Showing papers on "Diesel engine published in 1996"

Mechanism of Soot and NOx Emission Reduction Using Multiple-injection in a Diesel Engine

Abstract: Engine experiments have shown that with highpressure multiple injections (two or more injection pulses per power cycle), the soot-NOx trade-off curves of a diesel engine can be shifted closer to the origin than those with the conventional single-pulse injections, reducing both soot and NOx emissions significantly. In order to understand the mechanism of emissions reduction, multidimensional computations were carried out for a heavy-duty diesel engine with multiple injections. Different injection schemes were considered, and the predicted cylinder pressure, heat release rate and soot and NOx emissions were compared with measured data. Excellent agreements between predictions and measurements were achieved after improvements in the models were made. The improvements include using a RNG k-e turbulence model, adopting a new wall heat transfer model and introducing the nozzle discharge coefficient to account for the contraction of fuel jet at the nozzle exit. The present computations confirm that split injection allows significant soot reduction with out a NOx penalty. Based on the computations, it is found that multiple injections have a similar NOx reduction mechanism as single injections with retarded injection timings. Regarding soot reduction, it is shown that reduced soot formation is due to the fact that the soot producing rich regions at the spray tip are not replenished when the injection is terminated and then restarted. With split injections, the subsequently injected fuel burns rapidly and does not contribute significantly to soot production. The present work also demonstrates the usefulness of multidimensional modeling of diesel combustion to reveal combustion mechanisms and to provide design insights for low emission engines. EXTENSIVE RESEARCH is in progress to reduce both nitrogen oxides (NOx) and particulate (soot) emissions from diesel engines due to environmental concerns. One of the emission-control strategies is in-cylinder reduction of pollutant production. It is well known that it is very difficult to reduce both NOx and soot production simultaneously during the combustion process. Many emission-reduction technologies developed so far tend to increase soot emission while reducing NOx emission, and vice versa. For example, retarding fuel injection timing can be effective to reduce NO formation. However, this usually results in an increase of soot production. On the other hand, although increasing fuel injection pressure can decrease soot emissions, it can also cause higher NOx emissions at the same time [1]*. Recently, it has been shown experimentally that with high-pressure multiple injections, the soot-NOx trade-off curves of a diesel engine can be shifted closer to the origin than those with single-pulse injections, reducing both soot and NOx emissions significantly [2-4]. Nehmer and Reitz experimentally investigated the effect of double-pulse split injection on soot and NOx emissions using a single-cylinder Caterpillar heavy-duty diesel engine [2]. They varied the amount of fuel injected in the first injection pulse from 10 percent to 75 percent of the total amount of fuel and found that split injection affected the sootNOx trade-off. In general, their split-injection schemes reduced NOx with only a minimal increase in soot emissions and did not extend the combustion duration. Tow et al. [3] continued the study of Nehmer and Reitz [2] using the same engine, and included different dwells between injection pulses and triple injection schemes in their investigation. They found that at high engine load (75%), particulate could be reduced by a factor of three with no increase in NOx and only a 2.5% increase in BSFC compared to a single injection, using a double injection with a relatively long dwell between injections. They also found that triple injection could reduce NOx and soot emissions at both light and high loads. Another important conclusion of Tow et al. [3] is that the dwell between injection pulses is very important to control soot production and there exits an optimum dwell at a particular engine operating condition. The optimum dwell of a double-injection was found to be about 10 degree crank angles at 75% load and 1600 rev/min for their engine conditions. * Numbers in brackets designate References at the end of the paper. Pierpont et al. [4] confirmed that the amount of fuel injected in the first pulse affects the particulate (smoke) level in experiments where the NOx emission level was held constant. However, the best double injections were found to also depend on the spray nozzle included angle. For a production injector with a 125 included angle, which results in significant wall impingement on the piston bowl, the best double injections were found to be those with 50% to 60% of the fuel injected in the first pulse. They also found that with a combination of EGR and multiple injections, particulate and NOx were simultaneously reduced to as low as 0.07 and 2.2 g/bhp-hr, respectively, at 75% load and 1600 rev/min. Other multiple injection studies can be also found in the open literature [5, 6]. The published experimental works indicate that multiple-injection is an effective mean to control NO and particulate production during the diesel combustion process. In general, multiple injections allow the injection timing to be retarded to reduce NOx emission while holding the particulate at low levels. Both the amount of fuel injected in the first pulse and the dwell between pulses are important for an optimum injection scheme. With the application of multiple injection technology, the goal of improved injection scheme design and better control of engine combustion is made difficult by the fact that design variables are added with flexible injectors. It is thus helpful to simulate the engine processes with the use of computational models, which can provide detailed temporal and spatial information of precisely parameter-controlled injection and combustion processes. Patterson et al. [7] performed multidimensional computations of multiple injections using an improved KIVA code. They tried to reproduce the experimental results of Nehmer and Reitz [2] and achieved a fair success. However, the accuracy of their model prediction deteriorated for double-pulse injections as the amount of fuel injected in the second pulse increased. Kong, Han and Reitz [8] modified the code by including a modified RNG k-e turbulence model and turbulence boundary conditions [9]. Predictions of combustion and emissions of single-injections were shown to be improved significantly [8]. These successes motivated the application of the code to multiple injections in the present study. It is clear that a good model is necessary in order to predict engine combustion and emissions accurately. Accordingly, the submodels used by Kong, Han and Reitz [8] were implemented together with improved heat transfer and injection models. The models were first applied to the experimental results of the double injections of Nehmer and Reitz [2]. For better understanding of the formation of NO and soot during multiple-injection combustion processes, a set of designed singleand double-injection schemes were computed. Based on the computational results, a mechanism of emission reduction using multiple-injection is suggested.

