I am working in Professor Kusaka’s laboratory on a joint project with an automobile manufacture for development of an engine that uses a novel combustion system. This is an engine in which combustion takes place by homogeneous charge compression ignition (HCCI).
The engines generally in use today use either gasoline or diesel fuel. The former produces low emissions at the expense of poor fuel efficiency, while the latter provides good fuel efficiency but with a higher level of emissions. The HCCI combustion system combines the advantages of these two systems to resolve the shortcomings of both. A number of companies are conducting research into HCCI engines, and it is expected that they will come into practical use sometime between 2020 and 2030.
Every engine works by igniting a mixture of fuel and air.
In today’s gasoline engines, a pre-mixed combination of fuel and air is ignited by spark plug. The problem with this system is that time is required for combustion to expand spherically through the mixture from the center of ignition, which is the spark plug. This lag is what accounts for the poor fuel efficiency of such engines.
On the other hand, instead of using spark plugs, diesel engines work by super-heating a volume of air through compression with a piston, and then injecting diesel fuel which ignites spontaneously upon injection. This is possible because diesel fuel ignites at relatively low temperature. However, when diesel fuel is injected into the cylinder, variations in density are produced, and soot results from the denser regions.
With the HCCI combustion system, a mixture of gasoline and air is compressed and spontaneous combustion is induced by a chemical reaction, making it possible to optimize fuel efficiency while minimizing environmental consequences. However, it is hard to induce spontaneous combustion in gasoline, which presents a challenge with regard to controlling the timing of ignition.