High Efficiency, Low Emissions RCCI Combustion by Use of a Fuel Additive

Heavy-duty engine experiments were conducted to explore reactivity controlled compression ignition (RCCI) combustion through addition of the cetane improver di-tert-butyl peroxide (DTBP) to pump gasoline. Unlike previous diesel/gasoline dual-fuel operation of RCCI combustion, the present study investigates the feasibility of using a single fuel stock (gasoline) as the basis for both high reactivity and low reactivity fuels. The strategy consisted of port fuel injection of gasoline and direct injection of the same gasoline doped with a small volume percent addition of DTBP. With 1.75% DTBP by volume added to only the direct-injected fuel (which accounts for approximately 0.2% of the total fueling) it was found that the additized gasoline behaved similarly to diesel fuel, allowing for efficient RCCI combustion. The single fuel results with DTBP were compared to previous high-thermal efficiency, low-emissions results with port injection of gasoline and direct injections of diesel. The comparison between fueling strategies found that the higher volatility of gasoline enabled a reduction in the direct injection pressure from 800 (bar) with diesel to 400 (bar) with gasoline. At the tested conditions, the peak gross indicated based thermal efficiency was over 57%. The emissions trends and magnitudes of the single fuel strategy were also comparable to those of the diesel/gasoline dual-fuel strategy, and both engine-out NO_X and PM met EPA HD 2010 emissions mandates without aftertreatment. Also, the decreased low temperature heat release with the single fuel strategy was found to lower compression work and increased thermal efficiency by approximately 1% over the diesel/gasoline case. The results demonstrate that a very small percentage of an appropriate additive can be used to establish a sufficiency large reactivity gradient to match the performance of a dual fuel strategy when operated in the RCCI combustion regime.