Robert M. Siewert

Methane oxidation over alumina-supported noble metal catalysts with and without cerium additives

Laboratory reactor experiments have been conducted to evaluate alumina-supported noble metal catalysts, both in the presence and absence of cerium additives, for their effectiveness in the catalytic oxidation of methane under conditions likely to be encountered in natural-gas vehicle exhaust. Under oxidizing conditions, all of the catalysts promoted the complete oxidation of methane to CO2 and H2O, with the methane oxidation activity ranking given by Pd > Rh > Pt in the absence of Ce and by Rh > Pd ≈ Pt in the presence of Ce. Under reducing conditions, methane oxidation produced substantial amounts of CO and H2 as the principal partial oxidation products. In the absence of Ce, the methane oxidation activity decreases in the order Pd > Rh > Pt, with the tendency to form CO decreasing in the order Rh > Pd > Pt. The activity ranking for methane conversion in reducing feedstreams was not affected by the presence of Ce; however, the addition of Ce to the Pt/Al2O3 and Pd/Al2O3 catalysts almost completely suppressed the formation of the partial oxidation product CO. At a fixed temperature of ≈550°C, the methane conversion over each of the noble metal catalysts goes through a maximum as the feedstream concentration of O2 is varied. The data suggest that O2 inhibits the CH4 oxidation under oxidizing conditions by excluding the more weakly adsorbed species, CH4, from the active sites. Also, methane oxidation experiments in the presence of CO in the feed showed that the methane conversion characteristics of the noble metal catalysts are little affected by the CO.

Evaluation of a Narrow Spray Cone Angle, Advanced Injection Timing Strategy to Achieve Partially Premixed Compression Ignition Combustion in a Diesel Engine

Simultaneous reduction of nitric oxides (NOx) and particulate matter (PM) emissions is possible in a diesel engine by employing a Partially Premixed Compression Ignition (PPCI) strategy. PPCI combustion is attainable with advanced injection timings and heavy exhaust gas recirculation rates. However, over-advanced injection timing can result in the fuel spray missing the combustion bowl, thus dramatically elevating PM emissions. The present study investigates whether the use of narrow spray cone angle injector nozzles can extend the limits of early injection timings, allowing for PPCI combustion realization. It is shown that a low flow rate, 60-degree spray cone angle injector nozzle, along with optimized EGR rate and split injection strategy, can reduce engine-out NOx by 82% and PM by 39%, at the expense of a modest increase (4.5%) in fuel consumption. This PPCI strategy has the potential for meeting upcoming stringent fuel specific NOx emission levels of less than 1 g/kg-fuel and fuel specific PM levels less than 0.25 g/kg-fuel.

Unassisted Cold Starts to −29°C and Steady-State Tests of a Direct-Injection Stratified-Charge (DISC) Engine Operated on Heat Alcohols

Unassisted cold starts at ambient temperatures down to -29 degrees C were achieved on neat alcohols in a cold room using a 4.8-L direct- injection stratified-charge (DISC) engine with late fuel injection. Starting times for the United Parcel Service (UPS) stratified-charge engine were less than three seconds at -29 degrees C. Cold starts to -29 degrees C also were achieved with gasoline and diesel fuel. Additionally, an SAE OW oil was used as a fuel and started at -18 degrees C. A key to cold starting was achieving a minimum cranking speed (110 r/min) that ensured injection of fuel. Higher cranking speeds improved cold starting. Increased injection rate enhanced cold starting. For alcohol, the advantage of using a long-duration high- power ignition system was confirmed. The ability to fire and run was relatively independent of the wide range of fuel properties, including heat of vaporization, heat of combustion, and volatility. For the covering abstract see IRRD 853507.

The Variable Stroke Engine - Problems and Promises

The concept of the variable stroke engine (VSE) is explained and problems related to its use are discussed. Single-cylinder combustion data are combined with published multi-cylinder VSE friction data to formulate an engine model. This engine model is coupled with a vehicle model to project 55/45 fuel economy (based on Environmental Protection Agency urban/highway schedule calculations) and NOx (nitrogen oxides) gm/mi which are compared with similar projections for a throttled engine. At an NOx level of 0.93 gm/km (1.5 gm/mi), VSE fuel economy improvements ranged from 2% to 20%, depending upon the frictional losses and the vehicle power-to-weight ratios used in the models (the higher the ratio, the greater the improvement). The calculations suggest that with the VSE, the lower the NOx level, the less the fuel economy improvement. Variable displacement engines using cylinder deactivation have been projected to offer fuel economy improvement competitive with that of the VSE.

THE STAGED COMBUSTION COMPOUND ENGINE (SCCE): EXHAUST EMISSIONS AND FUEL ECONOMY POTENTIAL

Experiments with a two-cylinder research engine showed that low NO emission could be obtained without sacrificing engine efficiency. However, approximately 40 percent more displacement is required to produce the same power as conventional SI engines. The sources of HC, CO, and NO emissions were investigated, as were the effects of major engine variables on these exhaust emissions and fuel consumption. The staged combustion concept was implemented using a 7.46 litre V-8 engine. Present FTP emission levels are 0.87 g/mi HC, 8.7 g/mi CO, and 0.34 g/mi NO at low mileage using a catalytic converter. FTP fuel economy is 4.9 km/2 (11.5 mpg). /GMRL/