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Adding oxygenates to diesel fuel has shown the potential for reducing particulate (PM) emissions in the exhaust. The objective of this study was to select the most promising oxygenate compounds as blending components in diesel fuel for advanced engine testing. A fuel matrix was designed to consider the effect of molecular structure and boiling point on the ability of oxygenates to reduce engine-out exhaust emissions from a modern diesel engine. Nine test fuels including a low-sulfur (∼1 ppm), low-aromatic hydrocracked base fuel and 8 oxygenate-base fuel blends were utilized. All oxygenated fuels were formulated to contain 7% wt. of oxygen. A DaimlerChrysler OM611 CIDI engine for light-duty vehicles was controlled with a SwRI Rapid Prototyping Electronic Control System. The base fuel was evaluated in four speed-load modes and oxygenated blends only in one mode. Each operating mode and fuel combination was run in triplicate.

The overall program objectives were three fold: assess the benefits and limitations of oxygenated diesel fuels on engine performance and emissions identify oxygenates most suitable for potential use in future diesel formulations based on physico-chemical properties (e.g. flash point), toxicity, biodegradability and estimated cost of production perform limited emissions and performance testing of the oxygenated diesel blends select at least two oxygenated compounds for advanced engine testing In Part 1 of this program which is described in this paper, an extensive literature review was conducted to identify potential oxygenates for blending into diesel fuels. As many as 71 oxygenates were identified for the initial screening process. Based on a set of physical and chemical properties, a screening methodology was developed to select the 8 oxygenates that will be eligible for engine testing.

“Gas-to-liquids” catalytic conversion technologies show promise for liberating stranded natural gas reserves and for achieving energy diversity worldwide. Some gas-to-liquids products are used as transportation fuels and as blendstocks for upgrading crude-derived fuels. Methylal (CH3-O-CH2-O-CH3), also known as dimethoxymethane or DMM, is a gas-to-liquid chemical that has been evaluated for use as a diesel fuel component. Methylal contains 42% oxygen by weight and is soluble in diesel fuel. The physical and chemical properties of neat methylal and for blends of methylal in conventional diesel fuel are presented. Methylal was found to be more volatile than diesel fuel, and special precautions for distribution and fuel tank storage are discussed. Steady state engine tests were also performed using an unmodified Cummins B5.9 turbocharged diesel engine to examine the effect of methylal blend concentration on performance and emissions.

A zero-dimensional cycle simulation model coupled with a chemical equilibrium model and a two-zone combustion model has been extended to predict nitric oxide formation and emissions from spark-ignited, lean-burn natural gas engines. It is demonstrated that using the extended Zeldovich mechanism alone, the NOx emissions from an 8.1-liter, 6-cylinder, natural gas engine were significantly under predicted. However, by combining the predicted NOx formation from both the extended Zeldovich thermal NO and the Fenimore prompt NO mechanisms, the NOx emissions were predicted with fair accuracy over a range of engine powers and lean-burn equivalence ratios. The effect of injection timing on NOx emissions was under predicted. Humidity effects on NOx formation were slightly under predicted in another engine, a 6.8-liter, 6-cylinder, natural gas engine. Engine power was well predicted in both engines, which is a prerequisite to accurate NOx predictions.

Recent studies suggest that the use of ethers as fuels or fuel additives may be a key to the simultaneous reduction of both particulate and NOx emissions from Diesel engines. The present study is directed towards understanding the chemical kinetics of autoignition of ethers under Diesel-like conditions. Autoignition experiments were performed in a constant volume apparatus (CVA), that allowed independent control of temperature, pressure, and oxidizing gas composition. Hollow cone sprays of methanol, dimethyl ether (DME), CH3OCH3, and dimethoxy methane (DMM), CH3OCH2OCH3, were created in quiescent air with a standard Diesel injector, and autoignition delays were inferred from pressure-time histories. A detailed chemical kinetic mechanism was developed to describe the pyrolysis, oxidation, and autoignition of methanol, DME and DMM at high pressures. The mechanism predicts autoignition delay time under Diesel-like conditions.