Elemental carbon-based method for occupational monitoring of particulate diesel exhaust: methodology and exposure issues.

Abstract: Diesel exhaust has been classified a probable human carcinogen, and the National Institute for Occupational Safety and Health (NIOSH) has recommended that employers reduce workers' exposures. Because diesel exhaust is a chemically complex mixture containing thousands of compounds, some measure of exposure must be selected. Previously used methods involving gravimetry or analysis of the soluble organic fraction of diesel soot lack adequate sensitivity and selectivity for low-level determination of particulate diesel exhaust; a new analytical approach was therefore needed. In this paper, results of investigation of a thermal–optical technique for the analysis of the carbonaceous fraction of particulate diesel exhaust are discussed. With this technique, speciation of organic and elemental carbon is accomplished through temperature and atmosphere control and by an optical feature that corrects for pyrolytically generated carbon, or ‘char,’ which is formed during the analysis of some materials. The thermal–optical method was selected because the instrument has desirable design features not present in other carbon analysers. Although various carbon types are determined by the method, elemental carbon is the superior marker of diesel particulate matter because elemental carbon constitutes a large fraction of the particulate mass, it can be quantified at low levels and its only significant source in most workplaces is the diesel engine. Exposure-related issues and sampling methods for particulate diesel exhaust also are discussed.

Fuel Properties and Emissions of Soybean Oil Esters as Diesel Fuel

Abstract: The effects of using blends of methyl and isopropyl esters of soybean oil with No. 2 diesel fuel were studied at several steady-state operating conditions in a four-cylinder turbocharged diesel engine. Fuel blends that contained 20, 50, and 70% methyl soyate and 20 and 50% isopropyl soyate were tested. Fuel properties, such as cetane number, also were investigated. Both methyl and isopropyl esters provided significant reductions in particulate emissions compared with No. 2 diesel fuel. A blend of 50% methyl ester and 50% No. 2 diesel fuel provided a reduction of 37% in the carbon portion of the particulates and 25% in the total particulates. The 50% blend of isopropyl ester and 50% No. 2 diesel fuel gave a 55% reduction in carbon and a 28% reduction in total particulate emissions. Emissions of carbon monoxide and unburned hydrocarbons also were reduced significantly. Oxides of nitrogen increased by 12%.

