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The internal combustion engine: not dead yet Add to ...

According to such respected firms as J. P. Morgan, PricewaterhouseCoopers and Nomura, 70 per cent of all new vehicles sold in 2020 will be powered by an internal combustion engine. While there is considerable coverage of, and interest in, electric and fuel cell vehicles, there is obviously a lot of life in the old IC engine yet.

There are two types of internal combustion engine, compression ignition (diesel) and spark ignition (gasoline).

Diesel engines work on the principle of compressing the fuel-air mixture to the point it self-ignites due to the heat caused by that compression. It requires a special fuel - diesel - which is inherently less refined or "clean" than gasoline.

Amazing progress has been made in cleaning up diesel fuel by reducing the sulphur content at the refinery and treating exhaust gases. However, until even cleaner diesel fuel is available here as it is in Europe, diesels will likely continue to be a distant second choice for the average consumer despite the fact they squeeze more power and mileage out of a given unit of fuel.

The modern spark-ignition IC engine bears little resemblance to its forbears other than the fact pistons are pushed down by an explosion, turning a crankshaft and ultimately the drive wheels. The biggest changes have come in the way fuel is introduced into the combustion process and how and when a spark is introduced.

In older engines, gasoline was mixed with air in a carburetor. A nozzle or jet of a particular size determined how much fuel was introduced and the amount of throttle opening determined the amount of air involved. Generally speaking, one unit of fuel for every 15 units of air.

The number of throttle bodies or "barrels" varied according to the size and power requirements of the engine. A single barrel "carb" would suffice for an entry-level four- or six-cylinder engine, two-barrel carburetors were common with base V-8 engines and four-barrels for performance-oriented V-8s. Some used a trio of two-barrel carburetors and there were even those with a pair of four-barrel carburetors - each of the individual barrels more than five centimetres in diameter.

These devices could be tuned only by varying the size of the jets used to spray fuel into the carburetor. When the engine was cold, a choke or flap was used to reduce the amount of air introduced, raising the ratio of fuel to air or making the mixture richer.

Carburetors were not exactly fuel-efficient, either in terms of mileage or exhaust emissions. A great deal of the fuel introduced in the carburetor remained unburned and exited the exhaust pipe as a cloud - sometimes visible - of pollution.

The next step in IC engine evolution was the fuel injector. First came a single injector, which squirted fuel into the throttle body or barrel. A flap continued to vary the amount of air mixed with the fuel. This resulted in improved efficiency, especially in terms of emissions.

Next up were multiple injectors - one for each cylinder. A controlled amount of fuel was sprayed into the intake manifold upstream of the intake valve(s) where it mixed with air before entering the combustion chamber.

As electronics became more powerful and sophisticated, so did fuel injection systems. The main gains have come from injecting fuel directly into each individual combustion chamber. Sophisticated electronics and cleaner fuel has allowed engineers to precisely time the point in the combustion process at which the fuel is injected and when the spark is introduced - approximately 125 times every second in a six-cylinder engine running at only 2,500 rpm.

Variable valve timing is becoming common - the point at which the intake valves open to introduce air and when the exhaust valves open to expel spent gases can be adjusted through various operating conditions and speeds. Cylinder deactivation allows some to be shut down when not needed.

High-pressure injection through as many as six orifices in each injector allows the fuel to be positioned precisely within the combustion chamber for maximum combustion and thus effect when ignited.

That ignition itself is now more precisely timed and powerful than could have been imagined a decade ago. It now can involve multiple sparks per ignition event - one when the fuel-air mixture is first introduced and the piston is on its way up, a second at what would be considered a normal time when the piston is at or near top dead centre and a third when the piston is going back down to ensure all the gases are spent.

What's next? Variable compression ratios, even leaner combustion, improved thermal management and engine shutdown when the vehicle is a rest, combined with eight- to 10-speed transmissions will all be employed in the search for more mileage and fewer emissions.

There's life in the old IC engine yet.

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