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The alternative fuel jet propellant 8 (JP-8, NATO F-34) can be used as an auto-ignition source instead of diesel. Because it has a higher volatility than diesel, it provides a better air-fuel premixing condition than a conventional diesel engine, which can be attributed to a reduction in particulate matter (PM). In homogeneous charged compression ignition (HCCI) or dual-fuel premixed charge compression ignition (PCCI) combustion or reactivity controlled compression ignition (RCCI), nitrogen oxides (NOx) can also be reduced by supplying external exhaust gas recirculation (EGR). In this research, the diesel and JP-8 injection strategies under conventional condition and dual-fuel PCCI combustion with and without external EGR was conducted. Two tests of dual-fuel (JP-8 and propane) PCCI were conducted at a low engine speed and load (1,500 rpm/IMEP 0.55 MPa). The first test was performed by advancing the main injection timing from BTDC 5 to 35 CA to obtain the emissions characteristics.

In this work, the operating strategy for diesel injection methods and a way to control the exhaust gas recirculation (EGR) rate under dual-fuel PCCI combustion with an appropriate ratio of low-reactivity fuel (propane) to achieve high combustion stability and low emissions is introduced. The standards of combustion stability were carbon monoxide (CO) emissions below 5,000 ppm and a CoV of the indicated mean effective pressure (IMEP) below 5 %. Additionally, the NOx emissions was controlled to not exceed 50 ppm, which is the standard of conventional diesel combustion, and PM emissions was kept below 0.2 FSN, which is a tenth of the conventional diesel value without a diesel particulate filter (DPF). The operating condition was a low speed and load condition (1,500 rpm/ near gIMEP of 0.55 MPa).

Direct-injection spark-ignition (DISI) engines are regarded as a promising technology for the reduction of fuel consumption and improvement of engine thermal efficiency. However, due to direct injection, the shortened fuel-air mixing duration leads to a spatial gradient of the equivalence ratio, and these locally rich regions cause the formation of particulate matter. In the current study, numerical investigations on pollutant formation in a DISI engine were performed using combined flamelet models for premixed and diffusion flames. The G-equation model for partially premixed combustion was improved by incorporating the laminar flamelet library. Gasoline fuel was represented as a ternary mixture of gasoline surrogate and its laminar flame speeds were obtained under a wide range of engine operating conditions.

Novel Diesel combustion concepts such as premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) promise lower NOx and PM emissions than those of conventional Diesel combustion. RCCI, which can be implemented using low-reactivity fuels such as gasoline or gases and high-reactivity fuels such as Diesel, has the potential to achieve extremely low emissions and improved thermal efficiency. However, to achieve RCCI combustion, a higher boost pressure than that of a conventional engine is required because a high EGR rate and a lean mixture are necessary to achieve a low combustion temperature. However, higher boost pressures can cause damage to intake systems. In this research, the addition of gaseous fuel to a CI engine is investigated to reduce engine emissions, mainly NOx and PM emissions, with the same IMEP level. Two different methods were evaluated.