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During the 1980's, vegetable oils, microemulsions containing fatty alcohols as surfactants, and fatty esters have been extensively investigaed as alternative fuels to #2 diesel fuel (DF-2) used in farm tractors. Despite the importance of vegetable oils (mainly triglycerides) and fatty derivatives to the alternative fuel program, cetane numbers for pure triglycerides and many fatty derivatives were not reported. In the current study, estimated cetane numbers of these materials have been determined by use of a constant volume combustion bomb. Prior research has shown that this equipment can produce cetane numbers that correlate satisfactorily with engine cetane numbers as determied by ASTM D 613. The influence of chemical structure on ignition delay and cetane number was investigated. Evidence is presented that shows the current cetane number scale is not always suitable for these fatty materials. Suggestions are made as to what might be done to remedy this problem.

Substantial efforts have been made to reduce emissions from future heavy-duty diesel engines by control of selected fuel properties. U.S. diesel fuel for transportation use is scheduled by EPA to have low sulfur (≤ 0.05 wt. %) and a minimum cetane index of 40 by 1994 to reduce emissions. In addition, California has mandated that low sulfur diesel fuels contain less than 10 volume percent aromatics by 1994. Relative to emissions impact, diesel engine design and state-of-tune are perhaps even more important than proposed changes to diesel fuel. The work reported here examined emissions from a 1986 DDC 6V92-TA bus engine using fuels with variation in cetane number, aromatic level, 90 percent boiling point, and sulfur content. The engine was run on these fuels with selected maladjustments to examine their interactive effects on bus engine emissions. Except for HC emissions, regulated emissions were affected more by state-of-tune than by variation in test fuel properties.

Four military engines were tested to determine the effect of fuel properties on engine performance. These engines were the Detroit Diesel (DD) 4-53T, Continental Motors LDT-465-1C, Cummins NTC-350, and the Caterpillar 3208T. For this program, 18 fuels were blended to attain wide variations in kinematic viscosity, cetane number, ten-percent boiling point (10%BP), and aromatic content. Each of the eighteen fuels was run at the same relative speed and energy levels in each engine. Loads attained from the given speed-energy points were analyzed using the computer program SAS. These multiple linear regression analyses yielded a stable load prediction equation for each engine with energy, speed, aromatic content, inlet air temperature, kinematic viscosity, and 10%BP as the independent variables. Two additional fuel blends were run as cross-validations. Predicted loads agreed well with observed loads for these fuels except at low speed-energy points in some engines.

Three crude shale oils were chosen from six candidates to investigate their possible use as substitutes for No. 2 diesel fuel. Satisfactory hot engine operation was achieved on the crudes using a fuel heating system, allowing emissions characterization during transient and steady-state operation. Regulated gaseous emissions changed little with the crudes compared to diesel fuel; but total particulate and soluble organics increased, and larger injector tip deposits and piston crown erosion were observed. After engine rebuild, two minimally-processed shale oils were run without the fuel heating system, causing no engine problems. Most emissions were higher than for No. 2 fuel using an SO percent distillate of crude shale oil, but lower using a hydrotreated form of the distillate.

A loop-scavenged, two-stroke, spark-assisted DI diesel engine was developed by modifying an outboard marine gasoline engine to operate on diesel fuel with high fuel efficiency similar to a diesel engine, yet retain the two-stroke engine advantages of low cost, light weight, and high power-to-weight ratio. Engine modification was concentrated in the area of the combustion system, including transfer port design to generate air swirl in the cylinder, and combustion chamber design to generate air squish and turbulence. Bore and stroke (84 × 72 mm) remained the same as those of the base engine. The experimental engine used the production engine's piston, crankshaft, connecting rod, bearings, and cylinder block. The transfer port design was optimized using a flow test bench for best swirl and air flow pattern with a simple flow visualization technique. The best combustion chamber geometry, compression ratio, and fuel injection spray pattern were determined through engine experiments.

Four major coal fuel projects which were performed at Southwest Research Institute over the past ten years are reviewed. Beginning with the “Alternative Fuels for Highway Utilization” project in 1979, and the success of carbon-black/diesel fuel slurries, the development of the coal slurries is traced to the current technology. Most recently, full-scale locomotive engines have been operated on 50% coal in water slurries at thermal efficiencies approaching that of diesel fuel performance. The paper is concluded with a recommended engine design for coal slurries.

Increasingly stringent emission requirements for heavy-duty diesel engines stresses the importance of both engine design and diesel fuel quality. The Coordinating Research Council sponsored this test work to yield quantitative emission data and emission models to relate diesel fuel properties to emissions from modern heavy-duty diesel engines. Regulated and selected unregulated emissions from three engines were measured over the EPA transient test procedure using several fuels having controlled variation in three primary fuel properties: aromatics, volatility (as the 90 percent boiling point temperature), and sulfur. Models for transient composite emissions were obtained using multiple linear regression techniques, and changes to regulated emissions for selected changes in fuel properties were estimated from the models. Of the three primary fuel variables, aromatic content and volatility were significant for emissions of HC, CO, and NOx.

A variable-compression ratio, direct-injection diesel engine (VCR) has been designed and assembled at Southwest Research Institute with the intention of examining the current procedures for rating the ignition quality of diesel fuels and the meaning of ignition delay as an indicator of ignition and combustion quality. Using a slightly modified ASTM D 613 procedure, the engine has been used to rate the ignition quality of 43 different test fuels. The ratings obtained in the VCR engine are compared to the corresponding rating obtained using the standard cetane rating procedure. Some of the problems associated with the standard procedure became apparent during these experiments. The experimental results are discussed in terms of the problems and the advantages of a proposed VCR-based rating procedure.