Showing papers in "International Journal of Engine Research in 2009"

Review of diesel emissions and control

Abstract: This summary covers key and representative developments in diesel emissions regulations, engine developments, and nitrogen oxide (NOx), particulate matter (PM), and hydrocarbon (HC) remedia...

Effect of fuel cetane number on a premixed diesel combustion mode

Abstract: The ability of premixed low-temperature diesel combustion to deliver low particulate matter (PM) and NOx emissions is dependent on achieving optimal combustion phasing. Small deviations in combustion phasing can shift the combustion to less optimal modes, yielding increased emissions, increased noise, and poor stability. This paper demonstrates how variations in fuel cetane number affect the detailed combustion behaviour of a direct-injection, diesel-fuelled, premixed combustion mode. Testing was conducted under light load conditions on a modern single-cylinder engine, fuelled with a range of ultra-low sulphur fuels with cetane numbers ranging from 42 to 53. Fuel cetane number is found to affect ignition delay and, accordingly, combustion phasing. Gaseous emissions are a function of combustion phasing and exhaust gas recirculation (EGR) quantity, but are not directly tied to fuel cetane number. Fuel cetane number is merely one of many different engine parameters that shift combustion phasing. Furt...

Large eddy simulation modelling of spray-induced turbulence effects

Abstract: This study is focused on the development of spray models for large eddy simulations (LESs) of high injection pressure diesel sprays. Basic governing equations are numerically solved using the Lagrangian—Eulerian approach for liquid and gas phases respectively, in the KIVA-3V code. Non-reacting simulations of evaporating spray are performed using a dynamic structure LES model in which the subgrid stress tensor is modelled with a non-viscosity tensor coefficient. This is a one equation based model, in which an extra transport equation for the subgrid kinetic energy (k) is solved. Subgrid scale energy exchange between droplets and the gas phase is identified as an important mechanism to capture the correct scaling of k, which eventually feeds back to both the spray droplets and the gas phase turbulent mixing. Hence, to account for spray-induced gas turbulence, a LES spray source model for k is developed. This model requires subfilter scale velocities, which are obtained by defiltering the filtered ve...

Improvement of premixed charge compression ignition-based combustion by two-stage injection:

Abstract: The objective of this study is to find strategies for extending the load range of pre-mixed charge compression ignition-based combustion while improving thermal efficiency and reducing combustion noise and exhaust emission levels. Experiments were performed using a single-cylinder direct-injection diesel engine equipped with a common-rail injection system and a cooled EGR system. First, experiments were carried out with single-stage injection. The results indicated a notable improvement of NOx and smoke emissions by selecting lower EGR rates and later injection timings according to the increase in injection quantity. However, the problems of high pressure rise rates and levels of unburned species emissions developed. To solve these problems, two-stage injection was applied. These additional experimentsstarted with injection and EGR conditions that were based on the results of the single-stage injection tests, and modifications were made to mitigate the increased emissions and decreased thermal efficiency. As a result, judicious selection of injection and EGR conditions for two-stage injection provided a drastic improvement in exhaust emissions with a sufficiently low pressure rise rate to be equivalent to pilot-diesel operation.

Combustion in a heavy-duty direct-injection engine using hydrogen–methane blend fuels

Abstract: Adding hydrogen to the fuel in a direct injection natural gas engine offers the potential significantly to reduce local and global air pollutant emissions. This work reports on the effects of fuelling a heavy-duty engine with late-cycle direct injection of blended hydrogen—methane fuels and diesel pilot ignition over a range of engine operating conditions. The effect of hydrogen on the combustion event varies with operating condition, providing insight into the fundamental factors limiting the combustion process. Combustion stability is enhanced at all conditions studied; this leads directly to a significant reduction in emissions of combustion byproducts, including carbon monoxide, particulate matter, and unburned fuel. Carbon dioxide emissions are also significantly reduced by the lower carbon—energy ratio of the fuel. The results suggest that this technique can significantly reduce both local and global pollutant emissions associated with heavy-duty transport applications while requiring minima...

