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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.

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.

A computer model simulating the flow in fuel injection systems has been used in order to investigate the fuel injection processes in an in-line pump-based fuel injection system for direct-injection diesel engines. The model is one-dimensional and it is based on the mass and momentum conservation equations for the simulation of the fuel flow and on the equilibrium of forces for the simulation of the mechanical movements of the valves present in the system. The fuel injection system tested comprised an in-line pump whose characteristics were examined by using as input the measured line pressure signal and by modeling the pump operation itself as well as the fuel flow through single- and two-stage injectors. For the validation of the model, extensive comparison with experimental data has been performed for a wide range of pump operating conditions.

A production six-hole conical sac-type nozzle incorporating a quartz window in one of the injection holes has been used in order to visualize the flow under cavitating flow conditions. Simultaneous variation of both the injection and the back chamber pressures allowed images to be obtained at various cavitation and Reynolds numbers for two different fixed needle lifts corresponding to the first- and the second-stage lift of two-stage injectors. The flow visualization system was based on a fast and high resolution CCD camera equipped with high magnification lenses which allowed details of the various flow regimes formed inside the injection hole to be identified. From the obtained images both hole cavitation initiated at the top inlet corner of the hole as well as string cavitation formed inside the sac volume and entering into the hole from the bottom corner, were identified to occur at different cavitation and Reynolds numbers.

Laser induced fluorescence (LIF) was used in the cylinder liner of a firing single-cylinder direct-injection diesel engine to characterise the development of the lubricant film during the first 200 engine cycles under cold-start conditions. The results have provided information on the rate of oil film development which has proved to be a highly unsteady process due to the complicated oil transport processes through the ring-pack.

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.

Local measurements of the mean and rms velocities have been obtained by laser Doppler velocimetry in the coolant passages of a transparent model of a Ford 2.5L diesel cylinder head and block at a steady flowrate of 6.83 × 10-4 M3/s. The simulation of the coolant fluid by a mixture of hydrocarbon fluids at a predetermined constant temperature allowed accurate matching of the refractive index to that of the acrylic model, thus providing optical access for LDV measurements of the internal flow in sensitive areas where cooling is essential to prevent metal-fatigue failure. The results were obtained in sufficient detail to allow further validation of CFD coolant flow models.

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 test-rig has been developed to simulate under idealised conditions the lubricating action between the piston-ring and the cylinder-liner in reciprocating engines. Complications arising in production engine piston-assemblies such as lubricant starvation, ring and piston dynamics, thermal and elastic deformations and blowby can thus be avoided so that the lubricant film characteristics are examined in isolation. The lubricant film thickness and friction at the piston-ring/liner interface were simultaneously measured throughout the stroke as a function of speed and load and compared with the solution of the Reynolds equation for a range of boundary conditions. The examined conditions included the Swift-Stieber (Reynolds), the separation and limiting cases of the Floberg and the Coyne & Elrod boundary conditions using a numerically efficient general purpose program.

Laser Doppler velocimetry, phase Doppler anemometry and Mie scattering were applied to a single-cylinder, four-valve, spark-ignition gasoline research engine equipped with a fully transparent liner and piston, to obtain information about the tumble flow and the droplet size and velocity distributions during induction and compression, for lean air/fuel mixture ratios of 17.5 and 24 and with closed-valve and open-valve fuel injection. The mixture distribution obtained with the two injection strategies was correlated with flame images, pressure analysis and exhaust emissions which confirmed the advantages of combining open-valve injection with tumble to allow stable and efficient engine operation at an air/fuel ratio of 24 through charge stratification and faster flame growth.

A diesel spray model has been developed and validated against experimental data obtained for different injection and surrounding gas conditions to allow investigation of the relative importance of the different physical processes occurring during the spray development. The model is based on the Eulerian-Lagrangian approximation and the Navier-Stokes equations, simulating the gas motion, are numerically solved on a collocated non-uniform curvilinear non-orthogonal grid, while the spray equation is solved numerically using a Lagrangian particle tracking method. The injection conditions are determined by another recently developed model calculating the flow in the fuel injection system, the sac volume and injection holes area which accounts for the details of the injection velocity, the fuel injection rate per injection hole and occurrence of hole cavitation. Thus, differences between the sprays from inclined multihole injectors can be simulated and analysed.

