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Controlling n-Heptane HCCI
Combustion With Partial
Reforming: Experimental Results and Modeling Analysis
Vahid Hosseini
W. Stuart Neill
Institute for Chemical Process and
Environmental Technology,
National Research Council,
Ottawa, ON, K1A 0R6, Canada

M. David Checkel
University of Alberta,
Edmonton, AB, T6G 2G8, Canada

1

One potential method for controlling the combustion phasing of a homogeneous charge compression ignition (HCCI) engine is to vary the fuel chemistry using two fuels with different auto-ignition characteristics. Although a dual-fuel engine concept is technically feasible with current engine management and fuel delivery system technologies, this is not generally seen as a practical solution due to the necessity of supplying and storing two fuels. Onboard partial reforming of a hydrocarbon fuel is seen to be a more attractive way of realizing a dual-fuel concept, while relying on only one fuel supply infrastructure. Reformer gas (RG) is a mixture of light gases dominated by hydrogen and carbon monoxide that can be produced from any hydrocarbon fuel using an onboard fuel processor. RG has a high resistance to auto-ignition and wide flammability limits. The ratio of H2 to CO produced depends on the reforming method and conditions, as well as the hydrocarbon fuel. In this study, a cooperative fuel research engine was operated in
HCCI mode at elevated intake air temperatures and pressures. n-heptane was used as the hydrocarbon blending component because of its high cetane number and well-known fuel chemistry. RG was used as the low cetane blending component to retard the combustion phasing. Other influential parameters, such as air/fuel ratio, EGR, and intake temperature, were maintained constant. The experimental results show that increasing the RG fraction retards the combustion phasing to a more optimized value causing indicated power and fuel conversion efficiency to increase. RG reduced the first stage of heat

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