André L. Boehman

An Experimental Investigation of the Origin of Increased NOx Emissions When Fueling a Heavy-Duty Compression-Ignition Engine with Soy Biodiesel

It is generally accepted that emissions of nitrogen oxides (NOx) increase as the volume fraction of biodiesel increases in blends with conventional diesel fuel. While many mechanisms based on biodiesel effects on in- cylinder processes have been proposed to explain this observation, a clear understanding of the relative importance of each has remained elusive. To gain further insight into the cause(s) of the biodiesel NOx increase, experiments were conducted in a single- cylinder version of a heavy-duty diesel engine with extensive optical access to the combustion chamber. The engine was operated using two biodiesel fuels and two hydrocarbon reference fuels, over a wide range of loads, and using undiluted air as well as air diluted with simulated exhaust gas recirculation. Measurements were made of cylinder pressure, spatially integrated natural luminosity (a measure of radiative heat transfer), engine-out emissions of NOx and smoke, flame lift-off length, actual start of injection, ignition delay, and efficiency. Adiabatic flame temperatures for the test fuels and a surrogate #2 diesel fuel also were computed at representative diesel-engine conditions. Results suggest that the biodiesel NOx increase is not quantitatively determined by a change in a single fuel property, but rather is the result of a number of coupled mechanisms whose effects may tend to reinforce or cancel one another under different conditions, depending on specific combustion and fuel characteristics. Nevertheless, charge-gas mixtures that are closer to stoichiometric at ignition and in the standing premixed autoignition zone near the flame lift- off length appear to be key factors in helping to explain the biodiesel NOx increase under all conditions. These differences are expected to lead to higher local and average in-cylinder temperatures, lower radiative heat losses, and a shorter, more-advanced combustion event, all of which would be expected to increase thermal NOx emissions. Differences in prompt NO formation and species concentrations resulting from fuel and jet-structure changes also may play important roles.

IMPACT OF ALTERNATIVE FUELS ON SOOT PROPERTIES AND DPF REGENERATION

Abstract In this work, fuel formulation exerted a strong influence on the properties of diesel particulates leading to differences in oxidation rate. These differences were especially significant when comparing soot derived from the combustion of soybean oil-derived biodiesel fuel (B100) and soot obtained from combustion of a Fischer–Tropsch diesel fuel (FT). These 2 fuels mainly differ in fuel oxygen content. Although B100 soot possesses an initially ordered structure, it is 5 times more oxidatively reactive than FT soot. While the initial structure alone does not dictate the reactivity of diesel soot, the relative amount of initial oxygen groups is the more important factor governing the oxidation rate than the initial structure and pore size distribution. Therefore, incorporation of greater surface oxygen functionality in the B100 soot provides the means for more rapid oxidation and thereby enables efficient regeneration of the diesel particulate filter.

Combustion of Syngas in Internal Combustion Engines

The combustion of synthesis gas will play an important role in advanced power systems based on the gasification of fuel feedstocks and combined cycle power production. While the most commonly discussed option is to burn syngas in gas turbine engines, another possibility is to burn the syngas in stationary reciprocating engines. Whether spark ignited or compression ignited, syngas could serve to power large bore stationary engines, such as those presently operated on natural gas. To date, however, there has been little published on the combustion of syngas in reciprocating engines. One area that has received attention is dual-fueled diesel combustion, using a combination of diesel pilot injection and syngas fumigation in the intake air. In this article, we survey some of the relevant published work on the use of synthesis gas in IC engines, highlighting recent work on dual-fuel (syngas + diesel) combustion.

Combustion and emissions performance of low sulfur, ultra low sulfur and biodiesel blends in a DI diesel engine

Experiments were conducted with a commercially available six-cylinder, 4-valves per cylinder, turbocharged, direct injection (Dl) diesel engine. The engine was operated with low sulfur diesel fuel, ultra low sulfur diesel fuel and two other blends, low sulfur diesel fuel with 20 wt.% biodiesel and ultra low sulfur diesel fuel with 20 wt.% biodiesel, to investigate the effect of the base fuels and their blends on combustion and emissions. Combustion analysis, particulate matter emissions and exhaust gas composition (CO, NO x and total hydrocarbons) were determined at eight steady-state operating conditions according to the AVL 8-Mode test protocol. Combustion analysis showed at high load conditions a retarded start of injection, an earlier start of combustion and a lower premixed burn peak with ultra low sulfur diesel fuel. Mode averaged NO x emissions decreased with ultra low sulfur diesel fuel and biodiesel blends compared to low sulfur diesel fuel. A 20% PM reduction was observed with ultra low sulfur (15 PPM) diesel fuel compared to low sulfur (325 PPM) diesel fuel.