The flow structure in a four-stroke model engine motored at 200 rpm with a compression ratio of 3.5 has been investigated. Ensemble-averaged axial and swirl mean and rms velocities have been obtained by laser-Doppler anemometry downstream of an axisymmetrically located single valve with 30 and 60 degree seat angles and various lifts, with and without induction swirl. In all cases, the intake-generated flow structure in the axial plane disappears by the time the inlet valve closes and results in nearly homogeneous turbulence during compression with levels of 0.5–0.7 times the mean piston speed. The swirling flow, however, which is induced by means of vanes, persists through the compression stroke, evolving from a spiralling motion early during intake into solid body type of rotation near TDC of compression, with associated swirl ratios increasing with valve lift.

The effect of multiple-injection strategy on nozzle hole cavitation has been investigated both experimentally and numerically. A common-rail Diesel injection system, used by Toyota in passenger car engines, has been employed together with a double-shutter CCD camera in order to visualise cavitation inside a submerged and optically accessible (in one out of the six holes) real-size VCO nozzle. Initially the cavitation development was investigated in single injection events followed by flow images obtained during multiple injections consisting of a pilot and a main injection pulse. In order to identify the effect of pilot injection on cavitation development during the main injection, the dwell time between the injection events was varied between 1.5-5ms for different pilot injection quantities. The extensive test matrix included injection pressures of 400 and 800bar and back pressures ranging from 2.4 up to 41bar.

Direct flame imaging and pressure analysis were applied to the combustion of gasoline and compressed natural gas (CNG) in a single-cylinder, four-valve spark-ignition engine equipped with optical access via quartz windows in the cylinder liner and piston crown. Tests were performed at three engine speed/load conditions and at equivalence ratios of 1.0, 0.9 and 0.8. The four-valve head incorporated two different port geometries, with and without metal sleeves to deflect the intake air flow, in order to investigate the effect of tumble strength on combustion and engine-out emissions of unburned hydrocarbons and NOx. The results showed that sleeving of the intake ports produced a significant increase in IMEP and a reduction in CoV IMEP for both CNG and gasoline, due to the greatly reduced bum duration.

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 predictive capability of Lagrangian and Eulerian multi-dimensional computational fluid dynamics models accounting for the onset and development of cavitation inside Diesel nozzle holes is assessed against experimental data. These include cavitation images available from a real-size six-hole mini-sac nozzle incorporating a transparent window as well as high-speed/CCD images and LDV measurements of the liquid velocity inside an identical large-scale fully transparent nozzle replica. Results are available for different cavitation numbers, which correspond to different cavitation regimes forming inside the injection hole. Discharge coefficient measurements for various real-size nozzles operating under realistic injection pressures are also compared and match well with models' predictions.

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.

Measurements of flow, spray, combustion and performance characteristics are reported for a Hydra direct-injection diesel, based on the Ford 2.5 L, engine and equipped with a variable-swirl port, a unit fuel injector and optical access through the liner and piston. The results provide links between the pre-combustion and combustion flow and, at the same time, between purpose-built single-cylinder optical engines and multi-cylinder production engines of nearly identical combustion chamber geometry. In particular, the spray penetration was found to depend on engine speed, rather than load, with velocities up to around 260 m/s at atmospheric pressure and temperature which are reduced by a factor of 2.5 under operating conditions and seem to be unaffected by swirl. The duration of combustion was reduced with increasing swirl and ignition delay increased linearly with engine speed.

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.

An investigation into the spray structure generated by two swirl pressure atomisers under various operating conditions in a constant-volume chamber and the in-cylinder flow pattern in an optical research direct-injection gasoline engine has been performed using CCD camera and laser Doppler velocimetry, respectively. The results provided detailed information about the effect of back pressure on the spray structure generated by the two injectors and the in-cylinder flow field which the sprays encounter following fuel injection into the cylinder during the induction and compression strokes.