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Particle formation, growth, coagulation and combustion in the cylinder of an indirect injection passenger car type diesel engine have been studied using a system which allows the cylinder contents to be rapidly expelled through a blowdown port, diluted, and collected in a sample bag for subsequent analysis. Characteristic blowdown times were about 0.5 ms. Samples were analyzed using a condensation nuclei counter to determine particle number concentrations and an electrical aerosol analyzer to determine particle volume concentrations in the 0.01 to 1.0 μm diameter range. Measurements were made with the engine operating at 1000 rpm and an equivalence ratio of 0.32. Peak particle number concentration in the cylinder 13 times the exhaust level, and peak particle volume (or mass) concentration in the cylinder 3 times the exhaust level were observed. These results suggest that significant particle coagulation and oxidation occur during the expansion stroke.

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.

The U.S. Bureau of Mines has sponsored research Co determine the particle size distribution and concentration of submicron particles upstream and downstream of a ceramic particle trap mounted in the exhaust stream of a Caterpillar 3304 diesel engine. Particle size distribution and mass were measured with an electrical aerosol analyzer, a diffusion battery-condensation nuclei counter combination, and filters. The engine was operated at 1400 and 1800 RPM and 3 load conditions at each speed-In general, the collection efficiency of the trap was high, ranging between 89 to 96%. Size distribution analysis revealed that the trap was generally more efficient at removing particles smaller than 0.1 µm diameter than larger particles. However, under certain conditions formation of nuclei (less than 0.056 µm diameter) downstream of the trap took place.

Earlier work [1] shows that kinetics of Diesel soot oxidation is different from that of ethylene diffusion flame soot oxidation [2], possibly due to metals from lube oil. This study investigates the influence of metals on soot oxidation and the exhaust particle emissions using lube oil dosed fuel (2 % by volume). This method does not simulate normal lube oil consumption, but is used as a means of adding metals to particles for oxidation studies. This study also provides insight into the effect of systems that mix lube oil with fuel to minimize oil change service. The HTO-TDMA (High Temperature Oxidation-Tandem Differential Mobility Analyzer) technique [1] was used to measure the surface specific oxidation rate of Diesel particles over the temperature range 500-750 °C. Diesel particles sampled from the exhaust stream of a Diesel engine were size segregated by differential mobility and oxidized in situ in air in a heated flow tube of known residence time and temperature profile.

Soot is the largest component of contaminants found in the diesel engine lubricating oil. The soot enters lubricating oil mainly through thermophoretic deposition on the cylinder wall. Although the mechanism is still not fully understood, it is generally accepted that soot particles promote engine wear, reducing engine component service life, fuel efficiency and performance. This problem will be further exacerbated when more and more diesel engines use EGR to reduce NOx emissions and when lubricating oil consumption is drastically reduced to control particulate emissions. In this study, lubricating oil samples were taken from 7 different operating diesel engines. The size distribution and concentration of the diesel soot particles in the lubricants were investigated by methods of photosedimentation and quantitative spectrophotometry. The size distributions were compared to those of soot particles in the exhaust.

The effects of fuel sulfur content and dilution conditions on diesel engine PM number emissions have been researched extensively through steady state testing. Most results show that the concentration of nuclei-mode particles emitted increases with fuel sulfur content. A few studies further observed that fuel sulfur content has little effect on the emissions of heavily-used engines. It has also been found that primary dilution conditions can have a large impact on the size and number distribution of the nuclei-mode particles. These effects, however, have not yet been fully understood through transient testing, the method used by governments worldwide to certify engines and regulate emissions, and a means of experimentation which generates realistic conditions of on-road vehicles by varying the load and speed of the engine.

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.

There is a growing body of evidence that in-cylinder surfaces play an important role in determining the nature and quantity of soot emitted by diesel engines. This paper describes recent experimental results which demonstrate the importance of both the deposition of soot on walls during the combustion process and its subsequent reentrainment during exhaust blowdown. Soot deposition was demonstrated both experimentally and theoretically. The principal mechanism of soot deposition during combustion is thermophoresis. Our results suggest that the gross rate of in-cylinder deposition in the indirect injection diesel engine is between 20 and 45 percent of the net soot emission rate. Thus, a significant fraction of the soot emitted may have been stored on combustion chamber surfaces and protected from oxidation. Further evidence of wall deposition and subsequent reentrainment has been obtained by making time-resolved measurements of soot concentrations in the exhaust.

Time resolved primary and agglomerate particle size distribution measurements have been made on samples obtained from within the cylinder and from the exhaust of a single-cylinder modification of a 2.8 liter displacement, four-cylinder, naturally-aspirated, high swirl, direct-injection diesel engine. The total cylinder sampling method has been used to sample, quench, and dilute the entire contents of the cylinder in about 1 ms. Experiments have been performed at an equivalence ratio of 0.7 and a speed of 1000 RPM. An electrostatic aerosol sampler and a transmission electron microscope have been used to determine primary and agglomerate particle size distributions for both in-cylinder and exhaust samples. An electrical aerosol analyzer and a diffusion battery followed by a condensation nucleus counter were used to further characterize the agglomerate size distributions of exhaust samples.

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.

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.