The Dilution, Chemical, and Thermal Effects of Exhaust Gas Recirculation on Diesel Engine Emissions - Part 1: Effect of Reducing Inlet Charge Oxygen

Abstract: This is a first of a series of papers describing how the replacement of some of the inlet air with EGR modifies the diesel combustion process and thereby affects the exhaust emissions This paper deals with only the reduction of oxygen in the inlet charge to the engine (dilution effect) The oxygen in the inlet charge to a direct injection diesel engine was progressively replaced by inert gases, whilst the engine speed, fuelling rate, injection timing, total mass and the specific heat capacity of the inlet charge were kept constant The use of inert gases for oxygen replacement, rather than carbon dioxide (CO 2) or water vapour normally found in EGR, ensured that the effects on combustion of dissociation of these species were excluded In addition, the effects of oxygen replacement on ignition delay were isolated and quantified Results from final set of tests are also presented during which the inlet charge temperature was raised progressively to quantify the effect that EGR temperature has on combustion and emissions The reduction in the inlet charge oxygen (dilution effect) resulted in very large reductions in exhaust NO x level at the expense of rises in particulates and unburnt hydrocarbon emissions The engine power output and fuel economy also deteriorated substantially Raising the inlet charge temperature increases NOx but also, substantially, the exhaust smoke and particulate emissions © 1996 Society of Automotive Engineers, Inc

Effects on symptoms and lung function in humans experimentally exposed to diesel exhaust.

Abstract: OBJECTIVES: Diesel exhaust is a common air pollutant made up of several gases, hydrocarbons, and particles. An experimental study was carried out which was designed to evaluate if a particle trap on the tail pipe of an idling diesel engine would reduce effects on symptoms and lung function caused by the diesel exhaust, compared with exposure to unfiltered exhaust. METHODS: Twelve healthy non-smoking volunteers (aged 20-37) were investigated in an exposure chamber for one hour during light work on a bicycle ergometer at 75 W. Each subject underwent three separate double blind exposures in a randomised sequence: to air and to diesel exhaust with the particle trap at the tail pipe and to unfiltered diesel exhaust. Symptoms were recorded according to the Borg scale before, every 10 minutes during, and 30 minutes after the exposure. Lung function was measured with a computerised whole body plethysmograph. RESULTS: The ceramic wall flow particle trap reduced the number of particles by 46%, whereas other compounds were relatively constant. It was shown that the most prominent symptoms during exposure to diesel exhaust were irritation of the eyes and nose and an unpleasant smell increasing during exposure. Both airway resistance (R(aw)) and specific airway resistance (SR(aw)) increased significantly during the exposures to diesel exhaust. Despite the 46% reduction in particle numbers by the trap effects on symptoms and lung function were not significantly attenuated. CONCLUSION: Exposure to diesel exhaust caused symptoms and bronchoconstriction which were not significantly reduced by a particle trap.

The Effect of Fuel and Engine Design on Diesel Exhaust Particle Size Distributions

Abstract: The objective of this research was to obtain diesel particle size distributions from a 1988 and a 1991 diesel engine using three different fuels and two exhaust control technologies (a ceramic particle trap and an oxidation catalytic converter). The particle size distributions from both engines were used to develop models to estimate the composition of the individual size particles. Nucleation theory of the H{sub 2}O and H{sub 2}SO{sub 4} vapor is used to predict when nuclei-mode particles will form in the dilution tunnel. Combining the theory with the experimental data, the conditions necessary in the dilution tunnel for particle formation are predicted. The paper also contains a discussion on the differences between the 1988 and 1991 engine`s particle size distributions. The results indicated that nuclei mode particles (0.0075--0.046 {micro}m) are formed in the dilution tunnel and consist of more than 80% H{sub 2}O-H{sub 2}SO{sub 4} particles when using the 1988 engine and 0.29 wt% sulfur fuel. Nucleation theory indicated that H{sub 2}O-H{sub 2}SO{sub 4} particles may form during dilution at 0.03 wt% fuel sulfur levels and above. The 1991 engine was designed for lower particulate emissions than the 1988 engine and the 1991 engine`s accumulation mode particles (0.046-1.0 {micro}m) weremore » reduced more than 80% by volume compared to the 1988 engine using the same low sulfur fuel. The particle size composition model indicated that using low sulfur fuel and the 1991 engine, the nuclei mode contained more than 45% of the total solid particles and over 85% of the soluble organic fraction.« less

