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The air/fuel ratio (AFR) is a key contributor to both the performance and emissions of an automotive engine. Its variation between cylinders - and between engine cycles - is of particular importance, especially during throttle transients. This paper explores the use of a fast flame ionisation detector (FFID) to quantify these rapid changes of in-cylinder composition in the vicinity of the spark gap. While this instrument actually measures fuel concentration, its results can be indicative of the AFR behaviour. Others have used the FFID for this purpose, but the planned test conditions placed special demands on the instrument. These made it prudent to explore the limits of its operating envelope and to validate the experimental technique. For in-cylinder sampling, the instrument must always be insensitive to the large pressure changes over the engine cycle. With the wide range of engine loads of interest here, this constraint becomes even more crucial.

For high-speed imaging a newly developed eight-fold CCD camera, which permits framing rates of up to one million pictures per second, was used to obtain pictures of the injected sprays during the operation of a diesel engine. For the particular case studied here the framing rate was set at 50,000 pictures per second. This rate was sufficient to resolve the temporal development of the sprays in the transparent version of the four-cylinder, in-line, 1.9 litre DI production diesel engine of Volkswagen. The advantage of the camera is that it needs no light pulses for illumination, but can operate with a continuous light source. Each of the CCD chips is arranged around a central eight face reflecting pyramid, which splits the light coming from the camera lens to each CCD chip. The chips can be shuttered freely (asynchronously) at programmable inter-frame spacings thus permitting operation with continuous illumination. In this particular case a 30 Watt halogen lamp was used.

Departures from optimum stoichiometry during transients (acceleration and deceleration) and cold start can lead to significant degradation in driveability and emissions control. Such departures occur as a result of a complex interplay between fuel transport mechanisms and the fuelling strategy. The relative contributions of several of these mechanisms are affected by fuel composition. To help understand these effects an open-path differential infra-red absorption technique has been used to monitor the transient evolution of the fuel vapour phase directly within the combustion chamber. The sensor projected a narrow infra-red beam which traversed the cylinder of an optical access engine along an open path under the head, and measured the path-integrated attenuation caused by absorption of the infra-red radiation by the fuel vapour. It operated in the near infrared (NIR) spectral region around 2.3 μm, an absorption band in hydrocarbon species containing methyl groups.

A new tool for quantitative measurements of fuel-air ratio in the combustion chamber of a spark ignition engine (FARLIF) has been achieved. This optical method is based on a new approach of PLIF, taking advantage of the quenching phenomenon. Toluene is present in a small proportion (5 % in iso-octane) and used as a tracer to visualise the fuel distribution. In a four stroke monocylinder engine equipped with optical access, instantaneous imaging of the air-fuel ratio is performed inside the cylinder during the compression phase. We study in the present paper the effect of different injection configurations on the charge homogeneity and on the cycle-by-cycle variations of the average equivalence ratio. Four injection timings, two positions of the injector and three rates of inlet manifold heating are tested.

A new modelling approach for premixed turbulent combustion has been developed and implemented in computing flow and combustion in axisymmetric engine cylinders. Turbulent transport is treated using a standard second-moment closure model based on Favre density-weighted averaging and the turbulent reaction rate is modelled using a novel laminar flamelet approach. The numerical method is based upon a modified PISO algorithm incorporating second-order bounded spatial differencing. The need for high numerical accuracy is investigated and quantified with reference to engine combustion calculations. The new model for the mean turbulent reaction rate is shown to capture correctly the qualitative behaviour of the flame near to a solid wall, in marked contrast to many existing models. The superiority of the second-moment turbulence model is demonstrated by direct comparison with a standard eddy-viscosity model using an engine combustion test case.

The fluid flow characteristics inside compound silicon micro machined port fuel injector nozzles were analyzed through the use of computational fluid dynamics (CFD). This study was undertaken in order to gain a better understanding of the fluid mechanics taking place in the compound orifice plate. In addition, the calculated computational results will be used to predict the fuel spray patterns and sauter mean diameters of the sprays. The influence of orifice plate geometry on calculated turbulent kinetic energies and fuel spray patterns was also studied and will be discussed. The results of this investigation indicate that the fluid flow characteristics inside the compound silicon micro machined port fuel injector nozzle are influenced by the geometries of the compound orifice plate, and that the flow characteristic inside the orifice plate effect the type of spray produced by the injector.

