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The numerical methodology used to predict the flow inside pressure-swirl atomizers used with gasoline direct injection engines and the subsequent spray development is presented. Validation of the two-phase CFD models used takes place against film thickness measurements obtained from high resolution CCD-based images taken inside the discharge hole of a pressure swirl atomizer modified to incorporate a transparent hole extension. The transient evolution of the film thickness and its mean axial and swirl velocity components as it emerges from the nozzle hole is then used as input to a spray CFD model predicting the development of both non-evaporating and evaporating sprays under a variety of back pressure and temperature conditions. Model predictions are compared with phase Doppler anemometry measurements of the temporal and spatial variation of the droplet size and velocity as well as CCD spray images.

The electrical characteristics of transistorized coil ignition (TCI) and capacitor discharge ignition (CDI) systems were investigated in spark-ignited quiescent and flowing propane/air mixtures within an optically-accessible, cylindrical constant-volume combustion chamber. Under quiescent flow conditions, the initial pressure, temperature and equivalence ratio of the mixture as well as the spark gap width and geometry were varied systematically in order to examine the relationship between ignition characteristics and flame initiation and development. The effect of the flow in the spark gap on the electrical characteristics of the ignition system, mixture ignitability and flame development was also examined by varying the pre-ignition mean flow and turbulence as well as the spark plug orientation relative to the mean flow.

A dense-particle Eulerian-Lagrangian stochastic methodology, able to resolve the dense spray formed at the nozzle exit has been applied to the simulation of evaporating diesel sprays. Local grid refinement at the area where the spray evolves allows use of cells having sizes from 0.6 down to 0.075mm. Mass, momentum and energy source terms between the two phases are spatially distributed to cells found within a distance from the droplet centre; this has allowed for grid-independent interaction between the Eulerian and the Lagrangian phases to be reached. Additionally, various models simulating the physical processes taking place during the development of sprays are considered. The cavitating nozzle flow is used to estimate the injection velocity of the liquid while its effect on the spray formation is considered through an atomisation model predicting the initial droplet size.

Mixed-lubrication models comprising of Patir and Cheng's [1,2] average Reynolds equation and Greenwood and Tripp's [3] asperity interaction formulations have hitherto been widely used in predicting piston-ring performance. In this paper a number of models have been developed to allow mixed-lubrication of both Newtonian and shear thinning fluids to be simulated. Lubricating action usually involves two anisotropic solid surfaces of statistically different profiles. Various forms of the average Reynolds equation and the asperity interaction models require parameters representing the composite surface roughness and profile parameters at the contact. Here a strategy for determining these equivalent composite parameters is presented. Mathematical simulations indicate that when the composite RMS and composite summit RMS roughness of the contact approach the same value, the performance of the mix-lubrication model becomes dominated by the asperity interaction formulation.

The diesel engine is the most efficient user of fossil fuels for vehicle propulsion and seems to best fulfill the requirements of the future. It is for this reason that Volkswagen has initiated a very broad research programme for diesels. The purpose of this paper is to build a bridge between fundamental research and technical developments which could allow evaluation of the prospects of direct- injection diesels as powerplants of choice for passenger cars in the turn of the century. The current knowledge on mixture formation, combustion and pollutant formation in diesel engines is presented and discussed with special emphasis given to the concept of the direct-injection diesel engine.

An enlarged transparent model of a six-hole vertical diesel injector has been manufactured in order to allow flow measurements inside the sac volume and the injection holes to be obtained using a combination of laser Doppler velocimetry (LDV) and the refractive index matching technique under steady state conditions. The measurement points were concentrated in the sac volume close to the entrance of the injection holes as well as inside them on a vertical plane passing through the axis of two injection holes for two different needle lifts. The velocity flow field was characterized in terms of the mean velocity and the turbulent intensity. The results revealed that, under certain conditions, cavitation may occur in the recirculation zone formed at the entrance to the hole since the pressure in this region can reach the value of the vapor pressure of the flowing liquid; this was found to strongly depend on the needle lift and eccentricity.

Heat release analysis, ion current and laser Doppler velocimetry methods are combined to examine the effect of pre-spark turbulent mixture motion on flame propagation and combustion characteristics in the four-valve pentroof combustion chamber of a spark ignition engine. Two inlet port configurations leading to different strengths of induction-generated tumbling vortices are considered with emphasis on lean mixture operation under partial load conditions. The results show a good correlation between mixture turbulent characteristics at ignition and flame development, flame propagation rate, combustion duration and cyclic variability. It is shown that turbulence enhancement through induction-generated tumble counterbalances the lean mixture ignition delay by enhancing the flame propagation speed, leading to extension of the engine lean operating limits.

