Higher Efficiency Gasoline Engine

One of the most tangible ways to help solve the looming energy crisis is to focus on reducing consumption. Delphi, a major automotive parts supplier, has been conducting research aimed at just that - reducing fuel consumption via more efficient engines.

(Delphi's test engine. Credit: Technology Review)

Specifically, the company says it has developed a new gasoline engine that boosts fuel economy by 50%. The design is built around the mechanics of a typical diesel engine, and is made possible by modern advances in valve timing, intake, and exhaust technologies.

How It Works

Delphi's single cylinder test engine operates like a diesel engine using compression-ignition. This means that combustion occurs by compressing air in a cylinder. Compression causes the air to heat to high temperatures, which then vaporizes and ignites fuel when it is injected into the cylinder. This method promotes better fuel efficiency because it allows combustion to take place at higher temperatures.

Typical gasoline engines use a spark plug to ignite the air-fuel mixture after it is compressed in the cylinder (spark-ignition). This is less efficient than compression-ignition because the lower temperatures result in a less-complete combustion. This is why gasoline engines have lower fuel economies than diesel engines.

(Credit: Torque News -->)

The reason gasoline engines have not been designed for the diesel cycle is because gasoline is more volatile than diesel. This makes control of the fuel much more difficult, and autoignition (engine knocking) much more likely, especially while the engine undergoes changes in loads (e.g. acceleration, cruising, idling).

Delphi's solution involves timing three bursts of gasoline into the chamber. This allows the fuel to burn faster to increase efficiency, but slow enough not to induce engine knock or damage. Other strategies, such as re-directing exhaust flow for temperature control and optimizing fuel:air mixtures during combustion, are also incorporated into the new design.

What It Means

Diesel engines can tout higher efficiencies than gasoline engines, but they have their flaws. For one, diesel engines (which vary fuel rather than air to control power) have dirtier fuel emissions than those from gasoline engines. Consequently, diesel engines require more after-treatment to meet exhaust emission standards.

If Delphi's estimates are correct, they will have effectively made an engine with the efficiency of diesel and the emissive properties of gasoline. The technology will also have implications for hybrid technology, either making it obsolete or opening doors for new designs which incorporate both systems together.

The biggest question is whether a full-sized, multi-cylinder version of this design will be effective under the range of loads and speeds typical of operating conditions for most cars. If it is successful, the efficiency gains are a pretty exciting prospect for the transportation industry.

References

Technology Review - Engine Could Boost Fuel Economy by Half