Researchers at MIT working on a new fuel efficient engine

Researchers at MIT are working on a new fuel-efficient engine that may help to bring down global fuel consumption. Researchers have demonstrated how ordinary spark ignition engine can move to a spark-free operating mode that is fuel efficient and just as clean. The new engine is called HCCI (homogeneous charge compression ignition).

hcci engine

In gasoline SI (spark ignition) engines, combustion begins when the spark plug ignites a mixture of fuel and air. Combustion in diesel engines begins when fuel is injected into hot, highly compressed air. HCCI combines the best of both worlds; well-mixed fuel and air are compressed until combustion occurs at multiple points throughout the chamber. This leads to lower combustion temperatures, which in turn lead to lower emission of nitrogen oxides (NOx).

In both, the SI and the diesel engines, it must be ensured that fuel burns hot so that flames spread rapidly through the combustion chamber before the next 'charge' enters. Such problem is non-existent in an HCCI engine because combustion occurs simultaneously at multiple points throughout the chamber. Besides, unlike the SI engine, the HCCI engine does not require 'just enough air' to burn fuel. Therefore, power is not wasted in constraining the incoming air when the fuel input is decreased to reduce power.

The HCCI technology is still in its infancy, and there are some problems associated with it. Controlling the timing of ignition in an HCCI engine is a Herculean task. If the timing is not accurate, the engine will not run right. Ignition timing in an HCCI engine depends on two factors: the temperature of the mixture, and the detailed chemistry of the fuel. Both of these are hard to predict and difficult to control.

Though the HCCI runs well in the laboratory, its performance in the real world is not very predictable at this point of time. A good deal of research has gone in making the engine run in either SI mode or HCCI mode. Range of conditions suitable for the HCCI engine is much smaller than those for the SI engine.

Taking cue from their study, researchers developed an engine that would normally run in SI mode but switch to HCCI whenever possible. Assuming the fuel remains constant, a temperature sensor determines whether the next cycle should be SI or HCCI. Simulated results say that such engine would work in HCCI mode for nearly 40% of the time in an urban setup.

Researchers say this may give an increased fuel efficiency of a few miles per gallon. Admittedly, it's not a very impressive figure, but if all the cars in the USA give a few extra miles per gallon, it could translate into a saving of a million barrels of oil per day.

Good fuel efficiency automatically translates into lower pollution. If this engine's cost is not at the ceiling, it could very well power vehicles in the near future, and save lots of oil every day.

Via: MIT