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Engine experts have dreamt about it, talked about it, and lectured about it, and today – for the first time – General Motors is letting outside parties drive the “most awaited advanced combustion technology” of the last 30 years. 

‘Homogenous charge compression ignition’ technology – or HCCI for short – which debuts today in a Vauxhall Vectra and a Saturn Aura, enables conventional petrol engines to approach diesel-like engine efficiency but does not require the same expensive exhaust after-treatment to reduce emissions that diesel engines need. Not only is the new system adaptable to today’s standard petrol engine architectures and compatible with all commercially-available petrol, it is also compatible with bioethanol E85 fuel. When combined with other advanced technologies such as direct injection, electric cam phasing, variable valve lift and cylinder pressure sensing, HCCI provides up to 15 percent fuel savings, while meeting future emissions standards.

“I remember debating this combustion capability when I was in college,” said Tom Stephens, group vice president, GM Powertrain and Quality.  “It was just a dream then.  Today, using math-based predictive analysis and other tools, we are beginning to see how we can make this technology real.  By combining HCCI with other advanced petrol engine and control technologies we can deliver good fuel savings for consumers.”      

In an integrated engine concept, HCCI along with other enabling advanced technologies approaches the engine efficiency of a diesel, but without the need for expensive lean nitrogen oxide (NOx) after-treatment systems. The engine’s efficiency comes from burning fuel at lower temperatures and reducing the heat energy lost during the combustion process. Consequently, less carbon dioxide (CO2) is released because the vehicle’s operation in HCCI mode is more efficient.

The HCCI-powered concept vehicles – a production-based Vauxhall Vectra, with a modified 2.2L Ecotec four-cylinder engine – drive like conventionally powered vehicles, but offer up to 15 percent improved fuel efficiency compared to a comparable port fuel injected engine. The driveable concept vehicles represent one of the first tangible demonstrations of HCCI technology outside of the laboratory.

An HCCI engine ignites a mixture of fuel and air by compressing it in the cylinder. Unlike a spark ignition petrol or diesel engine, HCCI produces a low-temperature, flameless release of energy throughout the entire combustion chamber. All of the fuel in the chamber is burned simultaneously.  This produces power similar to today’s conventional petrol engines, but uses less fuel to do it.

“Although our development costs for HCCI have been substantial, we have made tremendous strides in bringing this most awaited combustion technology out of the lab and onto the test track with the Vauxhall Vectra and Saturn Aura concept vehicles. Additional development costs, including research and testing programmes are required to make the technology ready for the great variety of driving conditions that customers experience,” said Prof. Grebe.

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