Search Results

Four-way, integrated, diesel emission control systems that combine selective catalytic reduction for NOx control with a continuously regenerating trap to remove diesel particulate matter were evaluated under real-world, on-road conditions. Tests were conducted using a semi-tractor with an emissions year 2000, 6-cylinder, 12 L, Volvo engine rated at 287 kW at 1800 rpm and 1964 N-m. The emission control system was certified for retrofit application on-highway trucks, model years 1994 through 2002, with 4-stroke, 186-373 kW (250-500 hp) heavy-duty diesel engines without exhaust gas recirculation. The evaluations were unique because the mobile laboratory platform enabled evaluation under real-world exhaust plume dilution conditions as opposed to laboratory dilution conditions. Real-time plume measurements for NOx, particle number concentration and size distribution were made and emission control performance was evaluated on-road.

Diesel exhaust particle number concentrations and size distributions, as well as gaseous and particulate mass emissions, were measured during steady-state tests on a US heavy-duty engine and a European passenger car engine. Two fuels were compared, namely a Fischer-Tropsch diesel fuel manufactured from natural gas, and a US D2 on-highway diesel fuel. With both engines, the Fischer-Tropsch fuel showed a considerable reduction in the number of particles formed by nucleation, when compared with the D2 fuel. At most test modes, particle number emissions were dominated by nucleation mode particles. Consequently, there were generally large reductions (up to 93%) in the total particle number emissions with the Fischer-Tropsch fuel. It is thought that the most probable cause for the reduction in nucleation mode particles is the negligible sulphur content of the Fischer-Tropsch fuel. In general, there were also reductions in all the regulated emissions with the Fischer-Tropsch fuel.

A one-stage dilution tunnel has been developed to sample and dilute diesel exhaust. The tunnel has the capability of simulating many aspects of the atmospheric dilution process. The dilution rate and overall dilution ratio, temperature, relative humidity, and residence time in the tunnel, as well as residence time and temperature in the transfer line between the tunnel and exhaust sampling point may be varied. In this work we studied the influence of the exhaust transfer line, tunnel residence time, and dilution air temperature on the exhaust particle size distribution. The influences of fuel sulfur content on the size distribution and on the sensitivity of the size distribution to dilution and sampling conditions were also examined. We do not suggest an optimum dilution scheme, but do identify critical variables.

Nanoparticle formation during exhaust sampling and dilution has been examined using a two-stage micro-dilution system to sample the exhaust from a modern, medium-duty diesel engine. Growth rates of nanoparticles at different exhaust dilution ratios and temperatures have been determined by monitoring the evolution of particle size distributions in the first stage of the dilution system. Two methods, graphical and analytical, are described to determine particle growth rate. Extrapolation of size distribution down to 1 nm in diameter has been demonstrated using the graphical method. The average growth rate of nanoparticles is calculated using the analytical method. The growth rate ranges from 6 nm/sec to 24 nm/sec, except at a dilution ratio of 40 and primary dilution temperature of 48 °C where the growth rate drops to 2 nm /sec. This condition seems to represent a threshold for growth. Observed nucleation and growth patterns are consistent with predictions of a simple physical model.

A system has been developed that allows near real time measurements of total, volatile, and nonvolatile particle concentrations in engine exhaust. It consists of a short section of heated catalyst, a cooling coil, and an electrical aerosol analyzer. The performance of this catalytic stripper system has been characterized with nonvolatile (NaCl), volatile sulfate ((NH4)2 SO4), and volatile hydrocarbon (engine oil) particles with diameters ranging from 0.05-0.5 μm. The operating temperature of 300°C gives essentially complete removal of volatile sulfate and hydrocarbon particles, but also leads to removal of 15-25% of solid particles. This system has been used to determine total, volatile, and nonvolatile particle concentrations in the exhaust of a Diesel engine and a spark ignition engine. Volatile volume fractions measured in Diesel exhaust with the catalytic stripper system increased from 19-65% as the equivalence ratio (load) decreased from 0.64-0.13.

