Homogeneous Charge Compression Ignition (HCCI) engines operate by auto-igniting a heated fuel/air mixture by engine compression. The advantage of a HCCI engine includes low NOx emission resulting from the short combustion time and greater engine efficiency than a spark ignited engine. Challenges to HCCI engine design include unburned hydrocarbon emissions caused by fuel stratification on internal engine surfaces and auto-ignition timing.

Ambient air is fed through a double wall pipe exhaust and subsequently directed into a pintle regulated Venturi. Fuel is vaporized and mixed homogeneously with air in the Venturi throat. The mixture is homogeneous at all throttle loadings because the pintle flow regulating valve maintains a high velocity at the Venturi throat. Water is injected into the Venturi throat to regulate the air/fuel charge temperature and, consequently, auto-ignition timing for a Homogeneous Charge Compression Ignition (HCCI) engine.