Michael Bunce

Optimization of soy-biodiesel combustion in a modern diesel engine

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 nitrogen oxide (NO x ) 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 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 at over 150 different random combinations, each at four very different operating locations. Applying the nominal diesel settings to biodiesel combustion resulted in increases in NO x at three of the four locations (up to 44%) and fuel consumption (11–20%) over the nominal diesel levels accompanied by substantial reductions in particulate matter (over 80%). The biodiesel optimal settings were defined as the parameter settings that produced comparable or lower NO x , particulate matter (PM), and peak rate of change of in-cylinder pressure (peak d P /d t , a metric for noise) with respect to nominal diesel levels, while minimizing brake specific fuel consumption (BSFC). At most of the operating locations, the optimal engine decision-making was clearly shifted to lower AFRs and higher EGR fractions in order to reduce the observed increases in NO x 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 biodiesel were able to reduce NO x and noise levels below nominal diesel levels while largely maintaining the substantial PM reductions. These parameter combinations, however, had little (maximum 4% reduction) or no net impact on reducing the biodiesel fuel consumption penalty.

Steady-State Biodiesel Blend Estimation via a Wideband Oxygen Sensor

A substantial opportunity exists to reduce carbon dioxide (CO 2 ) emissions, as well as dependence on foreign oil, by developing strategies to cleanly and efficiently use biodiesel, a renewable domestically available alternative diesel fuel. However, biodiesel utilization presents several challenges, including decreased fuel energy density and increased emissions of smog-generating nitrogen oxides (NO x ). These negative aspects can likely be mitigated via closed-loop combustion control provided the properties of the fuel blend can be estimated accurately on-vehicle, in real-time. To this end, this paper presents a method to practically estimate the biodiesel content offuel being used in a diesel engine during steady-state operation. The simple generalizable physically motivated estimation strategy presented utilizes information from a wideband oxygen sensor in the engines exhaust stream, coupled with knowledge of the air-fuel ratio, to estimate the biodiesel content of the fuel. Experimental validation was performed on a 2007 Cummins 6.7 l ISB series engine. Four fuel blends (0%, 20%, 50%, and 100% biodiesel) were tested at a wide variety of torque-speed conditions. The estimation strategy correctly estimated the biodiesel content of the four fuel blends to within 4.2% of the true biodiesel content. Blends of 0%, 20%, 50%, and 100% were estimated to be 2.5%, 17.1%, 54.2%, and 96.8%, respectively. The results indicate that the estimation strategy presented is capable of accurately estimating the biodiesel content in a diesel engine during steady-state engine operation. This method offers a practical alternative to in-the-fuel type sensors because wideband oxygen sensors are already in widespread production and are in place on some modern diesel vehicles today.

FUNGIBLE AND COMPATIBLE BIOFUELS: LITERATURE SEARCH, SUMMARY, AND RECOMMENDATIONS

The purpose of the study described in this report is to summarize the various barriers to more widespread distribution of bio-fuels through our common carrier fuel distribution system, which includes pipelines, barges and rail, fuel tankage, and distribution terminals. Addressing these barriers is necessary to allow the more widespread utilization and distribution of bio-fuels, in support of a renewable fuels standard and possible future low-carbon fuel standards. These barriers can be classified into several categories, including operating practice, regulatory, technical, and acceptability barriers. Possible solutions to these issues are discussed; including compatibility evaluation, changes to bio-fuels, regulatory changes, and changes in the distribution system or distribution practices. No actual experimental research has been conducted in the writing of this report, but results are used to develop recommendations for future research and additional study as appropriate. This project addresses recognized barriers to the wider use of bio-fuels in the areas of development of codes and standards, industrial and consumer awareness, and materials compatibility issues.

Uncertainty Analysis of Wideband Oxygen Sensor Based Strategy for Steady-State Biodiesel Blend Estimation

Real-time estimation and accommodation is critical for clean and efficient utilization of biodiesel blends in “fuel flexible” diesel engines. This paper utilizes a generalizable, physically-based, and experimentally-verified blend estimation strategy which uses exhaust oxygen sensor measurements coupled with engine control module (ECM) estimates of fuel and air flow to estimate the biodiesel blend fraction. The paper assesses the impact of uncertain variables on the estimation strategy. The strategy is essentially unaffected by biodiesel feedstock variations and, when applied to a Cummins 6.7-liter engine, is not susceptible to significant blend estimation discrepancies in response to expected fuel flow and oxygen sensor errors. However, observed errors in air flow estimates are expected to lead to large blend estimate errors. Use of direct air flow measurement or the use of a dynamic estimator (e.g., Kalman filter) synthesized from the model, the subject matter of future work, is expected to significantly reduce these errors.Copyright

DOE Project 18545, AOP Task 2.0B, CRADA with Reaction Design

We ran 5 FACE fuels and 8 surrogate blends in diesel combustion with detailed particulate and exhaust chemistry measurements to provide data needed to develop and evaluate a kinetic model for particulate formation. Surrogate blends duplicated engine performance of real fuels. We demonstrated that a simple 2 surrogate blend is capable of duplicating the range of engine response for the FACE fuels, but that further tuning and complexity will be needed to reproduce emissions. We assisted in setting up a Jaguar computer user program for bench marking parallel solvers for chemistry in GPU machine environment. This program has just been approved by the Jaguar user facility and will begin in 2012.