A laser Doppler velocimeter, flame ionisation gauge and piezoelectric transducer have been used to measure two components of velocity, arrival of the flame front and pressure in the cylinder of a four-stroke spark ignition engine. The engine was operated with a sequence of five firing and ten non-firing cycles with the former having an equivalence ratio of 0.9 and giving rise to a misfire, a subsequent high-charge cycle, and three normal-charge cycles. The resulting fast- and slow-burn cycles were identified readily in terms of maximum pressure and flame-arrival times. The two-dimensional velocity vectors suggest that the flame fronts were initially spherical and subsequently distorted by the expansion of burned gas with increase in velocity fluctuations.

The injection rate signals from a commercial diesel fuel injection system, based on a distributor pump driven by a DC motor, were characterised independently and consecutively by two injection rate meters based on the Zeuch and Bosch methods. The signals were first analysed in terms of their shot-to-shot variations over 64 consecutive injections and the correlations between needle lift and injection rate over a range of pump speeds and loads quantified by Fast Fourier Transform. A direct comparison of the injection rate signals on a cycle-resolved basis was achieved by connecting two consecutive injectors from the pump-line-nozzle injection system to a Bosch- and a Zeuch-based injection rate meters. The signals were acquired over a large number of injections in terms of mean and rms of the injected quantity, mean injection rate, maximum injection rate, average cumulative fuel injected and average injection duration.

The spatial and temporal characteristics of the non-evaporating diesel sprays injected into the atmosphere through two pump-pipe-nozzle systems used in small DI diesel engines have been investigated by laser-single-beam deflection and phase-Doppler anemometry (PDA). The injectors used for these tests comprised a single-spring and a prototype two-spring multihole-type nozzle. The results provided quantitative information about the effect that the second spring exerts on injection duration and spray characteristics, i.e. it increases injection duration and, at the same time, improves fuel atomisation during the main injection period.

A visualization study using shadowgraphy was performed in an optically-accessible, cylindrical constant-volume combustion chamber to identify the mechanism of flow/flame interaction in spark-ignited, lean propane-air mixtures. The effect of the flow on flame initiation and propagation was examined by varying the pre-ignition mean flow and turbulence within a range typical of modern four-valve spark-ignition (SI) engines, as well as the spark plug orientation relative to the mean flow. The initial flame development was quantified in terms of 2-D images which provided information about the projected flame area and the displacement of the flame center as a function of flow conditions, time from the spark initiation and spark plug orientation. The results showed that high mean flow velocities and turbulence levels can shorten combustion duration in lean mixtures and that the positioning of the ground electrode can have an important effect on the initial kernel formation.

The continuity and momentum equations for a pump-pipe-nozzle fuel injection system have been solved by a computer simulation program employing both the Runge-Kutta method and the more widely used method of characteristics. This allows the prediction of fluid phenomena and the dynamics of the mechanical components based on the geometry of the FIE system. The simulation includes the effects of possible cavitation, system leakage as well as variations in fuel density and bulk modulus. The computer model has been made as flexible as possible by using a modular format and inputting the system parameters from external files or dialog boxes. Experimentation was done on a Bosch VE type distributor pump supplying a multi-hole type nozzle which allowed preliminary evaluation of the model by comparing the predicted and measured injection rates and line pressures over a range of pump speeds and loads.

The in-cylinder flow during induction and compression in the pentroof chamber of a four-valve, single-cylinder, spark-ignition optical engine was quantified by LDV and correlated with combustion development especially under lean mixture conditions. The tumble-generating capacity of the cylinder head was first characterised by a tumble adaptor under steady flow conditions and, subsequently, enhanced by two sleeves introduced into the intake ports which generated a stronger tumbling motion.

The spatial and temporal characteristics of transient diesel sprays impinging on unheated and heated walls were investigated by phase-Doppler anemometry (PDA) and the heat-transfer distribution in the vicinity of the impingement region was determined by fast response thermocouples. The results have provided quantitative evidence about the effect that the presence of the flat wall exerts on the spray characteristics. For example, independent of the thickness of the liquid film, the wall rearranges the droplet size distribution of the free spray with droplet collision and coalescence playing an important role in both the droplet redistribution and in the development of the wall-jet. Droplet sizes were reduced and mean tangential velocities increased with wall temperature at the upstream side and at the front of the wall-jet, respectively.

