Spark-free, Fuel-efficient Engines On The Way

[Aurora]

http://www.sciencedaily.com/releases/20 ... 175256.htm

Science Daily - 23/07/07



In an advance that could help curb global demand for oil, MIT researchers have demonstrated how ordinary spark-ignition automobile engines can, under certain driving conditions, move into a spark-free operating mode that is more fuel-efficient and just as clean.

The mode-switching capability could appear in production models within a few years, improving fuel economy by several miles per gallon in millions of new cars each year. Over time, that change could cut oil demand in the United States alone by a million barrels a day. Currently, the U.S. consumes more than 20 million barrels of oil a day.

The MIT team presented their latest results on July 23 at the Japan Society of Automotive Engineers (JSAE)/Society of Automotive Engineers (SAE) 2007 International Fuel and Lubricants Meeting.

Many researchers are studying a new way of operating an internal combustion engine known as "homogeneous charge compression ignition" (HCCI). Switching a spark-ignition (SI) engine to HCCI mode pushes up its fuel efficiency.

In an HCCI engine, fuel and air are mixed together and injected into the cylinder. The piston compresses the mixture until spontaneous combustion occurs. The engine thus combines fuel-and-air premixing (as in an SI engine) with spontaneous ignition (as in a diesel engine). The result is the HCCI's distinctive feature: combustion occurs simultaneously at many locations throughout the combustion chamber.

That behavior has advantages. In both SI and diesel engines, the fuel must burn hot to ensure that the flame spreads rapidly through the combustion chamber before a new "charge" enters. In an HCCI engine, there is no need for a quickly spreading flame because combustion occurs throughout the combustion chamber. As a result, combustion temperatures can be lower, so emissions of nitrogen pollutants are negligible. The fuel is spread in low concentrations throughout the cylinder, so the soot emissions from fuel-rich regions in diesels are not present.

Perhaps most important, the HCCI engine is not locked into having just enough air to burn the available fuel, as is the SI engine. When the fuel coming into an SI engine is reduced to cut power, the incoming air must also be constrained--a major source of wasted energy.

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[mikepepler]

Good idea, and lots of car companies have been working on it. Not a silver bullet though, which is probably what some people out there will think.