Catastrophic failures of fuel pumps used to transport ethanol have occurred in various facilities. Failures occurred in as little as 50 hours on pumps with a 2000 hour life expectancy. Post-failure inspection of the pumps showed corrosive pitting of the metal in the areas of sliding contact. Several potential causes, including cavitation, thermal expansion of pump parts, and fuel contaminants such as acetic acid were ruled out. Fuel samples from facilities with high pump failure rates passed all D 4806 specification tests for fuel-grade ethanol, including titratable acid by D 1613. However, pH readings as low as 2.0 indicated potentially corrosive fuels. Controlled tests on pumps and corrosion tests showed that pump failures correlated with fuel pH. Corrosive fuels were found to contain ethyl sulfate, which correlated with fuel pH. It appears that ethyl sulfate originates from sulfur dioxide, which is used as an antioxidant and antiseptic in the production of ethanol.

A menu-driven, PC-based model, ALAMO_ENGINE, has been developed to predict the nitrogen oxides (NOx) reductions in direct-injected, diesel engines due to exhaust gas recirculation (EGR), emulsified fuels, manifold or in-cylinder water injection, fuel injection timing changes, humidity effects, and intake air temperature changes. The approach was to use a diesel engine cycle simulation with detailed gas composition calculations for the intake and exhaust gases (including EGR, water concentration, fuel-type effects, etc.), coupled with a code to calculate stoichiometric, adiabatic flame temperatures and expressions that correlate measured NOx emissions with the flame temperature. Execution times are less than 10 seconds on a 486-66 MHz PC.

Heating neat (100 percent) methanol fuel (M100) is shown to improve dramatically the atomization of the fuel from a production, automotive, port fuel injector of pintle design. This improvement is particularly noticeable and important when compared with atomization at low fuel temperatures, corresponding to those conditions where cold-start is a significant problem with neat methanol-fueled (M100) vehicles. The improved atomization is demonstrated with photographs and laser-diffraction measurements of the drop-size distributions. Fuel temperatures were varied from -34°C (-29°F to 117°C (243°F), while the boiling point of methanol is 64.7°C (148.5°F). Air temperatures were ambient at about 24°C (75°F). For temperatures above the boiling point, some flash boiling and vaporization were presumably occurring, and these may have contributed to the atomization, but the trends for drop size did not shown any discontinuity near the boiling point.

The purpose of this work was to develop a series of octane reference fuels for road testing methanol fueled vehicles. Preliminary attempts to measure the research octane number of neat methanol by the standard ASTM test procedure produced anomalous results. This led to a more basic method of measuring the octane number based on the incipient knock compression ratio. The incipient knock method gave research and motor octane numbers of 112 and 88, respectively, for neat methanol. Research octane numbers of several methanol reference fuel blends prepared by adding octane enhancers and depressors were determined. The effects of spark timing and air/fuel mixture temperature on the incipient knock compression ratio of neat methanol were also examined.

Several investigations have shown that the operation of spark ignition engines on methanol can cause unusually high levels of wear during conditions of warm-up and cold-weather operation. This engine wear occurs principally in the upper cylinder bore and ring are as, and corrosion plays an important role in the mechanism. The present study examines the theory that the corrosion is caused by combustion residues that form when liquid alcohol on the cylinder wall evaporates and burns. Combustion residues were found when shallow pools of alcohol fuels were burned in an apparatus designed to simulate a water-cooled cylinder wall. The residues contained water, alcohol, formaldehyde, acetaldehyde, formic acid, acetic acid, and methylenehydroxy-peroxide; they reacted rapidly with cast iron to form iron formate and FeO(OH). This study explains previous test results on cylinder bore and ring wear in methanol and ethanol fueled engines.