Energy conservation and the United Kingdom engineering industry

Imperial Users onl

The effect of piston bowl temperature on diesel exhaust emissions

In modern, high-speed, direct injection diesel engines for passenger vehicles, there is extensive impingement of the fuel sprays on to the piston bowl walls. Recent trends towards smaller engine sizes, equipped with high-pressure common-rail fuel injection systems, have tended to increase the spray/piston wall interaction. This paper describes tests carried out in a high-speed direct injection automotive diesel engine, during which the temperature of the piston was increased in a controlled manner between 189 and 227 degrees C while being continuously monitored. The aim of the work was to quantify the effects of piston temperature on pollutant exhaust emissions. The results show a significant reduction in unburned hydrocarbon emission, a significant increase in smoke emission, and no significant change in the emission of oxides of nitrogen. The increase in smoke emission cannot be ascribed to changes in the engine volumetric efficiency or air-fuel ratio. The paper demonstrates that fuel spray deposition on the piston surface was in the form of a thin film that did not experience bulk boiling. A number of suggestions are put forward to help explain the observed changes in exhaust emissions with increasing piston temperature

Characteristics of homogeneous charge compression ignition (HCCI) combustion and emissions of n-heptane

This paper reports the outcome from a systematic investigation carried out on HCCI (Homogeneous Charge Compression Ignition) combustion of a diesel type fuel. The n heptane was chosen in this study to study the premixed diesel HCCI combustion characteristics with port fuel injection. Measurements were carried out in a single-cylinder, 4-stroke and variable compression ratio engine. Premixed n-heptane/air/EGR mixture was introduced into the cylinder by a port fuel injector and an external EGR system. The operating regions with regard to Air/Fuel ratio and EGR rate were established for different compression ratios and intake temperatures. The effects of compression ratios, intake temperatures, Air/Fuel ratios and EGR rates on knock limit, auto-ignition timing, combustion rate, IMEP, and engine-out emissions, such as NOx, CO, and unburned HC, were analysed. The results have shown HCCI combustion of n-heptane could be implemented without intake charge heating with a typical diesel engine compression ratio. The attainable HCCI operating region was mainly limited by the knock limit, misfir, and low IMEP respectively. Higher intake temperature or compression ratio could extend the misfire limit of the HCCI operation at low load but they would reduce the maximum IMEP limit at higher load conditions. Compared with conventional diesel combustion, HCCI combustion lead to extremely low NOx emissions ( less than 5 ppm) and smoke free exhaust. But HCCI diesel combustion was found to produce higher HC and CO emissions. An increase in intake temperature or compression ratio helped to reduce HC and CO emissions.

Visualization of the homogeneous charge compression ignition/controlled autoignition combustion process using two-dimensional planar laser-induced fluorescence imaging of formaldehyde

The paper reports an investigation into the HCCI/CAI combustion process using the two-dimensional PLIF technique. The PLIF of formaldehyde formed during the low-temperature reactions of HCCI/CAI combustion was exciting by a tunable dye laser at 355nm wavelength and detected by a gated ICCD camera. Times and locations of the two-stage autoignition of HCCI/CAI combustion were observed in a single cylinder optical engine for several fuel blends mixed with n-heptane and iso-octane. The results show, when pure n-heptane was used, the initial formation of formaldehyde and its subsequent burning were closely related to the start of the low temperature heat release stage and the start of the main heat release stage of HCCI combustion respectively. Meanwhile, it was found that the formation of formaldehyde was more affected by the charge temperature than by the fuel concentration. But its subsequent burning or the start of main heat release combustion toke place at those areas where both the fuel concentration and the charge temperature were sufficient high. As a result, it was found that the presence of stratified residual gases affected both the spatial location and the temporal site of autoignition in a HCCI/CAI combustion engine. All studied fuels were found having similar formaldehyde formation timings with n-heptane. This means that the presence of iso-octane did not affect the start of low temperature reactions apparently. However, the heat release during low temperature reaction was significantly reduced with the presence of iso-octane in the studied fuels. In addition, the presence of iso-octane retarded the start of the main combustion stage

