What do you guys think about the new HCCI engine from GM? It's supposed to by more fuel efficient by igniting a mixture of fuel and air and compressing it in the cylinder. Unlike a spark-ignition gas engine or diesel engine, HCCI produces a low-temperature, flameless energy release throughout the combustion chamber. All of the fuel in the chamber is burned simultaneously. This produces power similar to today’s conventional gas engines but uses less fuel. Heat is a necessary enabler for the HCCI process, according to GM. A traditional spark ignition is used when the engine is started cold to generate heat within the cylinders and quickly heat up the exhaust catalyst and enable the HCCI system. GM says HCCI provides up to a 15 percent fuel savings and meets current emissions standards, but didn’t say when it would appear in any of its vehicles.

 

The technology reminds me a lot of the Honda CVCC or stratified charge technology Smokey Yunick was working on in the 1980s. I would like to know what is the compession ratio?

 

 

It uses a lower compression ratio than a diesel but imagine it's higher than spark ignition. A stratisfied charge design is very similar. The CVCC was more or less for emissions but led Honda to more radical designs like VTEC. Here's a good article on the HCCI technology: http://www.autobloggreen.com/2007/08/26/abg-tech-analysis-and-driving-impression-gms-hcci-engine/

I kinda restudied HCCI before writing this.

I knew ahead of time that since HCCI is a compression ignition type engine that to burn gasoline it would need a higher compression ratio than required to burn diesel fuel. Reason diesel is a high cetane fuel where gasoline is a low cetane fuel. Two different animals for 2 different ignition schemes, that being spark ignition and compression ignition.

Anyway I was surprised to see a test done using only 16:1 compression for gasoline. 14:1 was used for diesel. I think the key was warm up ie preheating, using normal spark ignition. I think HCCI has some good merits. Its a tricky process to control though.