A study of factors affecting hydrocarbon oxidation in a diesel oxidation catalyst was undertaken. The objective was to determine whether interactions between particulate-adsorbed hydrocarbons and the catalyst significantly influenced hydrocarbon oxidation. Theoretical modeling supported by experimental data obtained at the U.S. Bureau of Mines' Diesel Emissions Research Laboratory indicated that the mass of particles interacting with the ceramic support was negligible. Additionally, a model of hydrocarbon adsorption onto diesel particulate predicted that over 98% by mass of exhaust hydrocarbons would be gas-phase, rather than particulate-adsorbed, at converter operating temperatures. A second physical process, the diffusion of gas phase hydrocarbons to the catalytic surface, was subsequently investigated. Theoretical and experimental results for the unburnt fuel hydrocarbons indicated that hydrocarbon oxidation was diffusion limited under high temperature operating conditions.

Carbon black particles, which morphologically and chemically simulate a diesel exhaust soot, were mixed with the intake air of a single-cylinder direct injection diesel engine to investigate the efficiency of their removal by oxidation in the combustion chamber. An aerosol generation system, which is capable of generating carbon black aerosol of a size distribution and mass flow rate comparable to those of the soot agglomerates, was developed first. The aerosol was then introduced into the engine which was operating on conventional fuel. Four methods were used to characterize the exhaust particles: an electrical aerosol analyzer, a condensation nuclei counter, a low volume filter, and a micro-orifice cascade impactor. The size distribution and concentration of the diesel soot particles in the lubricants were investigated by methods of photosedimentation and quantitative spectrophotometry, respectively.

A major problem with many soot emission control devices is the fact that they quickly become loaded with soot which must be removed by a controlled burning (regeneration) process. The need for regeneration greatly complicates such diesel particle emission control devices. In this paper, an electrostatic agglomerator (ESA) which efficiently collects diesel particles but does not require regeneration is described. The ESA is an electrostatic precipitator which is designed to collect and subsequently reentrain diesel soot particles. The collection and reentrainment processes results in growth of particle diameter from roughly 0.2 μm to larger than 1.0 μm. The agglomerated particles are large enough to be collected by a relatively simple inertial device, e.g., a cyclone separator. The collected particle may be either recycled to the engine or disposed of by other means. Electrostatic collection is made easier by the fact that diesel particles are charged by the combustion process itself.

This study examines the effect of a ceramic particle trap and a manganese fuel additive on the mutagenic activity and chemical composition of diesel exhaust particulate matter from a heavy-duty mining engine. Particles were collected by dilution tunnel sampling from a 4-cylinder, Caterpillar 3304, naturally-aspirated, indirect-injection engine operated at six steady-state conditions. Depending on engine load and speed the ceramic particle trap reduced the following emissions: particulate matter, 80 – 94%; soluble organic fraction (SOF), 83 – 95%; 1-nitropyrene, 94 – 96%; and SOF mutagencity, 72% (cycle-weighted average). When the Mn fuel additive was used without a ceramic particle trap the total cycle mutagenic activity emitted increased 7-fold, in part, due to elevated emissions of 1-nitropyrene.

This paper describes an examination of the origin of the response of a real-time exhaust particle sensor. The sensor works by detecting the net electrical charge carried by diesel exhaust particles emitted during exhaust blow-down. The distribution of charge on these particles has been measured using an electrical mobility analysis system. The results show that the exhaust particles are highly charged and that their charge distributions are nearly symmetrical. The sensor signal results from a slight departure from this symmetry. The results suggest that most of the charge on the exhaust particles results from bipolar charging by flame ions during combustion, but that the net charge detected by the sensor results from surface interactions which some of the larger particles undergo during exhaust blowdown.

Particle mass and size distribution measurements have been made on the exhaust of an Onan prechamber diesel engine. Seven fuels were examined: no. 1 and no. 2 diesel fuel, 40 and 50 cetane number secondary reference fuels, and no. 2 diesel fuel doped with three different concentrations of Lubrizol 565, a barium-based smoke suppressant. The no. 1 and no. 2 diesel fuels and the 50 cetane number reference fuels produced very similar emissions with emission indices in the range 0.3-1.3 mg (gm-fuel)-1 and volume mean diameters between .09 and 0.15 μm. The 40 cetane number reference fuel produced both smaller emission indices, 0.2 to 0.8 mg (gm-fuel)-1, and particle diameters, 0.03 to 0.09 μm. These reductions were apparently related to the longer ignition delay period of the 40 cetane number fuel, which allowed better mixing of the fuel and air prior to combustion.