Direct injection for dual fuel stratification (DDFS): Improving the control of heat release in advanced IC engine combustion strategies

Wissink, M. L. Direct Injection for Dual Fuel Stratification (DDFS): Improving the Control of Heat Release in Advanced IC Engine Combustion Strategies. University of Wisconsin-Madison, 2015.

Low temperature combustion (LTC) strategies can achieve high thermal efficiency with low engine-out NOx and soot emissions. However, controlling the timing and rate of heat release under LTC conditions in a consistent manner has proven to be difficult, and emissions of CO and unburned hydrocarbons (HC) are high. Several fueling strategies have been developed to create stratification of equivalence ratio and ignition delay such that heat release is retarded and lengthened, but these strategies typically result in a trade-off between efficiency and noise, a narrow operating range, or impractical boundary conditions, and the issue of high CO and HC emissions remains. In this research, a new strategy is proposed in which two fuels with different autoignition characteristics are introduced to the cylinder via multiple direct injections, allowing for greater control and range of reactivity and equivalence ratio distribution, as well as the possibility of mixed combustion modes. A series of experiments detail the development of the fueling strategy, an exploration of the parameters contributing to noise and emissions, a pathway to practical high-load operation, and a comparison to existing LTC strategies. By direct-injecting two fuels, it is possible to gain a new level of control over the shape and stability of the heat release event, along with the ability to combine and exploit the practical benefits of existing combustion strategies in a manner that was previously impossible.