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This study investigated the RCCI (Reactivity Controlled Compression Ignition) of PFI (Port Fuel Injection) of n-butanol with direct injection (DI) of a high linoleic acid content biodiesel, cottonseed (CS100). The experimental omnivorous-fuel engine was operated at 1400 rpm and 6 bar indicated mean effective pressure (IMEP) with 20% cooled EGR. The mass ratio of n-butanol injected comprised of 50% of the total fuel mass. The dual fueling strategy of RCCI changed the conventional diesel combustion (CDC) apparent heat release profile. With the new fueling strategy the heat release was split into two regions of high temperature heat release when using CS100. The first occurred before top dead center (BTDC) from the high reactivity fuel and the second peak occurred due to the combustion of the low reactivity fuel (n-butanol) after top dead center (ATDC). ULSD did not produce this same split in heat release due to the longer ignition delay. The ignition delay for CS100 was shortened by 0.15 ms when compared to ULSD because of the high palmitic acid content in the biodiesel. The RCCI process itself extended the ignition delay about 0.17 ms (about 1.4 CAD) suggesting the possibility of controlling combustion phasing for both RCCI fueling strategies of ULSD and CS100. The CA50 occurred similarly at 10° ATDC for ULSD and CS100 however, RCCI shifted the CA50’s (7° and 8° ATDC for CS100 and ULSD respectively). Soot emissions exhibited a decrease with the PFI of n-butanol because of the highly oxygenated nature of the fuel by 80%. In summary, RCCI stratification using n-Butanol as the low reactivity fuel significantly reduced soot emissions when using either a high linoleic acid content biofuel or ULSD while also suggesting control over combustion phasing.

In this study, the combustion and emissions characteristics of Reactivity Controlled Compression Ignition (RCCI) obtained by direct injection (DI) of S8 and port fuel injection (PFI) of n-butanol were compared with RCCI of ultra-low sulfur diesel #2 (ULSD#2) and PFI of n-butanol at 6 bar indicated mean effective pressure (IMEP) and 1500 rpm. S8 is a synthetic paraffinic kerosene (C6–C18) developed by Syntroleum and is derived from natural gas. S8 is a Fischer-Tropsch fuel that contains a low aromatic percentage (0.5 vol. %) and has a cetane number of 63 versus 47 of ULSD#2. Baselines of DI conventional diesel combustion (CDC), with 100% ULSD#2 and also DI of S8 were conducted. For both RCCI cases, the mass ratio of DI to PFI was set at 1:1. The ignition delay for the ULSD#2 baseline was found to be 10.9 CAD (1.21 ms) and for S8 was shorter at 10.1 CAD (1.12 ms). In RCCI, the premixed charge combustion has been split into two regions of high temperature heat release, an early one BTDC from ignition of ULSD#2 or S8, and a second stage, ATDC from n-butanol combustion. RCCI with n-butanol increased the NOx because the n-butanol contains 21% oxygen, while S8 alone produced 30% less NOx emissions when compared to the ULSD#2 baseline. The RCCI reduced soot by 80–90% (more efficient for S8). However, S8 alone showed a considerable increase in soot emissions compared with ULSD#2. The indicated thermal efficiency was the highest for the ULSD#2 and S8 baseline at 44%. The RCCI strategies showed a decrease in indicated thermal efficiency at 40% ULSD#2-RCCI and 42% and for S8-RCCI, respectively. S8 as a single fuel proved to be a very capable alternative to ULSD#2 in terms of combustion performance nevertheless, exhibited higher soot emissions that have been mitigated with the RCCI strategy without penalty in engine performance.

This study compares combustion of Jet-A in an indirect injection (IDI) compression ignition engine and a direct injection (DI) compression ignition engine at the same load and speed. The Jet-A was blended (75Jet-A): 75% Jet-A and 25% Ultra Low Sulfur Diesel # 2 (ULSD) by mass. Both engines had a load of 4.5 bars Indicated Mean Effective Pressure (IMEP) and were run at 2000 RPM. The IDI engine configuration was very similar to that used in High Mobility Multipurpose Wheeled Vehicles (HMMWV). The research showed that combustion pressure in the IDI engine separate combustion chamber was 81 bars versus 71 bars in the main combustion chamber showing high gas-dynamics losses at transfer passages while in the DI engine the peak pressure reached 65 bars. The Apparent Heat Release Rate (AHRR) in the IDI engine has both the premixed and diffusion stage combined while in the DI classical combustion there are visible both the premixed and diffusion burn stages. The results show that in both engines there is a Low Temperature Heat Release (LTHR) region before top dead center (BTDC). The mass averaged instantaneous temperature reached 1750 K in the direct injection engine being the same for both fuels and for the IDI engines reached 1700 K in main combustion chamber and 1950 K in the separate combustion chamber for both fuels. The study showed that there are significant differences in the shape of the AHRR between the engines, nevertheless, the Jet-A has very similar combustion characteristics with ULSD in both combustion systems making a viable option as a substitute fuel to use in High Mobility Multipurpose Wheeled Vehicles (HMMWV).

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