Understanding chemical effects in low-load-limit extension of homogeneous charge compression ignition engines via recompression reaction

Abstract: In-cylinder pre-processing (or recompression reaction) of pilot-injected fuel during negative value overlap (NVO) has been investigated as a method to extend the low-load limit of residual-effected homogeneous charge compression ignition (HCCI). In an effort to elucidate the chemical and thermal effects involved, model calculations have been performed on the recompression reaction and ignition delay of the recompression products using a reduced n-heptane mechanism (160 reactions, 1424 reactions) and a zero-dimensional kinetics model. Parametric studies were performed to cover possible operating choices for HCCI and to understand their effects on the recompression reaction and mixture ignitability. From the study it is demonstrated that the extent of recompression reaction is limited by chemical kinetics, not thermodynamics, and that residual oxygen during NVO is a determining species for the extent and speciation of the recompression reaction. The recompression product mixture exhibits an overall ...

Homogeneous charge compression ignition of hydrogen in a single-cylinder diesel engine

Abstract: Homogeneous charge compression ignition (HCCI) of hydrogen was studied using a single-zone model based in chemical reaction kinetics and using a single-cylinder Cooperative Fuels Research (CFR) diesel engine. Comparison was made with conventional diesel combustion at the same compression ratio and load. Simulation indicated that hydrogen HCCI should be feasible at compression ratios around 18 with intake heating to 100 °C, with peak efficiency occurring for moderately dilute equivalence ratios (0.2–0.5) with the minimum possible amount of intake heating. Experimental hydrogen HCCI was achieved with intake heating to 80 °C and 100 °C for equivalence ratios between 0.15 and 0.37. Hydrogen HCCI exhibited unburned hydrogen emissions of the order of 0.5–1.0 per cent, corresponding to combustion efficiencies of 90–95 per cent. Emissions of nitric oxides were typically below 1 ppm and were at least two orders of magnitude lower than a comparable diesel cycle. Efficiency of hydrogen HCCI was lower than a ...

Impact of filtration velocities and particulate matter characteristics on diesel particulate filter wall loading

Abstract: The impact of different types of diesel particulate matter (PM) and different sampling conditions on the wall deposition and early soot cake build up within diesel particulate filters has been investigated. The measurements were made possible by a newly developed Diesel Exhaust Filtration Analysis (DEFA) system in which in-situ diesel exhaust filtration can be reproduced with in small cordierite wafer disks, which are essentially thin sections of a Diesel Particulate Filter (DPF) wall. The different types of PM were generated from selected engine operating conditions of a single-cylinder heavy-duty diesel engine. Two filtration velocities 4 and 8 cm/s were used to investigate PM deep-bed filtration processes. The loaded wafers were then analyzed in a thermal mass analyzer that measures the Soluble Organic Fraction (SOF) as well as soot and sulfate fractions of the PM. In addition, the soot residing in the wall of the wafer was examined under an optical microscope illuminated with Ultraviolet light and an Environmental Scanning Electron Microscope (E-SEM) to determine the bulk soot penetration depth for each loading condition. It was found that higher filtration velocity results in higher wall loading with approximately the same penetration depth into the wall. PM characteristics impacted both wall loadingmore » and soot cake layer characteristics. Results from imaging analysis indicate that soot the penetration depth into the wall was affected more by PM size (which changes with engine operating conditions) rather than filtration velocity.« less

