Abstract
A well-known effective way to improve SI engine thermal efficiency is to use, even in small amounts, hydrogen mixed with gasoline. Research has been conducted to investigate and prove that hydrogen addition results in faster flame speed suppressed knock intensity and improved combustion stability. These benefits enable higher compression ratios, higher EGR rates and improved SI engine thermal efficiency.
Fuel reforming is one way to generate hydrogen, using hydrocarbon fuel, exhaust gas steam and heat, hydrogen reformation is achieved using species already available in the internal combustion engines exhaust gas. However, for steam reforming to be valuable, the hydrocarbon conversion efficiency should be above the net gain level at all of the engines operating condition; The fuel used in the reformation process must be more the offset in order to realize a gain in engine efficiency.
This study investigates how the combustion characteristics are affected by the addition of reformed hydrogen in the presence of cooled EGR (CEGR) on a 4 cylinder turbo gasoline direct injection (TGDI) engine. The reforming system design is optimized to increase conversion efficiency and enlarge available reforming zone. Steam to carbon ratio (SCR) is controlled to achieve a sufficient amount of hydrogen and increase the conversion efficiency of the on-board fuel reforming system of the 4 cylinder TGDI engine.
It is in the current research that the available reforming zone is enlarged and the conversion efficiency is increased by system design optimization, and the combustions speed is increased at a range of engine loads when hydrogen from on-board fuel reforming system is supplied into combustion chamber by means of CEGR gas. It is also found that total engine fuel consumption is improved without modification to compression ratio or EGR rate.