The deposition of an impinging diesel spray is studied experimentally to improve the understanding of wall-spray-interactions. Experiments are performed under atmospheric pressure conditions as well as in a pressure chamber filled with nitrogen where the pressure is varied between 0.1 Mpa and 2 MPa. In both cases a light reflection method is used to observe size, shape and time development of the wetting imprints of the spray. The duration of the injection pulse is 2 ms. The mean injection pressure is 47 MPa. Additional experiments under atmospheric pressure conditions are performed without the pressure chamber. Here a shadow-graph optic is added to the apparatus to allow the simultaneous observation of the impinging spray and the wetted area of the wall. It is found that the diameter of the impinging spray increases faster than that of the imprint which suggests that the wall spray separates from the wall.

Multidimensional computations were carried out to simulate the in-cylinder fuel/air mixing process of a direct-injection spark-ignition engine using a modified version of the KIVA-3 code. A hollow cone spray was modeled using a Lagrangian stochastic approach with an empirical initial atomization treatment which is based on experimental data. Improved Spalding-type evaporation and drag models were used to calculate drop vaporization and drop dynamic drag. Spray/wall impingement hydrodynamics was accounted for by using a phenomenological model. Intake flows were computed using a simple approach in which a prescribed velocity profile is specified at the two intake valve openings. This allowed three intake flow patterns, namely, swirl, tumble and non-tumble, to be considered. It was shown that fuel vaporization was completed at the end of compression stroke with early injection timing under the chosen engine operating conditions.

A model of turbulent premixed flame initiation and early stage of propagation is proposed. Initiation submodel consists in representing of spark action with the heat deposit of the energy and duration appropriate for conditions relevant to SI engine, that is with the spark duration being non-negligible compared with turbulent time-scale. Chemistry is represented with reduced kinetics scheme of six reactions coupled with the pdf approach. The results of simulations obtained with this model are discussed. In particular, they show the model proposed is able to yield reasonable values for low concentration limits of ignition as well as critical spark energy needed to obtain self-sustaining flame propagation.

Temperature variation and heat transfer phenomena in the intake port of a spark ignition engine with port injection play a significant role in the mixture preparation process, especially during the warm up period. Cold temperatures in the intake port result in a large amount of liquid-fuel film. Since the liquid-fuel film responds at a slower speed than the gas-phase flow during transient operations, the liquid-fuel film acts as a fuel sink (or source) and can degrade the vehicle's driveability, fuel economy, and emissions control. In this work, a one-dimensional, unsteady, multicomponent, multiphase flow model has been developed to study the mixture formation process in the intake port for a modern, multipoint-fuel-injection, gasoline engine. The droplet, liquid film and gas-phase mixture temperature variations and the effects of charge air, initial fuel and port wall temperatures involved in generating the air-fuel mixture are examined.

A Lagrangian random vortex-boundary element method has been developed for the simulation of unsteady incompressible flow inside three-dimensional domains with time-dependent boundaries, similar to IC engines. The solution method is entirely grid-free in the fluid domain and eliminates the difficult task of volumetric meshing of the complex engine geometry. Furthermore, due to the Lagrangian evaluation of the convective processes, numerical viscosity is virtually removed; thus permitting the direct simulation of flow at high Reynolds numbers. In this paper, a brief description of the numerical methodology is given, followed by an example of induction flow in an off-centered port-cylinder assembly with a harmonically driven piston and a valve seat situated directly below the port. The predicted flow is shown to resemble the flow visualization results of a laboratory experiment, despite the crude approximation used to represent the geometry.

A numerical study was performed to elucidate the link between cyclic combustion variations in spark-ignition engines and instabilities in the non-linear processes occurring during the combustion. The instabilities in combustion were investigated by examining the response of a two-zone phenomenological combustion models to small deviations of mixture and flow conditions in the cylinder, such as the turbulence intensity at ignition, the overall equivalent ratio and the local equivalent ratio around the ignition site. The predicted combustion characteristics were validated and in good agreement with experimental data obtained from a single-cylinder research engine. The study suggested that the main deficiency of combustion in spark-ignition engines is the point-source ignition: it gives rise to slow development of initial flame; variations of the intermittent combustion process can occur when initial conditions at the ignition site are not repeatable from cycle to cycle.

Our earlier experimental study has shown that exhaust unburnt hydrocarbon emissions from spark-ignition engines can be reduced effectively by using in-cylinder catalysts on the surface of the piston top-land crevice. In order to improve the understanding of the process and mechanism by means of which unburnt hydrocarbon emissions are reduced, a phenomenological mathematical model was developed for catalytic oxidation processes in the piston-ring-pack crevice. This paper describes in details the modelling of the processes of the gas flow, mass diffusion and reaction kinetics in the crevices. The flow in the crevices is assumed to be isothermal and at the temperature of the piston crown surface. The overall rate of reaction is calculated using expressions for mass diffusion for laminar flows in channels and a first-order Arrhenius-type expression for catalytic reaction kinetics of hydrocarbon oxidation over platinum.