Vortex ring-like structures in gasoline fuel sprays under cold-start conditions

Abstract: A phenomenological study of vortex ring-like structures in gasoline fuel sprays is presented for two types of production fuel injectors: a low-pressure, port fuel injector (PFI) and a high-pressure atomizer that injects fuel directly into an engine combustion chamber (G-DI). High-speed photography and phase Doppler anemometry (PDA) were used to study the fuel sprays. In general, each spray was seen to comprise three distinct periods: an initial, unsteady phase; a quasi-steady injection phase; and an exponential trailing phase. For both injectors, vortex ring-like structures could be clearly traced in the tail of the sprays. The location of the region of maximal vorticity of the droplet and gas mixture was used to calculate the temporal evolution of the radial and axial components of the translational velocity of the vortex ring-like structures. The radial components of this velocity remained close to zero in both cases. The experimental results were used to evaluate the robustness of previously developed models of laminar and turbulent vortex rings. The normalized time, t 5t/tinit, and normalized axial velocity, Vvx(t) 5Vvx(ttinit)/Vvx(tinit), were introduced, where tinit is the time of initial observation of vortex ring-like structures. The time dependence of Vvx on t was approximated as Vvx(t) 5t 22.97 and Vvx(t) 5t ¯ 21.14 for the PFI and G-DI sprays respectively. The G-DI spray compared favourably with the analytical vortex ring model, predicting Vvx 5t 2a , in the limit of long times, where a 53/2 in the laminar case and a 53/4 when the effects of turbulence are taken into account. The results for the PFI spray do not seem to be compatible with the predictions of the available theoretical models.

Experimental study of recompression reaction for low-load operation in direct-injection homogeneous charge compression ignition engines with n-heptane and i-octane fuels:

Abstract: Experiments have been reported in the literature in which the low-load limit of a retention-mode HCCI engine operating on gasoline has been significantly extended by pre-processing of the fuel during negative valve overlap. This paper presents experimental studies in which this low-load-limit extension is demonstrated and characterized using simple, single-component hydrocarbon fuels with relatively well-known chemical kinetics. The model fuels were n-heptane and i-octane and this choice was made both because of the extensive work that has been undertaken to develop their chemical kinetic mechanisms and because these fuels span the range of ignitability that is likely to be of interest for HCCI engines.The experimental results reported here show that both fuels exhibit load extension to as low as 1 bar net indicated mean effective pressure when operated at high residual mass fractions, low equivalence ratios, and an appropriate choice of compression ratio (13 for n-heptane, 18 for i-octane). Near ...

Assessment of combustion in natural gas dual-fuelled compression ignition engines with dimethyl ether and rapeseed methyl ester pilot ignition

Abstract: Compression-ignition engines are known to be more efficient than similar-sized spark-ignition engines because of the higher compression ratios and leaner combustion. The emissions of soot and nitrogen oxides remain the main hurdle in the complete exploitation of these engines. Dual-fuelling is one means favoured for solving the emission problem, in which high-octane fuels are used as the main fuel which is ignited by a smaller pilot injection of diesel or another high-cetane fuel. These dual-fuel engines produceless particulate matter and nitrogen oxides than spark-ignition engines, while retaining the desired compression-ignition engine efficiency. In thepresent investigation, tests were conducted using a variety of renewable and non-renewable fuels for pilot injection. The pilot fuels employed wereconventional diesel, rapeseed methyl ester (known as biodiesel), and dimethyl ether, while natural gas was used as the main fuel. Biogas, or landfill gas, would be the renewable alternative. Pressure versus crank angle traces were obtained, together with their first and second derivatives. These were analysed to determine the crank angle at which ignition began. Diagrams that show the rate of reaction were also plotted for the same purpose. Here, the start of ignition is determined by the trace suddenly changingslope and rising above zero. Using these methods, the ignition delay was determined for different operating conditions and comparisons drawn for different pilot fuels. The characteristic shapes of rate-of-reaction curves were analysed highlighting differences in the combustion processes occurring in single- and dual-fuel diesel engine operation. Emissions data for different operating conditions were also obtained and analysed, showing a tendency for lower emissions of smoke and oxides of nitrogen but increased carbon monoxide and unburnt hydrocarbons to be produced in dual-fuelling. Carbon dioxide was also reduced

Micro- and macroscopic visualization of particulate matter trapping and regeneration processes in wall-flow diesel particulate filters

Abstract: Particulate matter trapping and regeneration processes in wall-flow diesel particulate filters (DPFs) without catalysts were investigated through micro- and macroscopic visualization experi...