An investigation into the conversion of specific carbon atoms in oleic acid and methyl oleate to particulate matter in a diesel engine and tube reactor

The paper is concerned with particulate formation from the fuels oleic acid and methyl oleate. In particular the paper reports, quantitatively, the propensity of individual carbon atoms in these two molecules in being converted to particulate. The conversion of individual carbon atoms to particulate was traced by 'labelling' individual carbon atoms in those two fuel molecules with isotopic carbon-13 (C) and then measuring how many of the labelled atoms was found in the particulate. This allowed the measuring of the conversion rates of individual fuel carbon atoms to particulate. In the case of oleic acid, three carbon atoms were selected as being particularly relevant to particulate formation, and C labelled. One of the carbon atoms was double bonded to the oxygen atom on the carboxylic acid group; and the other two were part of the oleic acid molecule alkyl chain and double bonded to each other. In the case of the methyl oleate, one carbon atom was C labelled. This was the carbon atom that was double bonded to one of the oxygen atoms of the ester group. Experimental results are presented for particulate matter (PM) formed in a laminar flow tube reactor, and also in a direct injection compression ignition engine. The tube reactor has been used for the pyrolysis of oleic acid and methyl oleate at 1300 °C, under oxygen-free conditions and at air-fuel equivalence ratios (λ) of 0.1, and 0.2. Samples of PM were also collected from the compression ignition engine at an intermediate engine load. Isotope ratio mass spectrometry (IRMS) has been used to determine the relative abundance of C in the initial fuel and in the resulting PM. Significant differences in the relative conversion rates of individual carbon atoms are reported; a negligible contribution to PM from the carbon atom directly bonded to two oxygen atoms was found in both the engine and reactor. The labelling technique used in this paper requires low quantities of C labelled molecules to enrich otherwise unlabelled oleic acid; enrichment is at volumetric concentrations typically less than 0.7% (v/v). In addition, emissions data from the engine and tube reactor, including unburned hydrocarbons, CO, CO, NO, and PM size and number distributions measured by differential mobility spectrometer, are also presented

Investigations on Deposit Formation in the Holes of Diesel Injector Nozzles

Current developments in fuels and emissions regulations are resulting in an increasingly severe operating environment for diesel fuel injection systems. The formation of deposits within the holes or on the outside of the injector nozzle can affect the overall system performance. The rate of deposit formation is affected by a number of parameters, including operating conditions and fuel composition. For the work reported here an accelerated test procedure was developed to evaluate the relative importance of some of these parameters in a high pressure common rail fuel injection system. The resulting methodology produced measurable deposits in a custom made injector nozzle on a single cylinder engine. The results indicate that fuels containing 30%v/v and 100% Fatty Acid Methyl Ester (FAME), that does not meet EN 14214 produced more deposit than an EN590 petroleum diesel fuel. Overall, the addition of zinc to the fuel had the biggest effect on deposit formation and resulted in a 12.2% decrease in Indicated Mean Effective Pressure (IMEP). The effects of zinc were unexpectedly reduced when it was added to fuel containing 30%v/v biodiesel. Reducing the common-rail pressure with 30%v/v biodiesel (no added zinc) increased the loss in IMEP. Raising the air and fuel temperatures by 40°C and 30°C respectively showed no bigger loss in IMEP. The results indicate that deposit formation may continue after engine shut down. © 2011 Society of Automotive Engineers of Japan, Inc. and SAE International

The effect of varying EGR and intake air boost on hydrogen-diesel co-combustion in CI engines