Effects of oxygenated blending compounds on emissions from a turbocharged direct injection diesel engine

Abstract An experimental investigation was conducted to evaluate the effect of three different oxygenated compounds, diglyme, diethyl maleate and dibutyl maleate, on emissions from a Volkswagen 1.9 litre, turbocharged, direct injection diesel engine. Sampling was performed using a mini-dilution tunnel technique to obtain particulate matter and a Fourier transform infrared (FTIR) spectrometer for gaseous emissions. The particulate samples were analysed using thermal analysis and Soxhlet extraction to determine the fraction of volatile and soluble organic material respectively. All three oxygenated compounds were found to be effective at reducing particulate emissions, with the maleate compounds being more effective overall than the diglyme. Analysis of the relative contributions of changes in the soot and soluble organic fraction (SOF) to the reduction of particulate matter indicated that, for diethyl maleate and diglyme, reductions in soot were the dominant effect. No consistent trends in NOx emissions were observed, although the diethyl maleate, which was most effective at reducing the particulate matter, increased the NOx slightly at most of the test conditions. Differences in the combustion chemistry of the additives are discussed as a possible explanation of the greater effectiveness of the maleate compounds in reducing soot, as well as for the difference in the effectiveness of diethyl and dibutyl maleate.

Spray and combustion visualization of a direct-injection diesel engine operated with oxygenated fuel blends

Abstract Experiments were conducted with a commercially available six-cylinder water-cooled turbocharged direct-injection diesel engine. The cylinder head was modified to permit access to the combustion chamber with an engine videoscope. The engine was operated with base diesel fuel (BP-15) and other blends, base diesel with 20 wt% biodiesel (B-20) and with 20wt% diglyme (O-20). A neat biodiesel (B-100) and a 95 wt% blend of diglyme with base diesel fuel (O-95) were also considered. These fuels were used for observing the effect of the fuel properties on injection timing, heat release, flame structure, and luminosity. All the tests were performed with the engine operated at light load (61 N m, 10 per cent of the rated load) and 1800 r/min. Visualization showed that the start of injection occurred 0.4° earlier with B-100 than with BP-15. B-100 showed the earliest start of injection among the fuels. An earlier start of injection was also observed with B-20 and O-20 blends compared with BP-15 fuel. Combustion analysis showed a lower premixed combustion heat release rate with the diglyme blends compared with the B-20, B-100, and BP-15. The highest premixed burn peak and the lowest premixed burn peak were observed with BP-15 and O-95 fuels respectively. It is difficult to distinguish between the spray flames of BP-15, B-20, B-100, and O-20. However, with much higher oxygen content in the O-95 fuel the natural luminosity of the flame was too faint for detection with the camera. The combination of combustion analysis and in-cylinder visualization employed in this study provides a unique opportunity to understand how oxygenates behave in a commercial engine.

Conversion of various hydrocarbons over supported Pd during simulated cold-start conditions

This paper reports measured oxidation rates of synthetic automotive exhausts over an aged palladium (Pd) catalyst during simulated cold-start conditions. Surface reaction rates and species concentration profiles at points along a catalyst of Pd on Al2O3 with ceria are reported for A/F ratios from 10 to 16. The synthetic exhaust streams contain levels of carbon monoxide and hydrocarbons like those in auto exhausts during a cold-start, and include representative amounts of CO, CO2, O2, H2, NO, SO2 and H2O in N2. The hydrocarbon compounds are represented by 1-butene as a surrogate for the most reactive hydrocarbons, and propane and methane as surrogates for species with intermediate and very low reactivities, respectively. The data reveal important features of multicomponent oxidation under fuel-rich conditions. First, as expected, hydrogen is the most reactive species, reaching diffusion-limited oxidation at the inlet of the reactor for a temperature of 320°C, even for exhaust streams with 500 ppm NO. Second, the oxidation of carbon monoxide and 1-butene over an aged palladium catalyst follows similar conversion histories for excessively fuel rich and near-stoichiometric conditions. Third, the hydrocarbons oxidize simultaneously, but at rates that follow the ranking of reactivities seen in tests with individual fuel species. Whereas the magnitude of the 1-butene conversion rate is much lower than carbon monoxides because of its much lower inlet level, this hydrocarbon is eliminated on nearly the same time scale as carbon monoxide. But propane and methane are converted on much longer time scales. Fourth, the oxidation of all the fuel species is inhibited by the presence of nitric oxide in the feedstream, especially propane.