Method for purifying exhaust gas of a diesel engine

Abstract: According to the method of the present invention, NO (nitrogen monoxide) in the exhaust gas of a diesel engine is first oxidized to NO 2 (nitrogen dioxide) by an oxidizing catalyst. Further, carbon particles in the exhaust gas are trapped by a DPF (diesel particulate filter). The exhaust gas containing NO 2 formed by oxidation of nitrogen monoxide is, then, fed to the DPF, and NO 2 in the exhaust gas reacts with the carbon particles trapped in the DPF. When the NO 2 reacts with carbon particles, carbon particles are oxidized (burned) by NO 2 and removed from DPF, and, at the same time, NO 2 is reduced to NO by the carbon particles. The exhaust gas containing NO formed by the reaction between the carbon particles and NO 2 is fed to an NO X absorbent. In the NO X absorbent, NO is absorbed by the NO X absorbent and, thereby, removed from the exhaust gas. Therefore, according this method, the carbon particles collected by the DPF can be easily burned by NO 2 , thereby being removed from the DPF without increasing the amount of NO released to the atmosphere.

Monolithic diesel oxidation catalysts

Abstract: A flow-through ceramic monolithic catalyst, containing bulk CeO 2 as the catalytically active component, is reported for the catalytic oxidation of the liquid portion of the particulates present in diesel engine exhausts. This new technology has been successfully implemented into medium duty trucks in the U.S. beginning in 1994 meeting all required emission standards. Catalyst screening and engine durability/aging results and a proposed mechanism of operation are presented. The addition of a proprietary zeolite as a hydrocarbon trap and a small amount of Pt to the platform CeO 2 catalyst enables european emission standards for CO, HC and particulates to be met. Commercialization of this technology in Europe began in the first part of 1996.

Combustion Analysis of Esters of Soybean Oil in a Diesel Engine

Abstract: The alkyl esters of plant oils and animal fats are receiving increasing attention as renewable fuels for diesel engines. These esters have come to be known as biodiesel. One objection to the use of the methyl and ethyl esters of soybean oil as a fuel in diesel engines is their high crystallization temperature. One solution to this problem is to use the isopropyl esters of soybean oil which have significantly lower crystallization temperatures. Another method to improve the cold flow properties of esters is to winterize them to subambient temperature. This is accomplished by cooling the esters and filtering out the components that crystallize most readily. Previous work has shown that when methyl, isopropyl and winterized ester blends were compared with No. 2 diesel fuel, the isopropyl and winterized methyl esters had at least the same emission reduction potential as the methyl esters, with similar engine performance. This paper discusses those results using heat release analysis that shows all of the blends have shorter ignition delays, and lower premixed burn fractions than No. 2 diesel fuel. All tested fuels except the isopropyl ester blends had similar combustion behavior. However, blends with isopropyl ester showed some abnormal combustion behavior, possibly duemore » to high levels of monoglycerides.« less

Worldwide diesel emission standards, current experiences and future needs

Abstract: The tightening of future exhaust emission limits for diesel engines and diesel vehicles require more and more extraordinary development efforts with respect to reducing both engine-out emissions by improved combustion processes and tailpipe emissions by new exhaust gas aftertreatment systems (EGAS). Today, the main EGAS activities in engine application as well as in research and development concentrates on oxidation catalysts, particulate traps, and DENOX catalysts. This paper deals with 1. a general overview on the development directions of different EGAS and typical emission reduction examples for various diesel engine and vehicle applications; 2. the interaction between legislative emission test cycles, combustion system development and the kind of EGAS used. Based on current development work and test results, ranking considerations with regard to the application and development probability of EGAS are given.

Device for purifying the exhaust gas of a diesel engine

Abstract: A device for purifying the exhaust gas of a diesel engine comprises a filter for collecting particulates which is arranged in the exhaust system of the engine, an oxidation catalyst arranged in the exhaust system upstream of the filter, diesel fuel supply unit for supplying diesel fuel to the oxidation catalyst when the filter must be regenerated, and a heater. The heater heats the diesel fuel supplied from the diesel fuel supply unit to the oxidation catalyst only in the initial step of supplying the diesel fuel when the temperature of the oxidation catalyst is lower than a predetermined temperature and the filter must be regenerated.