Closed-Loop Control Framework for Fuel-Flexible Combustion of Biodiesel Blends

This paper presents a closed-loop control framework for fuel-flexible combustion control of biodiesel blends. This framework consists of two parts: blend detection and blend accommodation. Blend detection can be accomplished by an experimentally-validated dynamic estimator using exhaust oxygen and air-fuel ratio information. Blend accommodation can be accomplished by changing the control variables that the engine control module uses, namely, replacing exhaust gas recirculation fraction with combustible oxygen mass fraction, replacing total injected fuel mass with total injected fuel energy, and replacing start of main injection timing with end of main injection timing. With the conventional control structure it is experimentally shown that pure biodiesel (B100) produced 38% more brake specific nitrogen oxides (BSNOx) than pure conventional diesel (B0). With the new proposed structure, B100 produced not only lower BSNOx than B0, but also higher torque, higher brake thermal efficiency, lower particulate matter, and lower combustion noise than B0. Comparable experimental results are also presented for B5 and B20 blends.Copyright

Optimization of the Performance and Emissions of Soy Biodiesel Blends in a Modern Diesel Engine

As the world is faced with continued petroleum demand, the need for alternative fuels which are renewable and domestically available is becoming apparent. Biodiesel is one such attractive alternative fuel which has physical and chemical properties similar to, and miscible with conventional diesel. While biodiesel does have many advantages, due to fuel property differences including oxygenation and a lower calorific value than diesel fuel, biodiesel combustion often results in higher fuel consumption and higher nitrogen oxide (NOx ) emissions than diesel combustion. Stock diesel engine design and decision making target optimal performance with conventional diesel fuel, leading to suboptimal results for biodiesel. This study aimed to determine the appropriate engine decision making for the air/fuel ratio (AFR), exhaust gas recirculation (EGR) fraction, injection (rail) pressure, and start of main fuel injection (SOI) in a modern common rail diesel engine using variable geometry turbo-charging and operating with varying blend ratios of diesel and soy-based biodiesel fuel mixtures to minimize brake-specific fuel consumption (BSFC) and adhere to strict combustion noise, NOx and particulate matter (PM) emission constraints. When operating with the stock engine decision making, biodiesel blend combustion resulted in increases in NOx of up to 39% and fuel consumption increases up to 20% higher than the nominal diesel levels but also had substantial reductions in PM. Through modulation of the AFR, EGR fracton, rail pressure, and SOI at several operating points, it was demonstrated that the optimal engine decision-making for biodiesel shifted to lower AFRs and higher EGR fractions in order to reduce NOx , and shifted to more advanced timings in order to mitigate the observed increases in fuel consumption at the nominal settings. The optimal parameter combinations for B5 (5% biodiesel and 95% diesel), B20 (20% biodiesel and 80% diesel) and B100 (100% biodiesel) still maintained substantial PM reductions but resulted in NOx and noise levels below nominal diesel levels. However, these parameter combinations had little impact on reducing the biodiesel fuel consumption penalty but did improve the thermal efficiency of biodiesel blend combustion.Copyright

An Experimental and Simulation Study of Increases in Fuel Consumption and NOX Emissions in a Biofueled Diesel Engine

Alternative fuel vehicles are gaining importance as a means of reducing petroleum dependence. One attractive option is biodiesel, a renewable diesel fuel produced from plant or animal fats, since it significantly reduces carbon monoxide, unburned hydrocarbon, and particulate matter emissions as well as carbon dioxide when considered on a full life cycle basis. However, biodiesel combustion also typically results in increased fuel consumption and nitrogen oxide (NOx ) emissions relative to petroleum diesel. In order to determine the cause of and develop mitigation strategies for increased biodiesel fuel consumption and NOx emissions, an accurate simulation model was developed and validated. Key fuel properties as well as ignition delay characteristics were implemented in a previously validated whole engine model to reflect soy-biodiesel fuel. The model predictions were within 5% of experimental results for most values at the three operating points. Using this biodiesel model, the “biodiesel NOx effect” was linked to the near stoichiometric equivalence ratios for biodiesel.Copyright