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This paper investigates Homogeneous Charge Compression Ignition (HCCI) combustion on an engine that is fuelled with ethanol, iso-octane, and ethanol/iso-octane. The engine is a four-stroke three cylinder indirect injection type diesel engine converted to a single cylinder HCCI operation. In order to clarify the effects of fuel chemistry on HCCI combustion, the trials were done at a constant engine speed, a fixed initial charge temperature and engine coolant temperature. The HCCI engine was fuelled with a lean mixture of air and fuel (ethanol, iso-octane or mixture of ethanol/iso-octane). The engine performance parameters studied here include indicated mean effective pressure (IMEP) and thermal efficiency. Heat-release rate (HRR) analysis was done to determine the effect of fuels on combustion on-set. The experimental results demonstrate that the addition of iso-octane to ethanol retards the on-set of combustion and subsequently leads to a reduction of the IMEP and thermal efficiency.

This paper investigates the expansion of the HCCI operating range and combustion control by use of internal fuel reforming with subsequent reduction of NO emissions through Exhaust Gas Recirculation (EGR). The study is focused on multi-step simulation of the engine cycle, comprised of a fuel reformation cycle and a HCCI combustion cycle, with and without EGR. The study is carried out using a single-zone well-stirred reactor model and established reaction mechanisms. The HCCI engine cycle is fueled with a lean mixture of air and ethanol. This study demonstrates that supplementing EGR with internal reforming reduces the NO emissions level. Furthermore, the study shows that internal fuel reforming extends the operational range of HCCI engines into the partial load region and is effective in the combustion onset control. However, the model requires several enhancements in order to moderate the cycle pressure rise and pressure magnitude, and to lower the cycle temperatures and NO emissions.

The effects of the addition of small amounts of molecular and atomic hydrogen/oxygen on laminar burning velocity, pollutant concentrations, and adiabatic flame temperatures of premixed, laminar, freely propagating iso-octane flames are investigated using CHEMKIN kinetic simulation package and a chemical kinetic mechanism at different equivalence ratios. It is shown that hydrogen/oxygen additives increase the laminar burning velocities. Increased hydroxyl (OH) concentrations resulted in reduced carbon monoxide (CO) emissions in every stoichiometric ratios investigated. Additives also increased the adiabatic flame temperature of iso-octane/air combustion, thereby causing increased NOx concentrations for all additives at all stoichiometries.

This research involved studying the effects of adding small amounts of hydrogen or hydrogen and oxygen to a gasoline fuelled spark ignition (SI) engine at part load. The hydrogen and oxygen were added in a ratio of 2:1, mimicking the addition of water electrolysis products. It was found that the effects of hydrogen addition (≈ 2.8% of the fuel by mass, ≈ 60% by volume) decreased as the fuel/air equivalence ratio approached ϕ = 1. When operating at ϕ ≤ 0.8, the torque, indicated mean effective pressure (imep) and NO emissions increased and cycle-to-cycle variation decreased with hydrogen addition. The improvements in engine performance and increase in NO emissions were related to a faster burn rate shown by a decrease in burn duration with the addition of hydrogen. Further, the addition of hydrogen only and hydrogen and oxygen in a ratio of 2:1 were compared. The extra oxygen had little effect on engine performance other than an increase in NO exhaust concentration ∼ 500 ppm.