Simultaneous reduction in cloud point, smoke, and NOx emissions by blending bioethanol into biodiesel fuels and exhaust gas recirculation

Abstract: Palm oil has the important advantage of productivity compared with other vegetable oils such as rapeseed oil and soybean oil. However, the cold flow performance of palm oil methyl ester (PME) is poorer than other vegetable-oil-based biodiesel fuels. Previous research by the current authors has shown that ethanol blending into PME improves the cold flow performance and considerably reduces smoke emission. The reduced smoke may be expected to allow an expansion in the exhaust gas recirculation (EGR) limit and lead to reduced oxides of nitrogen (NOx). This paper experimentally analyses the influence of EGR on smoke and NOx emissions with ethanol-blended PME.The results show that the combination of ethanol blending and EGR is effective in reducing NOx and smoke simultaneously without the thermal efficiency deteriorating. The smoke reduction can be attributed to an improved fuel—air mixing by an increased ignition delay owing to the low cetane number of ethanol and by a promoted fuel spray atomization ...

Light scattering technique for estimating soot mass loading in diesel particulate filters

Abstract: The real-time estimation of soot mass loading on diesel particulate filters (DPF) is essential to assure perfect and fuel efficient regeneration. Computer models based on the pressure drop across the DPF are usually installed in the engine control unit to estimate the soot mass loading during vehicle driving, but this approach is still subject to uncertainty about the lack of resources available. The aim of this study is to develop a portable instrument that can make real-time measurements of soot mass loading under transient mode for calibrating the models. The instrument is based on the light scattering technique: A laser beam illuminates diesel particles in a small exhaust sample and the intensity of scattered light from soot particles is reduced to soot mass concentration using calibration data obtained under steady engine operating conditions. It is demonstrated that the prototype instrument can measure the temporal variations of cumulative soot mass and filtration efficiency of a diesel part...

Combustion model reduction for diesel engine control design

Abstract: The subject of this work is the derivation of a simulation model for premixed charge compression ignition (PCCI) combustion that can be used in closed-loop control development. For the high...

Development of an improved urea-selective catalytic reduction-diesel particulate filter system for heavy-duty commercial vehicles

Abstract: Many heavy-duty commercial vehicles are now equipped with urea-selective catalytic reduction (SCR) systems, which can reduce NOx emissions sufficiently to meet the requirements of legislation such as Japan's New Long-term Diesel Emissions Regulations. However, in order to meet even stricter exhaust emissions regulations (and fuel consumption standards) due to be imposed in many parts of the world in the near future, urea-SCR systems with greater catalytic efficiency combined with diesel particulate filters (DPFs) will be needed. Therefore, in the study presented here the scope for enhancing the efficiency of a urea-SCR system was explored by optimizing the urea dosing system and injection strategies, and the gas flow in the exhaust pipe. However, since improving the catalysis parameters could have the greatest overall effect on conversion efficiency, work focused on modifying the catalyst materials to increase their adsorption capacity for the NH3 reducing agent, and thus increase the collision frequency between NOx and NH3 absorbed on the surface of the catalyst. In addition, the oxidation parameters of the oxidation catalyst were optimized, which enhanced the NOx conversion efficiency of the system, not only in a steady cycle but also in a transient cycle. Following these adjustments, a DPF-plus-SCR system with the new catalytic material delivered 90 per cent conversions of NOx and particulate matter to nitrogen and CO2 respectively, in the JE05 test cycle. In addition, a new concept, a miniaturized 'urea-SCR with DPF function system' was proposed and tested, which delivered 90% NOx conversion rates and 90% reductions in particulate matter emissions in the JE05 test cycle

