Typical dual fuel engines operate at relatively low gas pressures (e.g., 100-200 PSI), making in-cylinder injection difficult with traditional nozzle designs. In these engines, the gaseous fuel is mixed with air via fumigation or port injection to provide a homogeneous mixture for a small liquid diesel pilot injection to ignite. In other words, a compression ignited small diesel injection is used to ignite a homogeneous mixture of gaseous fuel and air in the individual cylinders. This approach can create a challenge to control hydrocarbon slip into the exhaust due to fractional amounts of gaseous fuel that are present in the crevice volumes of the combustion chamber. Co-owned U.S. Patent Application Publication No. U.S. 2012/0187218 shows a dual fuel engine alternative in which relatively high pressure gaseous fuel is injected directly into the engine cylinder.
The present disclosure is directed toward one or more of the problems set forth above.