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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.

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 laser-induced fluorescence (LIF) system has been developed to obtain measurements of the instantaneous lubricant film thickness in the piston-cylinder assembly of a firing single-cylinder, direct-injection diesel engine. Measurements were made at top-dead-centre (TDC), mid-stroke and bottom-dead-centre (BDC) position by means of three fibre optic probes inserted into the cylinder liner and mounted flush with its surface. Following extensive repeatability tests, the cycle-averaged lubricant film thickness was estimated for different multi-grade oils as a function of engine speed, load and temperature. The results quantified the dependence of the film thickness ahead, under and behind the piston rings on oil chemistry and viscometric properties, thus confirming the important role of the LIF technique in the development and formulation of new engine oils.

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.

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.

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.

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 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.

An optical single-cylinder four-valve high speed DI Diesel engine equipped with a high-pressure electronic fuel injection system has been used to obtain information about the spray development, combustion and exhaust emissions (NOx and smoke levels) for a range of operating conditions corresponding to engine speeds between 600 and 1800 rpm, injection pressures up to 1200 bars and fuel injection quantities from idle to full load. Two six-hole vertical mini-sac type injection nozzles with different hole sizes have been employed in order to investigate the effect of nozzle hole diameter on spray formation, combustion and exhaust emissions. Parallel to the experimental programme, a computational investigation of the fuel flow distribution inside the injection system and of the subsequent spray characteristics has been performed in order to assist in the interpretation of the results.