Effects of spark-assistance on controlled auto-ignition combustion at different injection timings in a multicylinder direct-injection gasoline engine

Abstract: Controlled auto-ignition (CAI) combustion, also known as homogeneous charge compression ignition (HCCI) can be achieved by trapping residuals with early exhaust valve closure in a direct fuel injection in-cylinder four-stroke gasoline engines. CAI combustion is achieved by auto-ignition independent of spark discharge. However, it is found that, at loads with reduced trapped residuals, the presence of spark influences combustion. Therefore the effects of spark timing on the CAI combustion process were investigated through the introduction of spark. The effect on engine performance and the emission specific values were evaluated. The engine speed was maintained at 1500 r/min and lambda was kept constant at 1.2. It was found that with spark-assisted CAI, indicated mean effective pressure (IMEP), and indicated specific oxides of nitrogen (ISNOx) values increased as compared with CAI without spark. ISHC and ISCO values were lower for spark-assisted CAI as compared with CAI

An investigation of mixture formation and in-cylinder combustion processes in direct injection diesel engines using group-hole nozzles

Abstract: Mixture properties of the transient fuel spray injected by group-hole nozzles were quantitatively studied in a constant volume chamber via the laser absorption scattering (LAS) technique, a...

Virtual design of a novel two-stroke high-speed direct-injection diesel engine

Abstract: The paper reviews the virtual design process of an automotive high-speed direct-injection (HSDI) two-stroke diesel engine, developed at the Department of Mechanical and Civil Engineering (DIMeC) of the University of Modena and Reggio Emilia. The new concept of the engine is the tumble-supported and spray-controlled combustion system, which enables the adoption of loop scavenging without valves, and the use of a very simple and compact combustion chamber, carved in the engine head.The concept has been applied to a three-cylinder engine, with a capacity of 1050 cm3, supercharged by means of a Roots compressor and a variable geometry turbocharger. Some alternative configurations have been defined. Integrated one-dimensional and multidimensional computational fluid dynamics (CFD) simulations have been performed in order to optimize the main engine parameters, as well as to predict brake performance and emissions, in comparison with a reference four-stroke automobile diesel engine.Simulation results de...

Evaluation of reaction scheme at high initial temperature condition bypassing low-temperature reaction

Abstract: By using ‘contribution matrices’, the authors had clarified that a major reaction path during the thermal ignition preparation phase of dimethyl ether and n-heptane was a set of reactions named the ‘H2O2 reaction loop’, and suggested it may be a universal rule that the heat accumulated by this loop plays a dominant role in preparing a thermal ignition. In the present study, this suggestion was verified by using a fuel with a higher octane number, iso-octane, and by changing the initial temperature. It was verified in all cases that the ignition delay, a period of the thermal ignition preparation phase, depends on the H2O2 concentration at the beginning of this phase. Reaction path analyses showed that higher initial temperature conditions and skipping reactions in the low-temperature oxidation (LTO or cool flame) and negative temperature coefficient (NTC) range result in lower H2O2 concentrations and lower heat release during the thermal ignition preparation phase. Fuels with low and high octane n...

Lean NOx trap study on a light-duty diesel engine using fast-response emission analysers

Abstract: Storage and regeneration events have been studied using fast-response emission analysers (∼10 ms) for a lean NOx trap (LNT) fitted to a light-duty diesel engine. Tests were conducted at both low and high exhaust temperatures for various storage and purging periods. The use of fast-response analysers has provided detailed information during the short regeneration periods and as combustion switched between rich and lean operating modes. It has also enabled quantification of the storage, reduction, and overall conversion efficiencies, as well as the instantaneous trapping efficiency. With exhaust temperatures of 250 °C, storage efficiency was low (∼30 per cent). During purging, two distinct NO spikes (breakthroughs) were measured downstream of the LNT at the beginning and end of regeneration. For this LNT, the primary reducing mechanism is CO reacting with NO, but CO reacting with ceria and/or water, the water—gas shift reaction, is suspected. With exhaust temperatures of 400 °C, storage efficiencies...