A constant-volume combustion chamber was used to examine injection of a small quantity of slightly rich fuel/air mixture towards the spark plug around the time of ignition, in an overall very lean mixture rotating at velocities representative of modern spark-ignition engines. The results show that it is possible to achieve 100% ignitability with overall air-fuel ratios in excess of 50 and much faster burn rates than those with initially homogenous mixtures of the same equivalence ratio with high swirl and turbulence. The advantages of this method of local charge stratification have been demonstrated in terms of both pressure measurements and shadowgraphs of the early flame development while the transient characteristics of the injected rich mixture at the spark plug gap were monitored by a fast flame ionization detector.

Two optical single-cylinder spark-ignition engines equipped with two- and four-valve cylinder heads were used to examine the flow and flame interaction under lean mixture conditions. Images of the developing flame under quiescent, swirl, low tumble and high tumble flow conditions corresponding to a wide range of mean velocity and turbulence levels around the time of ignition were obtained with an image-intensified CCD camera using the light radiated by the flame and the flow in the vicinity of the spark plug was quantified by laser Doppler velocimetry. In the case of the tumbling flow, the flame images were software-processed to allow estimation of the total flame area, the displacement of its centre as a function of crank angle and their correlation with the cylinder pressure.

A computer model solving the 1-D flow in a typical fuel injection system for direct-injection diesel engines is presented. A Bosch distributor - type VE pump connected to four Stanadyne pencil - type nozzles has been used to validate the computer model over a wide range of operating conditions. Validation of the developed computer code has been performed for eight representative test cases. The predicted values which were compared with the experimental ones include the pumping chamber pressure, the line pressure, the needle lift and the injection rate. Results using as input the measured pumping chamber pressure are also presented in order to identify the error in the injection rate signal attributed to the difference between the simulated and the experimental pumping chamber pressure. In addition, the total fuel injection quantity for pump speeds between 500 and 2000 rpm and lever positions between 20% to 100% was calculated and compared with measurements.

The spray/wall interaction in small direct-injection diesel engines employing swirl was simulated in a bench-type experiment by a steady cross-flow of air acting on a transient diesel spray impinging normally onto a heated and unheated flat plate under atmospheric conditions. The droplet size and velocity characteristics in the radial wall-jet formed on the plate after spray impingement were investigated by phase-Doppler anemometry and the spray/wall heat transfer during impingement was measured using fast-response thermocouples. The results showed that the mechanism of secondary atomisation of the impinging droplets was altered as droplets from the approaching spray were entrained by the cross-flow, while the spray/wall heat transfer was reduced due to the lower droplet flux reaching the wall. Based on the approaching droplet velocity and size characteristics and wall temperature, an empirical correlation has been derived between the flow and heat transfer parameters.

Measurements are presented of droplet characteristics and air velocity in the cylinder of a 0.36 litre four valve engine, equipped with an sohc VTEC-E valve train and port injection. The results show that injection at crank angles, θinj(s), when the inlet valve is open results in most of the liquid volume flux being in the form of droplets with Sauter mean diameter between 20 and 30 mm which strikes the sleeve up to about 2.5 cm below the exhaust valves, thus generating a locally rich cloud there. The amount of liquid phase gasoline passing through the plane 16 mm below the spark plug gap increases with θinj(s) up to 50 CA after intake TDC and this, together with the crank angle of droplet arrival and vapour generation, controls stratification of the gaseous fuel phase. The optimum injection time is when the fuel-rich cloud is generated so that the tumble vortex convects it to the spark plug at the time of ignition.

The effect of various levels of exhaust gas recirculation (EGR) on the combustion characteristics has been investigated in the four-cylinder 1.9L direct-injection optical VW diesel engine in terms of the cylinder pressure, flame development, temperature and KL-factor distributions. Images of the developing flame under twelve engine operating conditions including 1000rpm/idle, 2000rpm/2 bar bmep and 2000rpm/10 bar bmep at 0%, 30% and 50% EGR-rates were obtained by means of two CCD cameras, in the absence of external illumination, with and without interference filters in the optical path. Analysis of these images has revealed that increased EGR rates lead to increased cyclic pressure variations during the warm-up period of the engine, reduced and more fragmented high-temperature regions, reduced flame core temperatures, generally reduced soot oxidation rates but similar ignition delay times.