The dilution, chemical, and thermal effects of exhaust gas recirculation on diesel engine emissions-part 2: Effects of carbon dioxide

Abstract: This is the second of a series of papers on how exhaust gas recirculation (EGR) affects diesel engine combustion and emissions. It concentrates on the effects of carbon dioxide (CO2) which is a principal constituent of EGR. Results are presented from a number of tests during which the nitrogen or oxygen in the engine inlet air was progressively replaced by CO2 and/or inert gases, whilst the engine speed, fuelling rate, injection timing, inlet charge total mass rate and inlet charge temperature were kept constant. In one set of tests, some of the nitrogen in the inlet air was progressively replaced by a carefully controlled mixture of CO2 and argon. This ensured that the added gas mixture had equal specific heat capacity to that of the nitrogen being replaced. Thus, the effects of dissociated CO2 on combustion and emissions could be isolated and quantified (chemical effect). In another set of tests, some of the nitrogen in the inlet air was progressively replaced by a carefully controlled mixture of helium and nitrogen. This ensured that the mixture replacing the nitrogen in the air had a specific heat capacity equal to that of CO2. Thus the effects of the high heat absorbing capacity of CO2 on combustion and emissions could be isolated and quantified (thermal effect). In a final series of tests some of the oxygen in the inlet air was progressively replaced by CO2 in order to quantify the overall effects of CO2 on combustion and emissions and compare with the individual chemical, thermal, and dilution effects. It was found that CO2 dissociation had small but measurable effects on exhaust emissions. The high heat absorbing capacity of CO2 had only a small effect on exhaust emissions (including NOx); this finding challenges conventional wisdom as to the importance of the higher heat capacity of CO 2 in suppressing NOx when EGR is added to the inlet air of diesel engines. © 1996 Society of Automotive Engineers, Inc.

Method and apparatus for operating a diesel engine

Abstract: A method and an apparatus are provided for operating a diesel engine with an exhaust feedback device located between the exhaust line and the intake air line, with an adjusting element that can be operated by an adjusting drive actuated by an auxiliary force to operate the exhaust feedback device as a function of signals from an electronic control device. An engine regulator permits rich/lean regulation of the diesel engine as a function of its operating parameters. A storage catalyst is located in the exhaust line, in which catalyst oxides of nitrogen (NO x ) can be adsorbed, desorbed, and reduced. A sensor is located downstream from the storage catalyst for detecting the NO x concentration in the exhaust stream in such fashion that when an NO x storage threshold value is reached that varies in terms of its characteristics as a function of the rpm and the load, a switch is made from operation with a lambda value of larger than 1 to operation with a lambda value of less than 1.

Exhaust emission control apparatus for internal combustion engine

Abstract: To accomplish an optimum regeneration operation of an exhaust emission control apparatus (124), the quantity of nitrogen oxide (C) absorbed in catalysts (125, 812) and an exhaust gas temperature (T) are predicted on the basis of future driving condition information obtained from a car navigation system (141, 841), etc., and an appropriate time for regeneration is determined at which the absorption quantity of the catalysts (125, 812) is expected to be large and the exhaust gas temperature (T) is expected to be in a predetermined temperature range. When the time for regeneration is reached, the exhaust gas is made rich and the nitrogen oxides are emitted from the catalyst (125, 812) to regenerate the catalyst. The nitrogen oxides emitted from the catalyst (125, 812) are reduced to innoxious substances by unburnt hydrocarbons in the exhaust gas, etc. When this apparatus is applied to a particulate filter (814) of a diesel engine, the chance of operation for raising the exhaust gas temperature (T) decreases, so that deterioration of the fuel cost can be restricted.

A method for purifying exhaust gas of a diesel engine

Abstract: According to the method of the present invention, NO (nitrogen monoxide) in the exhaust gas of a diesel engine is first oxidized to NO2 (nitrogen dioxide) by an oxidizing catalyst (5). Further, carbon particles in the exhaust gas are trapped by a DPF (7) (diesel particulate filter). The exhaust gas containing NO2 formed by oxidation of nitrogen monoxide is, then, fed to the DPF (7), and NO2 in the exhaust gas reacts with the carbon particles trapped in the DPF (7). When the NO2 reacts with carbon particles, carbon particles are oxidized (burned) by NO2 and removed from DPF (7), and, at the same time, NO2 is reduced to NO by the carbon particles. The exhaust gas containing NO formed by the reaction between the carbon particles and NO2 is fed to an NOX absorbent (9). In the NOX absorbent (9), NO is absorbed by the NOX absorbent (9) and, thereby, removed from the exhaust gas. Therefore, according this method, the carbon particles collected by the DPF (7) can be easily burned by NO2, thereby being removed from the DPF (7) without increasing the amount of NO released to the atmosphere.