Effect of injection timing on gasoline homogeneous charge compression ignition particulate emissions

Abstract: Particulate emissions from homogeneous charge compression ignition (HCCI) engines are often considered as negligible and the measurement of particulate matter (PM) with HCCI combustion syst...

Time-resolved measurements of low concentration aromatic hydrocarbons in diesel exhaust using a resonance enhanced multi-photon ionization method:

Abstract: Time-resolved measurements of the concentration of volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) in exhaust from a diesel vehicle fitted with an oxidation catalyst and operated in JE05 modeare performed at a sensitivity of 10?ppb using a supersonic jet/resonanceenhanced multi-photon ionization (Jet-REMPI) method. The concentrations of benzene, naphthalene, and phenol in exhaust from the test vehicle are measured before entering and after exiting from the oxidation catalyst. The total hydrocarbon (THC) is measured simultaneously using a constant volumesample (CVS) instrument fitted with a flame ionization detector (FID). Concentration changes of benzene, naphthalene and phenol are recorded at 1?sintervals and quantified using standard samples. Comparison of these signals with the real-time THC data shows that the time dependence of the individual species is almost the same as that of the THC before the oxidation catalyst but substantially different after.

Experimental study of pollutant emission reduction for near-stoichiometric diesel combustion in a three-way catalyst

Abstract: An experimental study was performed to examine the possibility of simultaneous reductions of NOx, hydrocarbons (HC), CO, and soot emissions for near-stoichiometric diesel combustion using a three-way catalyst and a diesel particulate filter (DPF). The DPF was deactivated in order to ensure the non-regeneration state and was just used as a soot filter trap upstream of the three-way catalyst. The goal of the research was to investigate the efficiency of emission conversion for an automotive diesel engine with a general three-way catalyst normally used for gasoline-powered vehicles under near-stoichiometric combustion operation. A modified single-cylinder engine was used for the experiments that considered throttled diesel combustion at 65-90kPa intake pressure to achieve near-stoichiometric conditions, and a common rail injection system with 90MPa injection pressure was used for mixture preparation and to avoid spray wall impingement. The results showed that the three-way catalyst was able to reduce NOx and CO emissions by up to nearly 98%, and the DPF trapped soot emissions up to 99.6% for near-stoichiometric operation. However, the particular palladium/rhodium catalyst formulation used in the study was less effective for HC emissions, which were only reduced by up to 57%. It is concluded that the use of the present proposed three-way catalyst/DPF aftertreatment system provides significant promise for future efficient, low emission diesel engines

Mixed-mode homogeneous charge compression ignition—direct injection combustion on common rail diesel engines: An experimental characterization

Abstract: In recent years, increasing attention has been given to the study of homogeneous charge compression ignition (HCCI) for automotive diesel engines, due to its potential to lower NOx and particulate matter (PM) emissions. However, controlling the combustion process and engineering a mixture preparation method that does not require significant modifications to the engine hardware are still significant barriers to a vehicle implementation. In this scenario, external mixture formation, performed through a diesel fuel atomizer, is a simple and reliable method to obtain a truly homogeneous charge, resulting in ultra-low NOx and negligible PM formation. This technology does not require any modification to the engine compression ratio or to the fuel direct injection (DI) system. The possibility of combining two separate fuelling systems allows for mixed-mode HCCI-DI combustion, where a diesel-type combustion is induced during HCCI operations, increasing the IMEP and the output engine torque. This would allow for a seamless transition from HCCI to conventional DI mode at high load, while retaining the HCCI combustion benefits on emissions at part-load engine operating conditions. Building on preliminary experimental results proving the feasibility and benefits of the HCCI combustion with external mixture preparation on a high-speed common rail diesel engine, the proposed work aims at extending the HCCI combustion characterization, in order to define an engine operating region for its application. Then, mixed-mode HCCI-DI operations were investigated as a strategy to overcome the IMEP limitations of pure HCCI combustion. The analysis of HCCI-DI combustion aims at studying the effect of important control parameters, such as EGR ratio and direct injection timing, on combustion and emissions, showing the effects of partial HCCI combustion at higher engine loads.