Impact of rail pressure and biodiesel fueling on the particulate morphology and soot nanostructures from a common-rail turbocharged direct injection diesel engine

An investigation of the impact of rail pressure and biodiesel fueling on exhaust particulate agglomerate morphology and primary particle (soot) nanostructure was conducted with a common-rail turbocharged direct injection diesel engine. The engine was operated at steady state on a dynamometer running at moderate speed with both low (30%) and medium–high (60%) fixed loads, and exhaust particulate was sampled for analysis. The fuels used were ultra-low sulfur diesel and its 20% v/v blends with soybean methyl ester biodiesel. Fuel injection occurred in a single event around top dead center at three different injection pressures. Exhaust particulate samples were characterized with transmission electronic microscopy imaging, scanning mobility particle sizing, thermogravimetric analysis, Raman spectroscopy, and X-ray diffraction analysis. Particulate morphology and oxidative reactivity were found to vary significantly with both rail pressure and biodiesel blend level. Higher biodiesel content led to an increase in the primary particle size and oxidative reactivity but had no impact on nanoscale disorder in the as-received samples. For particulates generated with higher injection pressures, the initial oxidative reactivity increased, but there was no detectable correlation with primary particle size or nanoscale disorder.

Experimental Study of Oxygen-Enriched Diesel Combustion Using Simulated Exhaust Gas Recirculation

The techniques of design of experiments were applied to study the best operational conditions for oxygen-enriched combustion in a single-cylinder direct-injection diesel engine in order to reduce particulate matter (PM) emissions, with minimal deterioration in nitrogen oxide (NO x ) emissions, by controlling fuel injection timing, carbon dioxide (CO 2 ) and O 2 volume fractions in intake air. The results showed that CO 2 addition reduced average combustion temperatures and minimized the rate of increase in NO x emissions observed during oxygen-enriched conditions. It was also observed that oxygen enrichment minimized the deterioration in brake-specific fuel consumption and hydrocarbon and PM emissions that occurred at the highest level of CO 2 addition.

Development of a Dimethyl Ether (DME)-Fueled Shuttle Bus

Dimethyl Ether (DME) is a potential ultra-clean diesel fuel. Its unique characteristics require special handling and accommodation of its low viscosity and low lubricity. In this project, DME was blended with diesel fuelto provide sufficient viscosity and lubricity to permit operation of a 7.3 liter turbodiesel engine in a campus shuttle bus with minimal modification of the fuel injection system. A pressurized fuel delivery system was added to the existing common rail injection system on the engine, allowing the DME-diesel fuel blend to be circulated through the rail at pressures above 200 psig keeping the DME in the liquid state. Fuel exiting the rail is cooled by finned tubed heat exchangers and recirculated to the rail using a gear pump. A modified LPG tank (for use on recreational vehicles) stores the DME- diesel fuel blend onboard the shuttle bus. A small cylinder of helium is used to provide a blanket of inert gas above the fuel mixture to keep the DME in the liquid state and to push the mixture to the fuel rails. A significant challenge is posed by the rapid increase in DME vapor pressure with increasing fuel temperature. As the fuel mixture passes through the rail, it is heated by the surrounding surfaces in the cylinder head. The target for maximum fuel rail temperature was set at 50°C, which corresponds to a DME vapor pressure of 150 psig. Refueling was accomplished by mixing the diesel fuel and DME onboard the bus, with diesel fuel delivered from the existing diesel tank and DME delivered by 1000 Ib cylinders at a small refueling station. The shuttle bus operates on the Faculty/Staff loop at the University Park campus of the Pennsylvania State University.