In an attempt to increase efficiency and lower critical and highly regulated emissions (i.e., NOx, PM and CO2) many advanced combustion strategies have been investigated. Most of the current strategies fall into the category of low temperature combustion (LTC), which allow emissions mandates to be met in-cylinder along with anticipated reduction in cost and complexity. These strategies, such as homogeneous charge compression ignition (HCCI), premixed charge compression ignition (PCCI), partially premixed combustion (PPC) and reactivity controlled compression ignition (RCCI), use early injection timings, resulting in a highly lean charge with increased specific heat ratios to improve thermal efficiency and reduce PM emissions. Lower combustion temperatures also avoid the activation of NOx formation reactions. However, the lean air/fuel ratio decreases fuel oxidation rates of CO and HC and, due to longer ignition delays with high peak pressure rise rate (PPRR) and heat release rates (HRR), confines the engine?s operating loads and speeds. A strategy to reduce these negative effects of LTC is RCCI, which generally uses two fuels with different reactivities in order to optimize ignitability and equivalence ratio stratification. It has demonstrated improvements in efficiency and low NO x and PM emissions by utilizing in-cylinder fuel blending, while the simultaneous optimization of fuel reactivity results in increased engine operating space.
The current work investigates Reactivity Controlled Compression Ignition (RCCI) combustion in a light-duty multi-cylinder engine over steady-state and transient operating conditions using also fast exhaust sampling emissions equipment for UHC, NO and PM measurements. A ?single-fuel? approach for RCCI combustion was studied using port-injected and direct-injected (DI) cetane improved gasoline with custom designed, 15.3:1 compression ratio, pistons. In addition, experiments were conducted using mixtures of gasoline and diesel, i.e., ?dieseline?, as the high reactivity fuel. The experiments were performed over a broad selection of ?ad hoc? load and speed points in order to examine performance and emission effects of a less reactive DI fuel mixture to in turn reduce the need for a second fuel.
This work also helps to demonstrate the requirements for high levels of boost in a multi-cylinder engine during RCCI operation. Comparisons were also made to an HCCI/GCI like combustion strategy using similar gasoline/diesel fuel blends.