Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Gregory J Thompson

Committee Co-Chair

William J Cannella

Committee Member

Nigel N Clark

Committee Member

Mridul Gautam

Committee Member

Hailin Li

Committee Member

John P Nuszkowski

Abstract

Reactivity controlled compression ignition (RCCI) is a form of dual-fuel combustion that exploits the reactivity difference between two fuels to control combustion phasing. This combustion approach limits the formation of oxides of nitrogen (NOX) and soot while retaining high thermal efficiencies associated with compression-ignition (CI) engines. Theoretical and applied research has been conducted by researchers at several other institutions detailing RCCI combustion characteristics, exhaust emissions, fuel efficiency, and operability. However, the discussion of fuel property effects on RCCI combustion has been limited. Previous research on fuel properties that influence RCCI combustion have predominantly focused on the low reactivity fuel. The research presented herein was performed to determine the influences that high reactivity fuel properties have on RCCI combustion characteristics, exhaust emissions, fuel efficiency, and the operable load range.;A General Motors 4-cylinder, 1.9 liter, light-duty CI engine was converted to run on diesel fuel (high reactivity fuel) and compressed natural gas (CNG) (low reactivity fuel). The engine was operated at 2100 revolutions per minute (RPM), which is near its intermediate speed and where previous low temperature combustion (LTC) research has been performed. Two different loads were imposed on the engine, 3.6 bar brake mean effective pressure (BMEP) and 6 bar BMEP. A preliminary parametric study was conducted at each load to determine which engine control parameters had the largest effect on RCCI combustion, exhaust emissions, and fuel efficiency. From this study, a test matrix was developed that varied intake manifold air pressure (IMAP) and the location of 50 percent mass fraction burned (CA50) for the 3.6 bar BMEP load condition. At the 6 bar BMEP load condition a test matrix that varied the direct injection (DI) start of injection (SOI) timing and CA50 was developed. CA50 was controlled by adjusting the ratio of CNG to diesel (percentage CNG). The engine was operated at each point of these test matrices with nine different diesel fuels that had varying fuel properties, including cetane number (CN), aromatic content (AC), and distillation temperatures. The results from these tests were used to identify high reactivity fuel property effects on RCCI combustion characteristics, exhaust emissions, fuel efficiency, and the operable load range.;Results from the experiment demonstrated that CN of the diesel fuel had a dominant effect on nearly all facets of RCCI combustion, exhaust emissions, and fuel efficiency. RCCI operation with diesel fuels whose CN was lower than 33 resulted in substantially higher NOX emissions and in-cylinder pressure rise rates (PRRs) that limited the operable load range, compared to fuels with a CN ranging from 44 to 54. High CN diesel fuels with a low AC (<23%) required the largest percentage CNG to maintain combustion phasing, 70.5% to 78.6% of total fuel energy input as CNG at 3.6 bar BMEP and 73.4% to 83.0% at 6 bar BMEP. High CN, low AC diesel fuels also operated at the highest fuel conversion efficiency, 27.3% to 30.2% at 3.6 bar BMEP and 38.0% to 39.4% at 6 bar BMEP. Furthermore, in-cylinder PRR decreased as CN of the diesel fuel increased which would allow for higher engine loads to be achieved.

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