Working fluid composition effects on methane oxycombustion in an SI-engine: EGR vs. CO₂

Reducing greenhouse-gas production through carbon capture is a key strategy in addressing global climate change. Oxycombustion using carbon dioxide, water, or a combination of the two as the diluent when burning hydrocarbon fuels with pure oxygen is an approach that allows for easy post-combustion carbon capture. In this work, oxycombustion experiments in a spark ignited engine using methane were conducted using carbon dioxide or EGR (in which exhaust water is not condensed out) as the working fluid. Between the two cases, EGR produced higher brake efficiencies and a lower coefficient of variation of the indicated mean effective pressure for similar operating conditions. For both working fluids it was necessary to have the oxygen concentration higher than 21%. Numerical modeling, using several mechanisms for comparison, indicates that the computed laminar flame speed with EGR is more than twice that using only carbon dioxide. However, for both EGR and carbon dioxide, laminar flame speeds were reduced significantly relative to methane-in-air combustion. Numerical modeling of the methane and oxygen with EGR working fluid provided good agreement with engine results. Based on this work, the use of oxycombustion in engines and other devices should consider including water in the working fluid to improve flame speed and combustion performance.