Enhancement of ignition characteristics of lean premixed hydrocarbon–air mixtures by repetitive pulse discharges:

Abstract: A newly developed small-sized inductive energy storage (IES) circuit that uses a semiconductor switch for the turn-off action is successfully applied to an ignition system in spark ignition engines operating under lean fuel–air ratios. This IES circuit can generate repetitive nanosecond pulse discharges. Experiments are conducted by means of a spherically expanding flame configuration for C3H8–air mixtures under various conditions. Findings show the investigated ignition system improves the inflammability of lean combustible mixtures in terms of extended flammability limits, shorted ignition delay time, and extended dilution limits, compared with conventional spark ignition systems.

Attempts to enhance the differential coefficients method for reconstruction of transient emissions from heavy duty vehicles

Abstract: Engine tailpipe emissions as measured by a sampling system and analyser do not clearly reflect the actual transient emissions from the engine at the tailpipe of the vehicle exhaust. With increasing demand for accurate emissions measurements, several research efforts are being made to compensate for the measurement distortions of the analyser system. The differential coefficients method is one such approach which reconstructs the input signal by approximating the analyser input as a linear combination of the output and the first two derivatives of the output. While the results with this approach were found to be acceptable, this paper focuses on the possibilities of improving the accuracy of the reconstruction by altering the ways in which the numerical derivatives are computed and by considering higher order derivatives in the linear combination. It was found that the use of backward differences in computing the numerical derivatives proved more effective than forward differences. Using higher ord...

Residual gas homogeneity measurements

Abstract: Planar laser-induced fluorescence (PLIF) of a dopant added to the fuel, which was well mixed with the intake air upstream of the engine, was used to investigate inhomogeneities that arise from the incomplete mixing of the intake charge with the residual gas left in the cylinder from the previous cycle. The residual gas fraction was independently measured using a fast-acting solenoid valve and a cylinder dumping technique. The experiments were performed on a four-stroke homogeneous-charge spark-ignition engine operating at light load. The PLIF data were shot-noise-limited, permitting filtering to reduce some noise artefacts; and to further reduce system-induced biases associated with pulse-to-pulse laser variations the data were ray-mean-normalized, i.e. normalized by the mean of the data along the laser propagation direction. The filtered results had excellent noise characteristics, with a signal-to-noise ratio in excess of 50:1, and allowed the low levels of mixture unmixedness to be identified. ...

Infrared absorption technique for measuring local fuel concentration near the spark plug of a port injection gasoline engine

Abstract: Abstract The mixture concentration in the vicinity of the spark plug at the time of spark ignition is a critical parameter for the performance of SI engines. Infrared absorption is often used to measure this parameter in firing cycles. Although it is well known that the mixture concentration near the spark plug is a primary factor explaining combustion stability in direct injection engines, the effect of the local mixture concentration has not been confirmed for nearly homogeneous mixtures. In this research, the mixture concentration in the vicinity of the spark plug was measured quantitatively using infrared absorption with an optical fibre sensor built into the spark plug of a port injection engine. Measurements were made across a range of air—fuel ratios for both steady state conditions at three different overall air—fuel ratios and for a rich-to-lean transient condition. It was experimentally confirmed that the mixture concentration near the spark plug has little impact on combustion stability for steady state operation with a homogeneous mixture distribution. It has also been confirmed that fibre-sensor-based infrared absorption can be used for cycle-by-cycle analysis of the local mixture concentration even for a homogeneous mixture distribution.