An HCCI engine ignites an air/fuel mixture by compressing it in the cylinder at low temperature, instead of using a spark plug. The ignition is spontaneous and does not propagate as a flame front. In a gas engine, the ignition is generated from a spark plug, and in a diesel engine, there are multiple flame fronts.
The concept of HCCI technology was introduced three decades back, but advancements took place in the past couple of years when major automakers and research groups across the world started working on building prototypes.
Why HCCI?
- HCCI's primary advantage is more favorable fuel consumption, or better MPG, and generating inherently low emissions. The power produced in an HCCI engine is similar to spark ignition (SI) gasoline engines.
- An HCCI engine, when combined with other advanced technologies, can provide up to 15 percent greater fuel economy than a comparable, non-HCCI engine by using the compression combustion process that operates at a much lower temperature than diesel combustion.
- HCCI combustion takes place at lower temperatures helping to reduce NOx emissions. A diesel HCCI set up emits 30 percent of the NOx that a conventional diesel engine emits, which reduces the necessity of exhaust aftertreatment. By comparison, gas engines have inherently lower NOx emissions, and therefore still more aftertreatment is required for diesels to reduce NOx to the level of gasoline engines.
- The technology is compatible with a wide variety of fuels, such as biofuels, diesel, gasoline, and E85 (ethanol). GM's findings reveal that ethanol is a suitable fuel for auto ignition that offers high octane with no smoke-producing tendency. In addition, ethanol produces easier combustion with low carbon accumulation.
