Optimization of soy-biodiesel combustion in a modern diesel engine

Michael P Bunce, Purdue University

Abstract

As global petroleum demand continues to increase, alternative fuel vehicles are becoming the focus of increasing attention. Biodiesel has emerged as an attractive alternative fuel option due to its domestic availability from renewable sources, its relative physical and chemical similarities to conventional diesel fuel, and its miscibility with conventional diesel. Biodiesel combustion in modern diesel engines does, however, generally result in higher fuel consumption and higher nitrogen oxide (NOx) emissions compared to diesel combustion due to fuel property differences including calorific value and oxygen content. The purpose of this study is to determine the optimal engine decision-making for 100% soy-based biodiesel and blends of 20% and 5% biodiesel to accommodate fuel property differences via modulation of air-fuel ratio (AFR), exhaust gas recirculation (EGR) fraction, fuel rail pressure, and start of main fuel injection pulse (SOI) at over 150 different random combinations, each at 4 very different operating locations. B100 combustion with stock engine control module (ECM) decision-making resulted in increases in NOx at all 4 locations (9% to 39%) and fuel consumption (13% to 27%) over the nominal diesel levels accompanied by substantial reductions in particulate matter (over 75%). B20 and B5 combustion at the nominal diesel settings exhibited NOx increases (8% to 34%) at the 3 NTE region operating locations, while brake specific NOx (BSNOx) decreased slightly at the non-NTE region location. These were again accompanied by increases in fuel consumption (3% to 8%) and substantial particulate matter reductions. The biodiesel optimal settings were defined as the parameter settings that produced comparable or lower NOx, particulate matter (PM), and peak rate of change of in-cylinder pressure (peak dP/dt, a metric for noise) with respect to nominal diesel levels, while minimizing brake specific fuel consumption (BSFC). At most of the operating locations across fuel blends, the optimal engine decision-making was clearly shifted to lower AFRs and higher EGR fractions in order to reduce the observed increases in NOx at the nominal settings, and to more advanced timings in order to mitigate the observed increases in fuel consumption at the nominal settings. These optimal parameter combinations for B5, B20, and B100 were able to reduce NOx and noise levels below nominal diesel levels while largely maintaining the substantial PM reductions. However, the optimal settings were only able to reduce BSFC to levels comparable to or below B0 nominal levels at only 1 operating location with B5 fuel. In sum, these optimal parameter combinations had little or no net impact on reducing the biodiesel fuel consumption penalty.

Degree

M.S.M.E.

Advisors

Shaver, Purdue University.

Subject Area

Alternative Energy|Automotive engineering|Mechanical engineering

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