Simultaneous control of particulate and NOx emissions from diesel engines

Abstract: In view of increased concerns regarding the effects of diesel engine particulate and NO x emissions on human health and the environment, legislators are currently reviewing and proposing legislation targeting the reduction of these pollutants. The reported serious health risks of particulate matter on the respiratory system and its carcinogenic effects, along with the known contributions of NO x in acid rain and ground ozone formation, demand that the enacted legislation reflect in severity the health and environmental threats. As a consequence, diesel engine manufacturers and users are under increasing pressure to greatly reduce the engine's exhaust emissions. A system which is currently being proposed for the simultaneous control of diesel particulate matter and NO x emissions involves the use of a cerium fuel-borne catalyst/filter/EGR system. This paper describes the principles of operation of Rhoˆne-Poulenc's cerium fuel-borne catalyst and the factors that govern its use.

Methods for reducing harmful emissions from a diesel engine

Abstract: Emissions of pollutants from diesel engines are reduced by a combination of mechanical devices and fuel additives. In one series of embodiments, diesel emissions of NOx and particulates are reduced, simultaneously with gaseous hydrocarbons and carbon monoxide, by the combined use of exhaust gas recirculation or engine timing modification, with a particulate trap and a platinum group metal catalyst composition. In another embodiment, a multi-metal catalyst composition, comprising a combination of a platinum metal catalyst composition and at least one auxiliary catalyst metal composition, especially cerium or copper, is employed to provide catalyst metal to the exhaust system including a diesel trap to lower the balance point of the particulate trap (the temperature at which the rate of trap loading equals the rate of regeneration) while also lowering the emissions of carbon monoxide and unburned hydrocarbons. Data for platinum, copper and cerium catalysts establishes effective amounts. Tests also show selective maintenance of low oxidation of SO2 to SO3.

EGR and blow-by flow system for highly turbocharged diesel engines

Abstract: A gas flow network in combination with a highly turbocharged diesel engine for the blending of either EGR gas or blow-by gas from the crankcase vent with fresh charge air is disclosed. In the diesel engine assembly which incorporates the flow network for EGR gas, a venturi conduit and control valve combination is positioned between tile intake manifold and aftercooler and is connected to a flow line carrying the EGR gas. When the turbocharged diesel engine assembly is configured with a flow path for blow-by gas, the venturi and control valve combination is positioned between the intake manifold and aftercooler and is connected to a flow line carrying blow-by gas. These systems utilize a low static pressure at the narrow throat of the venturi so as to induce the flow of EGR gas or blow-by gas into the fresh charge air, the flow being controlled by the state of the control valve.

Integrated fuel injector and ignitor assembly

Abstract: An integrated fuel injector and ignitor assembly is provided which includes an injector body, a fuel control valve and an ignition device. The components are packaged to create a compact assembly for positioning within an injector mounting bore and particularly in a mounting bore of an existing diesel engine. The assembly may include a fuel reservoir for accumulating fuel for injection so as to stabilize the injection pressure. Also, the ignition device may include an ignition coil mounted on the injector body and a replaceable ignitor electrode cartridge mounted on an opposite end of the injector body to permit simple, cost effective replacement of the electrodes/spark plug.

Accumulator fuel injection device

Abstract: In an accumulator fuel injection device pulsating of pressure is suppressed and fluctuation of fuel injection is prevented by providing flow rate control means such as an orifice generating a flow rate regulated at a fuel passage of a diesel engine. The device supplies fuel to injectors of cylinders from a pump pressurizing the fuel to a high pressure through a common rail which can stock high pressure fuel or through a corresponding fuel passage having a large volume.

Burner for the thermal regeneration of a particle filter in an exhaust gas aftertreatment system of an internal combustion engine, especially a diesel engine

Abstract: Four design variants of a full-flow burner for the thermal regeneration of a particle filter in an exhaust gas aftertreatment system of an internal combustion engine, especially a diesel engine, which is arranged fully in the tailpipe, especially in an expanded, straight coaxial tailpipe section, are suggested according to the present invention. As a result, the flow can enter a particle filter axially, which means simplified design and good temperature distribution. The full-flow burners are preheated by the heat of the exhaust gas of the engine during the start phase. The exhaust gas of the engine cools the burner surface during the phase of burner operation, so that thermal overload is avoided.

