The heat release analysis of bio-butanol/gasoline blends on a high speed SI (spark ignition) engine

• The impacts of ignition timing, butanol blend ratio, engine load, and fuel–air composition on heat release were studied.
• Butanol provides higher knock resistance, allowing more advanced spark timing.
• Engine load has stronger impact on combustion process than speed or fuel type.
• Fuel–air ratio is the dominated factor rather than fuel type in fuel oxidation rate.

In this study, experiments were conducted on a single-cylinder high speed SI (spark ignition) engine fueled with 30 and 35%vol butanol/gasoline blends and compared to the pure gasoline. This research is trying to find out the common principles about the influence on combustion heat release of SI engine for variables such as ignition timing, engine load, and butanol blend ratio in a wide engine speed range (3000–8500 rpm). The results showed that butanol provides higher knocking resistance by allowing advance the ignition timing in SI engines, leading to more efficient combustion. The laminar burning velocity of butanol is higher than that of gasoline, but that doesn't guarantee a faster burning speed in a real engine unless the combustion process is more reasonably organized, such as using the optimum ignition timing. In the overall trend, as the butanol blend ratio increasing, one can achieve a more efficient combustion process with using the optimum operating parameters. Obviously, the rate of heat release became slower and declined in peak value as the engine load decreases, accompanied by a shift of peak value to later for both pure gasoline and butanol/gasoline blends. In the aspect of fuel oxidation rate, the fuel–air ratio is the dominated factor rather than fuel type.