Search Results

Close coupled catalysts represent a solution being pursued by automotive engineers to meet stringent LEV and ULEV emission standards. Close coupled systems provide fast light-off by utilizing the energy in the exhaust gas rather than energy supplied by an auxiliary source such as an electrically heated catalyst or a burner in the exhaust. Previous close coupled catalyst designs were limited by the temperature capability of the catalyst coatings. A successful close coupled catalyst technology has been developed 'that is resistant to higher temperature deactivation. This technology is able to function well at low temperature during the vehicle cold start when light-off is critical. The close coupled catalyst technology has approached ULEV emission levels after aging at 1050°C for 24 hours. This study will present experimental results for a close coupled catalyst including the selection of catalyst volume, cross sectional area and combination of catalyst technologies.

This paper consists of two parts. Part I concerns the effects of injection timing, injection rate, and air swirl on emission of smoke and gaseous pollutants from direct-injection diesel engines. Studies show that fuel-injection equipment and variables such as nozzle configuration affect pollutant production and emission because they affect fuel-air mixing. An increased rate of injection or air swirl increases the rate of fuel-air mixing and reduces the amount of exhaust smoke and its dependence on injection timing. An increase in rate or swirl ratio increases nitric oxide emission at a given injection timing, but the increase is relatively small compared with reduction obtained by retarding injection timing. Substantial retard, in conjunction with increased rate of fuel-air mixing, limits loss in engine efficiency. Part II reports development of a model for calculating soot and nitric oxide formation.

Fuels of widely varying properties are studied by injection of a single and well defined spray into an experimental diesel engine. Three optical techniques were developed to visualise liquid fuel, fuel vapour, flame, soot and individual droplets and their associated vapour trails. Liquid core length measurements are presented for diesel fuel, toluene, ethanol and sunflower oil. Computer model predictions show that an increase of the fuel mid-boiling point by 40°C gives a similar effect on liquid core length to an increase of 0.03mm in the nozzle hole diameter.

Close-coupled catalysts are being actively pursued by automotive engineers in order to meet stringent LEV/ULEV emission standards. However, future applications of close coupled catalyst will be exposed to 50 to 100°C higher operating temperatures with elimination of fuel enrichment to cool the catalyst. A successful close coupled catalyst technology must then be resistant to even higher temperature deactivation and yet continue to function at low temperature during the vehicle cold start. A close coupled catalyst technology is formulated through advanced catalyst design to meet LEV and ULEV emission standards after high temperature aging at 1050°C. This paper will show the inherent stability of the close coupled catalyst for both light-off temperature and steady state performance for aging temperatures up to 1100°C.

A numerical study has been performed to investigate the soot emission from a high-speed single-cylinder direct injection diesel engine. It was shown that the current KIVA CFD code with the standard evaporation model could predict the experimental trend, where at a low speed running condition a higher smoke reading is reached when increasing the injector protrusion into the piston chamber and conversely a lower smoke reading was recorded for the same change in injector protrusion at a high running speed condition. Evidence of inappropriate air/fuel mixing was seen via rates of heat release analyses, especially in the high-speed conditions. Efforts to reduce this discrepancy by way of improvements to the KIVA breakup and evaporation models were made. Results of the modified models showed improvements in the vapor dispersion of the atomizing liquid jet, thus affecting the mixing rates and predicted smoke emissions.

An experimental study has been carried out on a single-cylinder pressure-charged engine with a near quiescent combustion system. An improvement in the NOx/BSFC trade-off was achieved by two different approaches, namely exhaust gas recirculation and pilot injection. Without EGR, a reference EUI-200 system with 1900 bar peak injection pressure gave a low soot particulate level of 0.013 g/bhp h over a simulation of the US FTP cycle. The results with EGR show how higher levels of EGR can be used at more advanced injection timings to give substantially improved NOx versus BSFC results compared with timing retard alone. It was possible to reduce the NOx from 4.85 to 3.6 g/bhp h for no increase in BSFC over the simulated US FTP cycle and with a total calculated particulate of 0.075 g/bhph. The results with electronically-controlled pilot injection show improvements in NOx versus BSFC, lower NOx before HC increase with retard, or reduced combustion noise at certain test modes.

An analytical technique has been optimised for the measurement of the concentrations of diesel exhaust odorants. Application of this technique to combustion bomb studies shows that preflame reactions with diesel fuel produce high concentrations of odorants. The effects of engine variables on exhaust odorant concentrations are presented for direct and indirect injection engines. Analysis of these data shows that diesel exhaust odorants are produced from three sources: (a) the fuel-lean mixture produced during the ignition delay period, (b) fuel emptying from the nozzle sac volume of direct injection engines after injection, (c) a fuel-rich source which becomes significant at high load. The practical measures for control of odorants are outlined.

