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A sheet of laser light from a frequency-doubled Nd-YAG laser (λ = 532 nm) approximately 150 μm thick is shone through the cylinder of a single cylinder internal combustion engine. The light scattered by the fuel spray is collected through a quartz window in the cylinder and is imaged on a 100 × 100 diode array camera. The signal from the diode array is then sent to a microcomputer for background subtraction and image enhancement. The laser pulse is synchronized with the crank shaft of the engine so that a picture of the spray distribution within the engine at different times during injection and the penetration and development of the spray may be observed. The extent of the spray at different positions within the chamber is determined by varying the position and angle of the laser sheet with respect to the piston and the injector.

A three-dimensional model for premixed- charge naturally-aspirated rotary engine combustion is used to identify combustion chamber geometries that could lead to increased indicated efficiency for a lean (equivalence ratio =0.75) natural gas/air mixture. Computations were made at two rpms (1800 and 3600) and two loads (approximately 345 Kpa and 620 Kpa indicated mean effective pressure). Six configurations were studied. The configuration that gave the highest indicated efficiency has a leading pocket with a leading deep recess, two spark plugs located circumferentially on the symmetry plane (one after the minor axis and the other before), a compression ratio of 9.5, and an anti-quench feature on the trailing flank.

A simplified model for multicomponent droplet vaporization is developed and implemented in a multidimensional model for flows, sprays and combustion in engines. The model is applied to study the vaporization characteristics of a multicomponent droplet under Diesel conditions, the distribution of the vapor components in a Diesel spray and the distribution of the components in a Diesel engine. It is shown that for typical warm Diesel engine operating conditions, the droplets vaporize sufficiently rapidly that the stratification of the different components in the spray is not significant. However, under engine starting conditions and, in particular, cold starting conditions, there is a significant stratification of the different components of the fuel. When the species are stratified, the heavier and slower vaporizing components are predicted to be on the periphery of the spray envelope. However, these components also take longer to reach there.

A closed-circuit television technique has been developed for the real time viewing and recording of combustion and related processes in internal combustion engines. The technique has been applied to a transparent piston, transparent head engine, and shadowgraphs of combustion chamber events have been observed and recorded. The technique is particularly suited for the study of changes in the combustion process due to variations of engine parameters such as mixture ratio, load, speed, spark timing, injection initiation, etc., since the changes can be observed and recorded at the same time that they occur. A brief and qualitative study of flame and pressure cyclic variations is reported and discussed as an example of an application for which the television technique is particularly suited.

The combustion characteristics of three gaseous fuels (hydrogen, methane and ethane) in a direct-injection stratified-charge single-cylinder engine with a centered square head-cup operated at 800 rpm (compression ratio = 10.8, squish ratio = 75%, nominal swirl ratio = 4) were studied to assess the extent to which the combustion is controlled by turbulent mixing, laminar mixing and chemical kinetics. The injection of gaseous fuels was via a Ford AFI injector, originally designed for the air-forced injection of liquid fuel. Pressure measurements in the engine cylinder and in the injector body, coupled with optical measurements of the injector poppet lift and shadowgraph images of the fuel jets provided both quantitative and qualitative information about the in-cylinder processes. To make the cases comparable, the total momentum of the fuel jets and the total heat released by the three fuels was kept the same (equivalence ratio = 0.316, 0.363, 0.329 for H2, CH4 and C2H6, respectively).

Laser Doppler velocimetry was used to make cycle-resolved velocity and turbulence measurements under motoring and firing conditions in a ported homogeneous charge S.I. engine. The engine had a flat pancake chamber with a compression ratio of 7.5. In one study, the effect of the intake velocity on TDC turbulence intensity was measured at 600, 1200, and 1800 rpm with three different intake flow rates at each speed. The TDC swirl ratio ranged from 2 to 6. The TDC turbulence intensities were found to be relatively insensitive to the intake velocity, and tended to scale more strongly with engine speed. For the combustion measurements, the engine was operated at 600, 1200, and 2400 rpm on stoichiometric and lean propane-air mixtures. Velocity measurements were made in swirling and non-swirling flows at several spatial locations on the midplane of the clearance height. The TDC swirl ratio was about 4. The measurements were made ahead, through, and behind the flame.

