Engine Could Boost Fuel Economy by Half

Engineerblogger
May 17, 2012

Trial run: Delphi researchers tested a new combustion strategy in this single-cylinder test engine. Credit: Mark Sellnau, Delphi

Delphi, a major parts supplier to automakers, is developing an engine technology that could improve the fuel economy of gas-powered cars by 50 percent, potentially rivaling the performance of hybrid vehicles while costing less. A test engine based on the technology is similar in some ways to a highly efficient diesel engine, but runs on gasoline.

The company has demonstrated the technology in a single-piston test engine under a wide range of operating conditions. It is beginning tests on a multicylinder engine that will more closely approximate a production engine. Its fuel economy estimates suggest that engines based on the technology could be far more efficient than even diesel engines. Those estimates are based on simulations of how a midsized vehicle would perform with a multicylinder version of the new engine.

The Delphi technology is the latest attempt by researchers to combine the best qualities of diesel and gasoline engines. Diesel engines are 40 to 45 percent efficient in using the energy in fuel to propel a vehicle, compared to roughly 30 percent efficiency for gasoline engines. But diesel engines are dirty and require expensive exhaust-treatment technology to meet emissions regulations.

For decades, researchers have attempted to run diesel-like engines on gasoline to achieve high efficiency with low emissions. Such engines might be cheaper than hybrid technology, since they don't require a large battery and electric motor.

In conventional gasoline-powered engines, a spark ignites a mixture of fuel and air. Diesel engines don't use a spark. Instead, they compress air until it's so hot that fuel injected into the combustion chamber soon ignites. Several researchers have attempted to use compression ignition with gasoline, but it's proved challenging to control such engines, especially under the wide range of loads put on them as a car idles, accelerates, and cruises at various speeds.

Delphi's approach, which is called gasoline-direct-injection compression ignition, aims to overcome the problem by combining a collection of engine-operating strategies that make use of advanced fuel injection and air intake and exhaust controls, many of which are available on advanced engines today.

For example, the researchers found that if they injected the gasoline in three precisely timed bursts, they could avoid the too-rapid combustion that's made some previous experimental engines too noisy. At the same time, they could burn the fuel faster than in conventional gasoline engines, which is necessary for getting the most out of the fuel.

They used other strategies to help the engine perform well at extreme loads. For example, when the engine has just been started or is running at very low speeds, the temperatures in the combustion chamber can be too low to achieve combustion ignition. Under these conditions, the researchers directed exhaust gases into the combustion chamber to warm it up and facilitate combustion.

Mark Sellnau, engineering manager of advanced powertrain technology at Delphi Powertrain, says the engine could be paired with a battery pack and electric motor, as in hybrid cars, to improve efficiency still more, although he notes that it's not clear whether doing that would be worth the added cost.

Source: Technology Review