Effects of Injector Included Angle on Low-Load Low Temperature Gasoline Combustion Using LES

Abstract

<div class="section abstract"><div class="htmlview paragraph">A novel advanced combustion strategy that employs the kinetically controlled compression ignition of gasoline whose autoignition is sensitive to fuel concentration is termed Low Temperature Gasoline Combustion. The LTGC method can achieve high thermal efficiency with a commercially available fuel while generating ultra-low soot and NO_x emissions relative to the conventional combustion modes. At high loads, a double direct injection (D-DI) strategy is used where the first injection generates a background premixed charge while a second compression stroke injection controls the level of fuel stratification on a cycle-to-cycle basis to manage the heat release rates. With lower loads, this combustion performance of this D-DI strategy decreases as the background charge becomes increasingly lean. Instead, a single direct injection (S-DI) is used at lower loads to maintain an adequate combustion efficiency. But the distribution of fuel with this S-DI approach must be such that the relatively rich regions of local equivalence (<i>ϕ</i> &gt; 0.7) that reach higher combustion temperatures and generate NO_x and the overly lean regions (<i>ϕ</i> &lt; 0.3) that cause combustion inefficiency and instability are both minimized. This work investigates the implications of injector included angle and injection pressure at a low-load operating condition on the in-cylinder fuel stratification through the use of three-dimensional computational fluid dynamics (3D-CFD) simulations coupled with Large Eddy Simulation (LES) turbulence modeling. A computational model was developed and validated against experimental data collected at two low-load conditions on a medium-duty single cylinder LTGC engine at Sandia National Laboratories. Fuel stratification is analyzed using in-cylinder cut-planes based on local equivalence ratio as well as fuel mass-weighted joint probability density functions (jPDFs). Observed trends in combustion performance and emissions formation are presented in the context of the fuel stratification generated by increased injection pressure and a wider injector included angle.</div></div>