The influence of fuel quality on oxidation exhaust catalyst (OEC) efficiency in decreasing emissions of carbon monoxide, total hydrocarbons and total particulate matter (PM) from diesel cars has been investigated. Both in-house test results and further interpretation of published chassis dynamometer data have been utilised. Intrinsic OEC activity, which depends on exhaust gas temperatures, is shown to be largely unaffected by fuel quality, other than sulphur content. OECs affect PM emissions by changing the ratio of the soluble organic fraction to fixed carbon within engine-out PM. This ratio is strongly influenced by engine design and operation mode and to a lesser extent by fuel cetane number.

A combustion-based analytical method, initially developed by the Southwest Research Institute (SwRI) referred to as the Constant Volume Combustion Apparatus (CVCA), has been further researched/developed by an SwRI licensee (Advanced Engine Technology Ltd.) as an Ignition Quality Tester (IQT) for laboratories and refineries. The IQT software/hardware system permits rapid and precise determination of ignition quality for middle distillate fuels. Its features, such as low fuel volume requirement, complete test automation, and self-diagnosis, make it highly suitable for commercial oil industry and research applications. Operating and test conditions were examined in the context of providing a high correlation with cetane number (CN), as determined by the ASTM D-613 method. Preliminary investigation indicates that the IQT results are highly repeatable (± 0.30 CN), providing a high sensitivity to CN variation over the 33 to 58 CN range.

The influence of fuel characteristics on particulate emissions has been widely investigated. In this paper, the effect of different fuel properties on particulate emissions has been reviewed. The effect of fuel sulphur has been reported to have linear-relationship with the sulphate content of particulates. Combustion system, engine loading etc. were found to have weak contribution to the sulphate content variation. The results and analysis of various studies showed that the aromatic content had little influence on particulate emissions particularly in DI engines of modern design. The results from a number of investigations show that the key fuel property influencing particulate matter (PM) is the density.

A simple, relatively short and inexpensive screening test method has been developed for evaluation of available detergent/dispersant diesel fuel additives. The screening test is based on experiments of running a laboratory diesel engine in a pre-determined regime(load cycle). The engine is a single cylinder, 4-stroke DI, naturally aspirated and air cooled. It is coupled to a generator feeding electrical heaters as the load. The test rig is controlled electronically to enable fully automatic test bench operation, including start/stop, load change, emergency shut-down, etc. The experiments were performed by running the engine on a reference base fuel and then the same fuel with different detergent additives. The nozzle of the fuel injector was checked for clogging by air flow measurements, using the ISO-4010 test rig.

This paper describes the use of a modified quasi-dimensional spark-ignition engine simulation code to predict the extent of cycle-to-cycle variations in combustion. The modifications primarily relate to the combustion model and include the following: 1. A flame kernel model was developed and implemented to avoid choosing the initial flame size and temperature arbitrarily. 2. Instead of the usual assumption of the flame being spherical, ellipsoidal flame shapes are permitted in the model when the gas velocity in the vicinity of the spark plug during kernel development is high. Changes in flame shape influence the flame front area and the interaction of the enflamed volume with the combustion chamber walls. 3. The flame center shifts due to convection by the gas flow in the cylinder. This influences the flame front area through the interaction between the enflamed volume and the combustion chamber walls. 4. Turbulence intensity is not uniform in cylinder, and varies cycle-to-cycle.

We have developed a new wall wetting model to predict the transient Air/Fuel ratio excursion in a port fuel injected (PFI) engine due to changes in air or fuel flow. The quasi-dimensional model accounts for fuel films both in the port as well as in the cylinder of a PFI engine and includes the effects of back-flow on the port fuel films to redistribute and vaporize the fuel. A multi-component fuel model is included in the simulation; it gives realistic fuel behavior and allows the effects of different fuel distillation curves to be studied. The multi-component fuel model calculates the changing composition of the fuel puddles in the port and cylinder during the cycle. The inclusion of an in-cylinder fuel film allows the model to be used for cold start conditions down to 290 K. The model uses the Reynold's analogy to calculate the fuel vaporization process and uses a boundary layer calculation to solve for the liquid film flow.

An advanced and practical fuel injection control system to reduce exhaust gas emissions has been developed. This control uses an exhaust air-fuel ratio (EAFR) sensor and a heated exhaust oxygen (HEO) sensor. The air fuel ratio of exhaust gas is precisely converged to stoichiometry. The integrated deviation of the mass of fuel inducted into the cylinder is rapidly converged to zero, so as to maximize the conversion efficiency of catalysts. The controller is derived from the models that express the dynamic phenomena. The experimental results show the effectiveness of this system for future exhaust emissions and enhanced evaporative emissions.