Spray–Wall Interactions in a Small-Bore, Multicylinder Engine Operating With Reactivity-Controlled Compression Ignition

Abstract

Experimental work on reactivity-controlled compression ignition (RCCI) in a small-bore, multicylinder engine operating on premixed iso-octane, and direct-injected n-heptane has shown an unexpected combustion phasing advance at early injection timings, which has not been observed in large-bore engines operating under RCCI at similar conditions. In this work, computational fluid dynamics (CFD) simulations were performed to investigate whether spray–wall interactions could be responsible for this result. Comparison of the spray penetration, fuel film mass, and in-cylinder visualization of the spray from the CFD results to the experimentally measured combustion phasing and emissions provided compelling evidence of strong fuel impingement at injection timings earlier than −90 crank angle degrees (deg CA) after top dead center (aTDC), and transition from partial to full impingement between −65 and −90 deg CA aTDC. Based on this evidence, explanations for the combustion phasing advance at early injection timings are proposed along with potential verification experiments.