Homogeneous charge compression ignition dual fuel engine and method for operation

Abstract

A Homogenous Charge Compression Ignition (HCCI) engine and operating method having ignition timing controlled on a cycle to cycle basis by adding to a primary fuel, which is typically greater than 95% and is a gas such as natural gas with a relatively slow burn rate, varying amounts of high cetane number fuel, typically diesel fuel, before or early in the compression stroke. The amount of high cetane fuel that is injected depends on engine speed and load, and is selected to insure that combustion is phased properly with crankshaft position. The ignition delay is thus controlled substantially independently of the burn duration, which is controlled by varying the amount of Exhaust Gas Recirculation (EGR) in conjunction with the air to fuel ratio so as to maintain a near constant crank angle burn duration over a wide range of engine speeds. Because of the relatively slow burn rate of the natural gas after ignition, relatively low EGR levels and high boost levels are practical with the subject HCCI engine so that its power density is greater than that of previous HCCI engines. The load and speed of the subject HCCI engine may be controlled over a wide range by varying the overall air to fuel ratio or the boost pressure. The high cetane liquid fuel may be injected together with the gas and early in the compression stroke so that the gas atomizes the liquid upon injection.