Investigation of Steady-State RCCI Operation in a Light-Duty Multi-Cylinder Engine Using “Dieseline” 2017-01-0761
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 NOx 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 operating conditions with custom designed, 15.3:1 compression ratio, pistons. Experiments were conducted using mixtures of gasoline and diesel, i.e., “dieseline”, as the high reactivity fuel and a comparison to gasoline/diesel RCCI combustion is made. The tests 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 direct-injected (DI) fuel mixture to in turn reduce the need for a second fuel.