Perfect Combustion, Minimal Emissions
HCCI is the acronym that is expected to revolutionize the automotive industry. It stands for Homogeneous Charge Compression Ignition, a technology with which Bosch researchers intend to combine the advantages of gasoline and diesel engines in a single system: Lower emissions and lower fuel consumption.
An engine’s fuel consumption and emissions are directly influenced by the combustion process. A fuel that burns incompletely is obviously being utilized imperfectly, and unburnt hydrocarbons remain as pollutants. In the direct injection of gasoline or diesel, the fuel is atomized very finely to ensure good combustion. But that’s just one part of the story.
The other is that the nature of the combustion process also influences pollutant emissions. If the fuel jet burns like a flare, nitrogen oxides are formed in the hot peripheral zones while soot is formed in the cooler areas. It’s this kind of inhomogeneous combustion that creates problems. Therefore Bosch researchers are looking for ways of making combustion more homogeneous. One possible method goes like this: The injection system injects a metered dose of gasoline or diesel fuel into the cylinder.
During the ensuing moment, fuel and air throughout the combustion chamber have time to mix, forming a nearly uniform mixture. The piston then compresses the mixture, causing the temperature and pressure to rise until the mixture ignites almost uniformly – with no flame front, no nitrogen oxides and no soot.
That is the theory. The trick is to make it work like that in practice. The total system, including injection, engine and engine management, is highly complex. That is why the scientists at Bosch have to fine-tune all the variables to optimize both fuel consumption and emissions. They are using experiments as well as simulations to design combustion chamber geometries that optimize the processes of homogenization and combustion. And they are investigating the best ignition timing during a cylinder cycle. Another factor that can improve the rate of combustion and reduce exhaust emissions is air management, i.e. the metering and mixing of cold intake air and hot exhaust gases.
Researchers hope that this approach will meet the more stringent future emission limits without the need for costly exhaust after-treatment, such as catalytic converters to reduce nitrogen oxides. After all, the more complex the treatment of raw emissions from the engine, the greater the risk that fuel consumption will also increase.
The other is that the nature of the combustion process also influences pollutant emissions. If the fuel jet burns like a flare, nitrogen oxides are formed in the hot peripheral zones while soot is formed in the cooler areas. It’s this kind of inhomogeneous combustion that creates problems. Therefore Bosch researchers are looking for ways of making combustion more homogeneous. One possible method goes like this: The injection system injects a metered dose of gasoline or diesel fuel into the cylinder.
During the ensuing moment, fuel and air throughout the combustion chamber have time to mix, forming a nearly uniform mixture. The piston then compresses the mixture, causing the temperature and pressure to rise until the mixture ignites almost uniformly – with no flame front, no nitrogen oxides and no soot.
That is the theory. The trick is to make it work like that in practice. The total system, including injection, engine and engine management, is highly complex. That is why the scientists at Bosch have to fine-tune all the variables to optimize both fuel consumption and emissions. They are using experiments as well as simulations to design combustion chamber geometries that optimize the processes of homogenization and combustion. And they are investigating the best ignition timing during a cylinder cycle. Another factor that can improve the rate of combustion and reduce exhaust emissions is air management, i.e. the metering and mixing of cold intake air and hot exhaust gases.
Researchers hope that this approach will meet the more stringent future emission limits without the need for costly exhaust after-treatment, such as catalytic converters to reduce nitrogen oxides. After all, the more complex the treatment of raw emissions from the engine, the greater the risk that fuel consumption will also increase.
The transparent engine is used to study fuel distribution within the combustion chamber.