The Dilution, Chemical, and Thermal Effects of Exhaust Gas Recirculation on Diesel Engine Emissions - Part 3: Effects of Water Vapour

Abstract: Water vapour is a main constituent of exhaust gas recirculation (EGR) in diesel engines and its influence on combustion and emissions were investigated The following effects of the water vapour were examined experimentally: the effect of replacing part of the inlet charge oxygen (dilution effect), the effect of the higher specific heat capacity of water vapour in comparison with that of oxygen it replaces (thermal effect), the effect of dissociation of water vapour (chemical effect), as well as the overall effect of water vapour on combustion and emissions Water vapour was introduced into the inlet charge, progressively, so that up to 3 percent of the inlet charge mass was displaced This was equivalent to the amount of water vapour contained in 52 percent by mass of EGR for the engine operating condition tested in this work The introduction of water vapour in the inlet charge resulted in a slight increase in the ignition delay, and a slight decrease in the peak cylinder gas pressure and temperature The reduction in NOx emissions was mainly due to the dilution of the inlet charge with water vapour while the higher specific heat capacity had a considerable effect too The separate effects of water vapour on the unburnt hydrocarbon emissions (UHC) were minor, whereas the overall effect was relatively substantial The introduction of water vapour resulted in an increase in the particulate and smoke emissions Part of this increase was due to the dilution effect of the inlet charge with water vapour The algebraic addition of the dilution, the chemical, and the thermal effects on the UHC and the volatile fraction of the particulates was not equal to the overall effect of water vapour This indicated that there might be an additional (but not identified) effect that increased the volatile organic fraction as well as the UHC emissions Alternatively, it is suggested that the sum of the separate dilution, chemical, and thermal effects of water vapour on, for example, ignition delay and, thereby, emissions may be different from that of the overall effect of water vapour on ignition delay and emissions This is the third paper in a series which deals with the effects of EGR on combustion and emissions in diesel engines The first and second papers are SAE 961165 and SAE 961167, respectively © 1997 Society of Automotive Engineers, Inc

The Effect of Exhaust Gas Recirculation on Combustion and NOx Emissions in a High-Speed Direct-injection Diesel Engine

Abstract: A number of tests were conducted on a 2.5 litre, high-speed, direct-injection diesel engine running at various loads and speeds. The aim of the tests was to gain understanding which would lead to more effective use of exhaust gas recirculation (EGR) for controlling exhaust NOx. In addition to exhaust emission measurements, extensive in-cylinder sampling of combustion gases was carried out using a fast-acting, snatch-sampling valve. The results showed that the effectiveness of EGR in suppressing NOxwas enhanced considerably by intercooling the inlet charge and by cooling the EGR. A companion paper (SAE 960841) deals with the effects of EGR on soot formation and emission [1]. © Copyright 1996 Society of Automotive Engineers, Inc.

The Effect of Exhaust Gas Recirculation on Soot Formation in a High-Speed Direct-injection Diesel Engine

Abstract: A number of tests were conducted on a 2.5 litre, high-speed, direct-injection diesel engine running at various loads and speeds. The aim of the tests was to gain understanding which would lead to more effective use of exhaust gas recirculation (EGR) for controlling exhaust NOx whilst minimising the penalties of increased smoke emission and fuel consumption. In addition to exhaust emission measurements, in-cylinder sampling of combustion gases was carried out using a fast-acting, snatch-sampling valve. The results showed that the effectiveness of EGR was enhanced considerably by cooling the EGR. In addition to more effective NOx control, this measure also improved volumetric efficiency which assisted in the control of smoke emission and fuel consumption. This second of two papers on the use of EGR in diesel engines deals with the effects of EGR on soot emission and on the engine fuel economy. This paper should be read in conjunction with the first paper (SAE 960840) which deals with formation and control of NOx, and which contains more background information on the use of EGR in diesel engines and on the tests conducted [1]. © Copyright 1996 Society of Automotive Engineers, Inc.