General Motors, Robert Bosch and Stanford University are developing a cost-effective engine technology that makes petrol engines much more efficient and diesel engines much cleaner, for both conventional and hybrid propulsion systems.

Under a three-year, $US2.5 million programme announced on Wednesday, GM, Bosch and STANFORD researchers will work to accelerate the development of Homogeneous Charge Compression Ignition, or HCCI, which is a research technology that has the potential to dramatically improve the efficiency of petrol and hybrid propulsion systems by more efficiently burning the fuel.

HCCI contributes significantly to a further improvement of the petrol engine’s efficiency by 20%, while achieving near-zero oxide of nitrogen (NOx) emissions and particulates – contributors to ozone depletion and smog.

According to Gary Smyth, director of Powertrain Systems Research Lab, GM Research & Development and Strategic Planning, “It is GM’s goal to develop and demonstrate the viability of HCCI – a clean, efficient combustion process – within the next few years. The joint programme will allow us to expand the scope of controls, sensors, and actuators work beyond what we’re already doing toward this goal.”

This technology is attractive, as HCCI engines have the potential to provide a dramatic increase in fuel efficiency over conventional port fuel-injection spark-ignition engines and can run with diesel-like efficiency, but produce near zero particulates and very low NOx emissions.  “For example,” Smyth said, “petrol engines could achieve 80% of diesel engine efficiency for about 50% of the cost.”

In the HCCI engine, fuel is uniformly mixed with air (hence, “homogeneous charge), as in a spark-ignition engine, but with a higher proportion of air to fuel. Rather than using a spark plug to ignite the air-fuel mixture, however, the mixture is compressed by the piston until rising temperatures inside the chamber ignites it spontaneously – a process similar to that used in a diesel engine (hence, “compression ignition”), but at a much lower temperature.  The lower combustion temperature combined with the high ratio of air to fuel, known as lean operation, virtually eliminates NOx emissions and lowers throttling losses, which leads to a significant boost in fuel economy.

Despite the advantages offered by HCCI engines, controlling HCCI combustion in the real-world environment versus the lab environment is a major hurdle for its commercialisation, according to Patrick Popp, director of Electrical & Controls Integration Lab, GM Research & Development and Strategic Planning. “For it to be successful, HCCI will require development of advanced control technology and systems to make it robust. The development of critical sensors and actuators, along with control systems, will allow us to maximize the performance of the combustion system during transient operation, and comprehend the variation in fuels found around the globe.”

Rolf Leonhard, executive vice president, Engineering Petrol Systems Division, Robert Bosch GmbH, believes that HCCI could be a very promising technology for future generations of petrol engines. “It is simply a better way to combust, providing large gains in fuel economy,” Leonhard stated. “Due to the ‘cold’ HCCI combustion, engine raw emissions can be drastically reduced, offering the potential to meet emission standards with a cost effective three-way catalyst. However, stable and satisfactory operation of an HCCI engine is not possible without further development and sophistication of sensors, actuators and feedback control systems. The goal at the end of the day will be to suggest a complete engine controls solution that is both robust and cost effective.”

The Bosch Research and Technology Centre (Bosch RTC) in Palo Alto, CA, in conjunction with Stanford, have already been working on advanced system technology for HCCI combustion control. During the same timeframe, GM’s global research and development team, in cooperation with a number of other universities and suppliers in both North America and Europe, has developed an HCCI combustion system concept, base engine architecture, and operating strategy that allows the operation of HCCI over a broad engine speed and load range.

The interaction between industrial and academic researchers is central to this project. ”Stanford’s real strength is the ability to offer new perspectives on problems,” said Chris Gerdes of Stanford University. “In the case of HCCI, we have demonstrated how the physics of combustion can be used as a model for the control system, tightly linking the fields of combustion and control.

According to Smyth, the joint programme nicely blends the two company’s needs, as GM explores the potential commercial implementation of HCCI engines, and Bosch strives to develop the technologies critical to the manufacture of key HCCI sensors and actuators. “We bring engine, combustion and control system experience along with key operating strategies,” Smyth said.

“Bosch and Stanford supply control system experience along with knowledge associated with critical sensors and actuators.”