Fuel Injection Strategy for Reducing NOx Emissions from Heavy-Duty Diesel Engines Fueled with DME

A new fuel injection strategy is proposed for DME engines. Under this strategy, a pre-injection up to 40% demand is conducted after intake valves closing. Due to high volatility of DME, a lean homogeneous mixture can be formed during the compression stroke. Near TDC, a pilot injection is conducted. Combined fuel mass for the pre-injection and pilot injection is under the lean combustion limit of DME. Thus, the mixture is enriched and combustion can take place only in the neighborhood of sprays of the pilot injection. The main injection is conducted after TDC. Because only about half of the demand needs to be injected and DME evaporates almost immediately, combustion duration for the main injection plus the unburnt fuel in the cylinder should not be long because a large portion of the fuel has been premixed with air. With a high EGR rate and proper timing for the main injection, low temperature combustion could be realized. Under this lean-oxygen and low-temperature combustion, NO_x formation is suppressed. It is believed that with this new fuel injection strategy, NO_x emissions from DME engines could possibly meet the US 2010 emissions standard for NO_x with a simplified aftertreatment system.