For many years, compression ignition combustion has been studied by a combination of generic studies on fuel spray formation and analysis of results from single and multicylinder engines. The results and insight have been applied to design and develop advanced fuel injection equipment for high-speed direct injection engines. Experimental fuel injection equipments, including early common rail designs, have been matched to combustion chambers in single cylinder research engines to tackle the conflicting requirements of efficiency and minimum nitric oxide formation, combustion noise and soot. A clear strategy evolved from the work with experimental equipment that is being applied to multicylinder engines. If sufficient oxygen is available in the gas charge trapped in each cylinder, the LDCR common rail injection system will provide the fuel required to develop high torque at low engine speeds.

Emissions results are presented from an experimental study of an indirect injection diesel engine. The mass measurements of particulate emission are correlated with the measurements of smoke and HC emission. The correlation provides a less expensive way of carrying out preliminary combustion optimisation work. It is concluded that practically all of the particulate mass emission is accounted for by: (a) the black smoke or soot formed in the high temperature fuel-rich regions of the diffusion phase of burning, (b) that fraction (about 50%) of the total HC mass emission which condenses at the particulate sampling filter. The total HC mass emission is itself a function of three distinct sources in the combustion process. The understanding gained is then used to define three combustion ideals for optimising diesel combustion to minimise fuel consumption and emissions of smoke, NOX, particulates, HC, CO, odor and noise.

Experimental data on the concentration of hydrocarbons (HC) emitted in the exhaust are presented for both direct injection (DI) and indirect injection (IDI) engines and cover the effect of a wide range of engine operating parameters. The analysis shows that there are two main sources of HC in DI engines. One is due to the volume of fuel in the sac and holes of the injection nozzle and the other is from fuel premixed to leaner than lean limit conditions. Reduction of sac volume and reduction of ignition delay are effective in reducing the HC from the sac volume and lean limit sources respectively. Developments in fuel injection equipment and engine design to reduce HC emissions are outlined.

The paper considers the combustion regimes which lead to the emission of HC and CO in diesel combustion systems. Experimental data are presented to show the effect of a wide range of operating variables on the emission of HC and CO from a range of production automotive diesel engines. Analysis of the data shows that three localised sources account for most of the HC and CO emissions. The measures required to exploit the very low emissions potential of the diesel engine are discussed.

The purpose of the European « SPACE LIGHT » (Whole SPACE combustion for LIGHT duty diesel vehicles) 3-year project launched in 2001 is to research and develop an innovative Homogeneous internal mixture Charged Compression Ignition (HCCI) for passenger cars diesel engine where the combustion process can take place simultaneously in the whole SPACE of the combustion chamber while providing almost no NOx and particulates emissions. This paper presents the whole project with the main R&D tasks necessary to comply with the industrial and technical objectives of the project. The research approach adopted is briefly described. It is then followed by a detailed description of the most recent progress achieved during the tasks recently undertaken. The methodology adopted starts from the research study of the in-cylinder combustion specifications necessary to achieve HCCI combustion from experimental single cylinder engines testing in premixed charged conditions.

The purpose of the ELEVATE (European Low Emission V4 Automotive Two-stroke Engine) industrial research project is to develop a small, compact, light weight, high torque and highly efficient clean gasoline 2-stroke engine of 120 kW which could industrially replace the relatively big existing automotive spark ignition or diesel 4-stroke engine used in the top of the mid size or in the large size vehicles, including the minivan vehicles used for multi people and family transportation. This new gasoline direct injection engine concept is based on the combined implementation on a 4-stroke bottom end of several 2-stroke engine innovative technologies such as the IAPAC compressed air assisted direct fuel injection, the CAI (Controlled Auto-Ignition) combustion process, the D2SC (Dual Delivery Screw SuperCharger) for both low pressure engine scavenging and higher pressure IAPAC air assisted DI and the ETV (Exhaust charge Trapping Valve).

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 (CO2) 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.

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).

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.

This paper deals with the effects on diesel engine combustion and emissions of carbon dioxide and water vapour the two main constituents of EGR. It concludes the work covered in Parts 1, 2, and 3 of this series of papers. A comparison is presented of the different effects that each of these constituents has on combustion and emissions. The comparison showed that the dilution effect was the most significant one. Furthermore, the dilution effect for carbon dioxide is higher than that for water vapour because EGR has roughly twice as much carbon dioxide than water vapour. On the other hand, the water vapour had a higher thermal effect in comparison to that of carbon dioxide due to the higher specific heat capacity of water vapour. The chemical effect of carbon dioxide was, generally, higher than that of water vapour.

This paper is a complementary to previous investigations by the authors (1,2,3,4) on the different effects of EGR on combustion and emissions in DI diesel engine. In addition to the several effects that cold EGR has on combustion and emissions the application of hot EGR results in increasing the inlet charge temperature, thereby, for naturally aspirated engines, lowering the inlet charge mass due to thermal throttling. An associated consequence of thermal throttling is the reduction in the amount of oxygen in the inlet charge. Uncooled EGR, therefore, affects combustion and emissions in two ways: through the reduction in the inlet charge mass and through the increase in inlet charge temperature. The effect on combustion and emissions of increasing the inlet charge temperature (without reducing the inlet charge mass) has been dealt with in ref. (1).