Implementation of a Dual Coil Ignition Strategy in a Split-Cycle Engine 2019-01-0726

A Split-Cycle engine fueled with methane has been constructed and operated at the University of Windsor. A split-cycle engine consists of two interconnected cylinders working together to preform the four engine strokes. Cylinder 1 preforms intake and compression strokes while cylinder 2 is where combustion, expansion and exhaust occur. The connecting high pressure crossover passage is where methane is injected, resulting in a well pre-mixed air-fuel mixture. Transfer occurs to the combustion cylinder near TDC, resulting in intense small scale turbulence that leads to short combustion durations under 30° CA. Short durations are achieved despite low engine speeds of 850-1200 rpm, late combustion phasing and part loads. Of note is the lean limit of operation of the engine at the equivalence ratio Φ = 0.85, which is high compared to other natural gas engines which have limits around Φ = 0.6. The high levels of turbulence combined with a high amount of residual mass being trapped in the combustion cylinder are considered to be the limiting factor for the lean limit of operation.

An extension of the lean limit is explored using a dual coil ignition strategy in which two coils are discharged through a single spark plug, increasing the amount of energy deposited to each kernel. Similar strategies have shown the effectiveness of increased energy in both highly turbulent and diluted mixtures. The normalized pressure ratio (PR_N) method is used to acquire results for combustion phasing and cyclic variability. The dual coil strategy has been shown to be an effective way to extend the lean limit of operation of an engine in lean, dilute and turbulent conditions. The COV_IMEP, COV_LPP and number of misfires decrease, indicating increased combustion stability. Equivalence ratio is extended to Φ = 0.81. It can be used in scenarios where combustion in the lean condition is desired.