Utilizing Static Autoignition Measurements to Estimate Intake Air Condition Requirements for Compression Ignition in a Multi-Mode Engine - Engine and RCM Experimental Study

A multi-mode operation strategy, wherein an engine operates compression ignited at low load and spark ignited at high load, is an attractive way of achieving better part-load efficiency in a light duty spark ignition (SI) engine. Given the sensitivity of compression ignition operation to in-cylinder conditions, one of the critical requirements in realizing such strategy in practice, is accurate control of intake charge conditions - pressure (P), temperature (T) and equivalence ratio (φ), in order to achieve stable combustion and enable rapid mode-switches. This paper presents the first of a two part study, correlating ignition delay data for five RON98 gasoline blends measured under engine-relevant operating conditions in a rapid compression machine (RCM), to the cylinder conditions obtained from a modern SI engine operated in compression ignition mode. The overall trend in reactivity for the fuels was found to be similar in the two devices, although the compressed charge in the engine did not correlate directly with the constant ignition delay trajectories in the P-T diagram. However, positive correlation was found between the compressed pressure at constant ignition delay in the RCM and the intake boosting requirement for the engine to maintain constant combustion phasing. This suggests that static auto-ignition delay measurements can be utilized to estimate intake manifold conditions towards enabling combustion phasing control in a gasoline compression ignition engine.