india Updated: Aug 27, 2009 11:07 IST
Grease Monkey

Last week, we learned how fuel and air are mixed in the required proportion. To recap, carburettors were invented by Karl Benz at the turn of the last century and have been used since then — only now have Indian bikes been moving slowly towards fuel injection.

Carburettors are inexpensive, they’re light, they won’t have software problems since they’re purely mechanical, and water won’t fry anything in them. If water does get in, simply drain the carb, reconnect fuel from the tank and you’re good to go.

Moving to computers
In the search for faster, more efficient fuel-air mixers, we looked to the same solution as in every other walk of life — computers. Electronic fuel injection was cleaner and faster, and if anything went wrong, you simply hooked up a scanner to the ECU and the computer told you what was wrong, quite like an F1 mechanic and his laptop.

Electronic Fuel Injection (‘EFI’ or simply ‘FI’) systems aren’t as fiendishly complex as a Formula 1 car’s system, although you can’t tinker around with it at home as easily as you can with a carburettor, either. We’ve gone through the components of an FI system last week, so this time we’ll run through them rapidly: fuel pump, injectors, sensors in intake manifold and exhaust, and an ECU that nannies the whole thing.

Indirect vs direct injection
Fuel injection debuted on a production car in the 1950s with the petrol-powered Mercedes-Benz 300SL. Cars today run fuel injection in many different forms. Diesel engines have used indirect injection for a long time, like the first-generation Indian Ford Endeavour did.

This helps reduce engine noise, helps the fuel and air mix better and puts less stress on the related engine components. However, indirect injection also tends to generate a lot of heat that cannot be used constructively — it goes directly to the cooling system that then gets rid of it.

This means that indirect injection is about as efficient as a clerk in a government office. Direct injection thus muscled its way onto the scene — look carefully at Mahindra’s older pickup trucks (some models have ingeniously been named ‘Pik-up’) and you’ll see a sticker proclaiming ‘DID’, which I’ve been told stands for ‘Direct Injection Diesel’.

Today, ‘Di-D’ is a Mitsubishi-patented set of alphabets. Direct injection diesel engines are noisy, but they are a lot more efficient and responsive compared to indirect-injection engines.

The future of engine tech
Diesels have gone a few leaps further with common-rail direct injection, which is a single tube (the ‘common rail’) which carries the fuel under really high pressure, about 1500 -1600 bar. The rail has smaller tubes that go to injectors which inject fuel directly into the cylinder. A single pump is used in a common-rail system, but the Volkswagen group developed the ‘Pumpe Duse’ system in conjunction with Bosch, which has a pump for every injector.

PD is used on the Skoda Laura, the VW Jetta and Passat, and on the Audi A4, except the current generation A4.

PD, or ‘unit injector tech’ allows for greater control over the injection, but as it runs at higher pressures (1700 bar) it can get noisy. However, these engines are slightly more efficient and much more responsive than equivalent common-rail engines.

The VW group is now shutting the door on PD and moving to common-rail technology with the rest of the world as common-rail is a lot quieter and meets ever-tightening emission norms.

It’s a lot cheaper as well, I suspect, since everyone and their uncle is now using it on their diesel powerplants.

Petrol engines have also undergone an epiphany recently — we’ll discuss them next week.

If you have questions or comments for Grease Monkey,
email him at with Auto Tech 101 in the subject line