Conversion of a Diesel Engine to a Spark Ignition Natural Gas Engine

Tecogen has developed and applied a novel technique for converting turbocharged automotive diesel engines to operate as dedicated spark ignition engines with natural gas as fuel. The conversion process changes the engine cycle to a more-complete-expansion cycle in which the expansion ratio of the original diesel engine is unchanged while the effective compression ratio is lowered, so that enginedetonation is avoided. The converted natural gas engine, with an expansion ratio higher than that normally used for the conventional spark-ignition natural gas engine, offers thermal efficiency at wide-open-throttle conditions comparable to its diesel counterpart. This technique leaves the engine with the original diesel pistons and cylinder head and, therefore, allows field conversion ofexisting vehicle engines. Low exhaust emissions can be achieved when the engine is operated with precise control of the fuel air mixture at stoichiometry with a three-way catalyst.