This paper presents a H2-diesel fuel co-combustion study undertaken on a supercharged, direct injection, diesel engine investigating the combustion characteristics and emissions production at a range of engine loads (IMEP), EGR levels and intake air boosting conditions. The utilisation of EGR and intake air boost with H2-diesel fuel co-combustion allows simultaneous NOx and particulate emissions reduction at conditions closer to on-road driving conditions.The results showed that while H2 can be favourable in reducing CO2 and particulate emissions, it causes an increase in NOx emissions when the intake energy contribution from H2 is increased. A reduction in the number of fine and ultrafine particles (diameter 0.05-0.2 μm) was observed when H2 was added to the engine, especially at the low and intermediate intake air boost levels. At high EGR levels (equivalent to 2% intake O2 concentration reduction) significant reductions in exhaust particulate mass of up to 75% were observed at 15% energy from H2. An attempt was made to identify the optimum H2 operating window at the different engine loads, intake air boost and EGR levels

Isotopic Tracers for Combustion Research

This review article deals with the use of isotopic tracers in the field of combustion science. A number of researchers have reported the use of isotopic techniques, which have been employed to solve a wide range of combustion problems. Radioactive and stable isotopes have been utilized as tracers, including isotopes of carbon (13C and 14C), oxygen (18O), and deuterium (D). One of the main applications has been to quantitatively determine the propensity of a molecule in a mixture, or specific atom within a molecule, to form pollutant emissions. Tracer studies have also been used for the elucidation of combustion reaction pathways, and kinetic rate constant determination of elementary reactions. A number of analytical techniques have been used for isotope detection; and the merits of some of the different techniques are discussed in the context of combustion research. This article concludes by exploring emerging methods and potential future techniques and applications

Combustion and exhaust emission characteristics, and in-cylinder gas composition, of hydrogen enriched biogas mixtures in a diesel engine

This paper presents a study undertaken on a naturally aspirated, direct injection diesel engine investigating the combustion and emission characteristics of CH4-CO2 and CH4-CO2-H2 mixtures. These aspirated gas mixtures were pilot-ignited by diesel fuel, while the engine load was varied between 0 and 7 bar IMEP by only adjusting the flow rate of the aspirated mixtures. The in-cylinder gas composition was also investigated when combusting CH4-CO2 and CH4-CO2-H2 mixtures at different engine loads, with in-cylinder samples collected using two different sampling arrangements. The results showed a longer ignition delay period and lower peak heat release rates when the proportion of CO2 was increased in the aspirated mixture. Exhaust CO2 emissions were observed to be higher for 60CH4:40CO2 mixture, but lower for the 80CH4:20CO2 mixture as compared to diesel fuel only combustion at all engine loads. Both exhaust and in-cylinder NOx levels were observed to decrease when the proportion of CO2 was increased; NOx levels increased when the proportion of H2 was increased in the aspirated mixture. In-cylinder NOx levels were observed to be higher in the region between the sprays as compared to within the spray core, attributable to higher gas temperatures reached, post ignition, in that region

Impact of increasing methyl branches in aromatic hydrocarbons on diesel engine combustion and emissions

Lignocellulosic materials have been identified as potential carbon–neutral sources of sustainable power production. Catalytic conversion of lignocellulosic biomass results in liquid fuels with a variety of aromatic molecules. This paper investigates the combustion characteristics and exhaust emissions of a series of alkylbenzenes, of varying number of methyl branches on the monocyclic aromatic ring, when combusted in a direct injection, single cylinder, compression-ignition engine. In addition, benzaldehyde (an aldehyde (-CHO) branch on the monocyclic ring) was also tested. All the molecules were blended with heptane in different proportions, up to 60% wt/wt. The tests were conducted at a constant engine speed of 1200 rpm, a fixed engine load 4 bar IMEP, and at two injection modes: constant start of fuel injection at 10 CAD BTDC, and varying fuel injection timing to maintain constant start of fuel combustion at TDC. The results showed that the ignition delay period increased with increasing number of methyl branches on the ring, due to the rapid consumption of OH radicals by the alkylbenzenes for oxidation to stable benzyl radicals. Peak heat release rates, and concurrently NOx emissions, initially increased with increasing methyl branches, but subsequently both decreased as the bulk of heat release occurred further into the expansion stroke with significant thermal energy losses. With the exception of toluene, the number of particles in the engine exhaust increased as the number of methyl branches on the aromatic ring increased, attributable to the formation of thermally stable benzyl radicals