Currently the two main types of engines used all over the world are gasoline Spark-Ignition (SI) engines and diesel engines. For all those who are not to proficient in engine mechanics here is a crash course. In a gasoline SI engine combustion begins when a mixture of fuel and air is ignited by the spark plug, the diesel engine on the other hand does not make use of a spark plug. In a diesel engine combustion begins when fuel is injected into hot, highly compressed air. (That’s why diesel cars often have an engine heater)
Now researchers know that if they can remove the spark plug from the gasoline engine they can save some precious fuel, but how can this be accomplished...? The answer is an HCCI or Homogeneous Charge Compression Ignition engine. In this engine well mixed fuel and air are compressed until the point they spontaneously ignite at multiple points throughout the combustion chamber. This engine has been developed by researchers at MIT who hope to curb the global oil demand with this engine.
This mode-switching capability could appear in production engines within a few years improving fuel economy by several miles per gallon. The homogeneous combustion of fuel in HCCI engine offers some advantages, in both SI and Diesel engines the fuel must burn hot so that the flame spreads throughout the chamber before a new charge enters the cylinder. In an HCCI engine since the fuel mixture spontaneously ignites due to compression there is no need for a quickly spreading flame because the combustion itself occurs all through the cylinder. As a result the combustion temperatures can be lowered so the emissions of nitrogen pollutants are lowered. The combustion also reaches all parts of the chamber so no fuel is left in the chamber when the cycle ends, which further reduces the amount of soot emitted from the exhaust.
Like all other researches this one too has a dark side. It is difficult to control exactly when ignition might occur in an HCCI engine and if the ignition does not start at the right time the engine might not run right. Ignition in an HCCI engine depends on two main factors that are the temperature of the mixture and the details of the fuel that is being injected. Both these factors account for major problems because none of them can be easily predicted.
To sort out this problem researches now have developed a new hybrid technique. Temperature sensors are mounted in the engine, which determine the time when the SI engine should stop working and the HCCI engine should take over. This mechanism works in tandem and ensures that HCCI engine should work for most of the time. When calculated it was found that HCCI engine works for almost 40% of the time. This means a gallon of fuel in your car will at most last for a few more miles. However, if this is put together it accounts for the savings of a more than a million gallons of oil in the U.S.
If all goes according to plan then we might see these engines in all upcoming models of cars within the next few years.
Via: Physorg
