Low-Temp Combustion Could Significantly Aid Gas Mileage

A series of experiments on a one-cylinder gasoline test engine are delivering promising results for research engineers seeking to further improve fuel mileage and emissions.

The initial findings were announced last week at the 2012 SAE World Congress, and are based on a series of experiments by Delphi in conjunction with Hyundai America Technical Center, Wisconsin-Madison University and Wisconsin Engine Research Consultants.

The program, which received a $7.48 million grant from the U.S. Department of Energy, was started back in 2010 with the idea of using the concept of gasoline direct high compression and delayed fuel injection to ignite the mixture instead of a spark similar in concept to a diesel engine, such as the GM Duramax.

By compressing the air/fuel mixture at low temperatures, more efficient combustion is realized, providing significant gains in both fuel economy and emissions reduction.

Through a series of tests conducted using a single-cylinder research engine fitted with different fuel injector designs and intake/exhaust valve timing, the results have shown a low output of exhaust particulate matter and up to a 60-percent improvement in fuel economy over a comparable spark plug equipped engine.

Presenting the findings at last week’s SAE World Congress in Detroit, Mark Sellnau, engineering manager of Advanced Powertrain Technology at Delphi said that so far, “the single-cylinder engine tests of a GDCI combustion system indicated good potential for a high efficiency, low-emissions powertrain.” However, he did also say that, “additional testing and development on a multi-cylinder engine is needed, including cold-starting and transient operation.”

Nevertheless, based on the results so far, the concept looks rather promising and with diesel technology not currently at the forefront of legislative minds in the U.S., the compression ignition combustion gasoline engine could provide motorists in this country with another worthy alternative to pure EVs and gas electric hybrids.

Green Car Congress

  • AP

    Actually, the combustion is not started by “delayed fuel injection”, but by the high temperature and pressure from compression. In diesels, combustion is started by injecting fuel, because initally only air is brought into the cylinder. But here, the air and fuel are already mixed, and combustion only happens when the mixture is compressed enough.

    Also, combustion is not made more efficient by “compressing the air/fuel mixture at low temperatures”. In fact, the high-temperature compression is responsible for starting the burn.

    While this type of engine does burn at a lower peak temperature, it’s because all the air/fuel is burned at once, instead of slowly as in typical engines. This avoids heating and compressing “late-burning” air/fuel mixture to high temps, which is what creates NOx pollutants. This is why they call it “cold combustion.”

    Note that I work at GM as an engineer, but I’m not giving away any secrets. This is in the technical literature.