Vibration signals from diesel engines were analyzed for the purpose of isolating signals relating to injection or combustion which could be used to time the engines. Nonintrusive sensors, magnetically attached to the engine, were used to obtain these vibration signals. Components believed to be associated with combustion or fuel injection were electronically isolated from the remaining engine noise, and subsequently processed to produce specific timing signals. Digital data acquisition and averaging methods were used, coupled with computerized frequency analysis. The signals were experimentally correlated with the combustion process over a wide range of injection timing. The electronic processing system developed provides a real time digital measure of the timing. Data on the accuracy and correlation of experimental measurements will be presented.

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.

The formation of NO2 in the cylinder of a diesel engine has been investigated using a total cylinder sampling technique and a simple kinetic model. Exhaust measurements of NO2 as a function of equivalence ratio and as function of time after engine start were made. Samples obtained by total cylinder sampling from an operating direct injection diesel engine showed NO2/NO ratios of 25 to 50%. This is much higher than the 1 to 3% which was measured in the exhaust. Simulations of the sampling process indicate that conversion of NO to NO2 is at least partially responsible for the high NO2/NO measurements. However, the processes which produce the NO to NO2 conversion during the sampling also occur during normal combustion. This may lead to high NO2 concentrations during the combustion cycle which are then lowered during the expansion to the measured exhaust concentrations.

A unique system which allows sampling of the entire contents of one of the cylinders of a 5.7-liter V-8 indirect-injection diesel engine has been developed. An explosively actuated cutter ruptures a diaphragm in the combustion chamber and allows the contents of the cylinder to rush out and be subsequently diluted and quenched with cool nitrogen. Particles are collected with a high-volume impactor/filter system. This system has been used to collect a series of particle samples at crankangles ranging from 5 to 40 degrees after top dead center. Particle samples from the exhaust were also obtained. The samples have been extracted to determine the soluble organic fraction. These extracts have been analyzed for five polycyclic aromatic compounds: pyrene, fluoranthene, benz(a)pyrene, benz(k)fluoranthene, and 1-nitropyrene. The results indicate significant removal of the first four between the combustion chamber and the exhaust manifold.

Light absorption and scattering coefficients have been measured for particles emitted by two diesel engines; one direct injection and one indirect injection, operating over a range of speeds and loads. Integrating plate absorption measurements yield a specific absorption coefficient of 9.1 square meters per gram of non-volatile particulate matter at 550 nm wavelength. This absorption coefficient is inversely proportional to wavelength and independent of engine operating conditions or type. The scattering coefficient was simultaneously measured as 1.3 square meters per gram of undifferentiated particulate matter. These experimental results are shown to be in the range predicted by theoretical absorption and scattering calculations, which have been made for elongated carbon-void particles.

The formation of particles in the combustion chamber of a direct injection diesel engine has been studied with the use of the Total Cylinder Sampling Method. With this method, nearly the entire contents of the cylinder of an operating diesel engine can be quickly removed at various times during the combustion process. The particle mass and size distributions present in the sample can then be analyzed. If quenching of the combustion process is quick and complete, the resulting samples are representative of the particle mass and size distributions present in the cylinder near the time sampling begins. This paper discusses the effect of injection timing and piston bowl shape on the particle formation and oxidation. Example size distribution measurements are also shown. The particle concentrations in the cylinder were measured for three different injection timings with the standard piston installed in the engine.

This report describes tests of a fuel additive in a medium-duty, high-swirl, direct-injection diesel engine. The additive was found to have little influence on general combustion performance or on NOx emissions. On the other hand, it had a profound effect on particulate emissions. This was most clear under high load where particle emissions are highest. Here, when the engine was switched from running on the base fuel to the additive treated fuel, particle emissions at first increased and then fell to levels about 40% lower (by particle volume) than those initially produced by the base fuel. The additive had a long lasting effect. After running with the additive for about 25 hours, emission levels with the base fuel were only slightly higher than those with the additive treated fuel. We believe that the additive action is associated with a combination of cleaning and surface conditioning. More work should be done to understand the relative importance of these two mechanisms.

In-cylinder and exhaust soot mass measurements have been made on a single-cylinder conversion of a 4-cylinder, 2.8 1, high-swirl, direct-injection diesel engine using a sampling system which allows dumping, diluting, quenching, and collecting the entire contents of the cylinder on a time scale o£ about 1 ms. Experiments have been performed at engine speeds of 1,000 and 1,500, and equivalence ratios, ϕ, of 0.4 and 0.7. Soot mass first appears shortly after top dead center and reaches a peak between 15 and 30 crankangle degrees after top dead center (CAD ATDC). After reaching its peak value, soot concentration decreases with increasing crankangle and approaches exhaust levels by 40-60 CAD ATDC. The time lag between the start of combustion and the first appearance of soot increases with ϕ and ranges from 0.2 to 1 ms. The initial rate of soot formation ranges from 0.26 to 0.30 mg ms−1 and varies little with speed or ϕ.

Measurements of particle concentrations in one cylinder of a 1982 5.7 liter GM V-8 diesel engine have been made using a unique total cylinder sampling system. The first part of the paper is devoted to an examination of the performance of the sampling system. The role of blowoff and nucleation in the formation of sample artifacts is discussed. The remainder of the paper is devoted to the results of a study of the formation and removal of carbon particles during diesel engine combustion. Several operating conditions have been examined. The influence of injection timing, load, EGR, and oxygen addition on particle formation and removal has been investigated. The concentrations of volatile and nonvolatile particulate matter have been measured as a function of crankangle position. Particle formation begins 1-5 crankangle degrees (CAD) after the start of combustion.