The Washington Times - June 20, 2008, 10:02AM

 

The internal combustion engine isn’t obsolete yet

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Most people connected to the auto industry - engineers, marketers, dealers, safety experts and yes, automotive writers - agree that passenger vehicles of the future will be electrically powered. Whether the source of electricity is a battery, fuel cell or other storage device the thing that actually turns the wheels will be an electric motor. Electric motors are the most reliable and efficient propulsion devices ever engineered by man, and anyone involved in designing cars would love to transition to them now.

Unfortunately “now” isn’t the future and there are some major engineering and infrastructure challenges that need to be overcome before the future arrives. So when will that be, you might ask? The best guesses at the present time say that electric propulsion won’t be the dominant technology for about 40 years. Meanwhile, several “bridge” technologies such as hybrids, plug-in hybrids, compressed natural gas, alternative fuels, lithium-ion batteries and fuel cells will slowly spread in the marketplace.

Still, it’s a safe bet that the internal combustion engine will continue to power the majority of passenger vehicles for a long time. Over the past thirty years combustion technology research has resulted in the cleanest, most fuel-efficient gasoline engines ever, thanks to computer control, metallurgy and advances in fuel injection. Engines are getting smaller and smaller while providing greater performance than their predecessors and there are still more new technologies coming on line that will squeeze further efficiencies. Exotic-sounding terms like “closed loop combustion process” and “homogenous charge compression ignition” will become as familiar as “fuel injection” and “electronic ignition” are today.

I recently drove an engineering prototype GM car equipped with Homogenous Charge Compression Ignition (HCCI) and found it a fascinating approach. The idea behind HCCI is to make a gasoline-fueled engine run under certain circumstances like a diesel-fueled engine. The difference between the two types of engine is compression ratio. In gas engines the fuel/air mixture is compressed to a maximum of 12 to 1 and then ignited with a spark plug. Diesel engines typically have compression ratios of 22 to 1 and the heat generated in compressing the fuel/air mixture ignites it. Because diesel engines get more power out of each combustion cycle they are about 30% more fuel efficient than gas engines of the same size.

It’s normally not possible to burn gas in a diesel engine because it will pre-ignite (due to heat of compression) while the piston is coming up, causing internal damage. If, however, a gas engine can be designed to run like a diesel - at least some of the time, under specific load conditions - fuel efficiency can be increased and engine size decreased without losing performance. Using an electronically controlled auto-ignition system and varying valve overlap (trust me, you don’t want to sit through an explanation of this term!) GM engineers have successfully created an HCCI engine that works sometimes like a gas engine and sometimes like a diesel. Fuel consumption is reduced by 15% over an equivalent gas engine.

I found the car to drive like any “normal” car. At times the engine’s exhaust note sounded like any other car and at other times there was a pronounced diesel-clacking, but the engineers made it clear that these oddities would be easily eliminated in production vehicles through exhaust system technology.

Approaches like this are sure to keep the internal combustion engine in common use for the next few decades. Engines will continue to get smaller because power outputs won’t be compromised. The old adage, “there’s no replacement for displacement” is no longer true, so I think within the next 10 years the V8 engine will only be found in trucks and high performance cars.  V6 engines won’t be far behind, either. We won’t need them.