Development of a two stroke direct injection jet ignition compressed natural gas engine

Alberto A. Boretti, Shuheng Jiang


A traditional two stroke engine with crankcase scavenging also adopting exhaust red valve and lamellar intake is modified to accommodate a high pressure CNG direct injector and has the traditional spark plug replaced by a jet ignition device of same thread. The jet ignition device is a pre-chamber accommodating a gasoline GDI injector operated with CNG and an 8 mm racing spark plug. The jet ignition pre-chamber is connected to the main chamber through calibrated orifices. The CNG is injected after the exhaust post closes. The GDI injector operated with CNG introduces a slightly rich amount of fuel in the pre-chamber. The spark plug discharge initiates the pre-chamber combustion that then propagates to the main chamber though multiple jets of high energy partially burned hot combustion products that quickly ignite the main chamber mixtures. The CAD design of the engine including the jet ignition device is discussed in details. The CAE model of the engine is shown to produces efficiencies well in excess of 35% in the area of best operation. The load is controlled by finely tuning the injection and ignition events a reduced pollution and increasing the overall air-fuel ratio. The solution offer the opportunity to produce an efficient alternative to four stroke engines with improved power density running an alternative fuel having larger availability and better combustion properties and  reduced pollution than traditional diesel and gasoline fuels.  


2 stroke, direct injection, jet ignition

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