Fuel Factors Affecting the High-Load Limit of a Temperature Stratified Controlled Auto-Ignition Engine

Factors affecting the pressure rise rate, and consequently the high-load limit, in the sequential ignition of a homogeneous charge in a temperature gradient have been identified. The pressure rise rate decreases with an increase in the magnitude of the temperature gradient and an increase in the sensitivity of the constant volume ignition delay time to temperature. It increases with an increase in the intrinsic reaction rate (i.e., the reaction rate for a charge of uniform composition and temperature). Since the ignition delay time and the intrinsic reaction rate are directly related to fuel properties, the high-load limit is sensitive to fuel selection.

The above three factors are used to explain the high-load limit obtained from a knock limited Controlled Auto-Ignition (CAI) engine with a homogeneous charge operating with three different fuels. The fuel comparisons are made with the engine operating at the same combustion phasing. The fuel ignition delay time and intrinsic heat release rate have been characterized in a Rapid Compression Machine (RCM). Depending on the operating condition, the ranking of the fuel is explained by different factors. As a result, the role of fuel in determining the high-load limit is complex.