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A new injector has been designed for sequential injection of high-pressure natural gas and a quantity of liquid diesel fuel directly into diesel engine cylinders late in the compression stroke. Injected a few degrees before the natural gas, the pilot liquid fuel auto-ignites and serves, as it burns, to ignite the gaseous fuel which enters the chamber as an underexpanded sonic jet generating high local turbulence. Tests on a single-cylinder two-stroke engine with full electronic control have demonstrated the capability of this fueling method to nearly match conventional diesel engine efficiency over a wide range of load and substantially reduce the emissions of oxides of nitrogen (NOx), particulate mater (PM) and carbon dioxide (CO2).

Impending Environmental Protection Agency (EPA) regulations will place severe limits on exhaust emissions of heavy duty diesel engines for urban bus and highway truck applications. To meet this challenge an intensifier-injector system for natural gas fueling of diesel engines is being developed. The intensifier-injector concept employs electronically-controlled, late-cycle, direct injection of high-pressure natural gas with a pilot quantity of diesel fuel. Preliminary performance and emissions data are presented to indicate the potential for diesel engine efficiencies with reduced emissions with this method of natural-gas fueling.