Recent experimental results have shown that the penetration length of the liquid phase in a Diesel spray under normal operating conditions is relatively short compared to the penetration length of the overall jet. In addition, the results indicate that, for a significant fraction of the injection duration, the mass and volume of the injected fuel that is in the liquid phase is relatively small compared to the total volume and mass of fuel injected. Based on these considerations, a Virtual Liquid Source (VLS) model for Diesel sprays has been developed which treats the liquid region of the spray as a source of mass, momentum and energy without directly computing the liquid phase. The penetration length of the liquid phase along the axis of injection is obtained from recent measurements.

The objective of this work was to establish whether two detergent-type additives(A and B) influence the drop size and evaporation of two Diesel fuels (1 and 2) under Diesel engine conditions. Two experiments were performed: visualization of liquid and vapor fuel by the exciplex technique in a motored single-cylinder engine and measurement of the Sauter mean diameter, total drop cross sectional area and total drop volume by laser diffraction in a spray chamber. The same Diesel injector and pump system were used in the two experiments. The engine tests were carried out using a high aromatic content fuel (1) particularly suited for the exciplex studies. These studies showed that additive A yielded a lower vapor signal than additive B, which in turn gave a lower vapor signal than untreated fuel. Spray chamber results were obtained for both fuel 1 and 2. Additive A reduced the evaporation of fuel 1 whereas additive B gave a smaller and less consistent affect.

A two-color Particle Image Velocimetry (PIV) technique has been applied for the first time to a firing, production, three-cylinder, two-stroke, direct-injection stratified-charge engine operated under realistic conditions. In comparison to single color PIV, two-color PIV can resolve the directional ambiguity of the velocity by cross-correlating two digitized photographic images of a particle-seeded flow field, acquired sequentially at two different light wavelengths. Such an approach is essential in complex, a priori unknown, flow fields, such as those of most I.C. engines. To gain optical access to the combustion chamber, the engine head was equipped with two optical windows in such a way that its original geometry was practically undisturbed. Although the field of view was relatively small, it covered a critical area of the combustion chamber. The measurements were made in the plane perpendicular to the engine longitudinal axis, within the crank angle range of 70 to 10 degrees BTDC.

A second effort is reported to reproduce the distribution of fuel from a pulsating hollow-cone liquid-only poppet injector measured by the planar exciplex technique within the head cup of a motored ported single-cylinder engine operated at 1600 rpm with high swirl and a squish ratio of 75%. The injector, cup and cylinder were coaxial. The engine flowfield without injection had previously been characterized by LDV and PIV and so had been the injector and its spray in constant pressure environments. In a previous effort, the injector was assume to generate drop and the computed collapse of the spray was found to be too slow. In this work, the injector is assumed to generate liquid sheets that change shape and produce drops from their leading edges and surfaces as they propagate through the gas.

The combustion chamber pressure computed with a three-dimensional model is compared with the measured one in a rotary engine fueled with mixtures of natural gas and air. The rotary engine has a rotor displacement of 654 cm3, a compression ratio of 9.4 and uses 2 ignition sparks. The model incorporates a k-ϵ submodel for turbulence, wall function submodels for turbulent wall boundary layer transport, and a hybrid laminar/mixing controlled submodel for species conversion and energy release. Nine cases are considered that cover a wide range of engine operating conditions: rpm of 2503-5798, volumetric efficiency of 35.7-100.5% and equivalence ratio of 0.59-1.15. In all cases the computed and measured pressures agree within 12%.

Computations are reported of transient axisymmetric pulsating and evaporating sprays that account also for drop collisions and coalescence. It is found that, for the same upstream and gas conditions, pulsating injections result in smaller drops than continuous injections. The difference is particularly marked at high gas densities and is due to the inhibition of collisions and coalesce of drops generated by the gas gap in between the pulses. However, the tip penetration rates are not markedly different for continuous and pulsating injections. For transient evaporating sprays it is found that all drops except the largest evaporate within a well defined distance from the injector. Beyond this distance only vaporized liquid and entrained gas continue the penetration. For engine applications the length of the liquid core is found to be of the order of centimeters and sensitive to conditions. In particular it decreases with increasing injection pressure, gas temperature, and gas density.

Laser Doppler velocimetry has been used to make cycle-resolved velocity and turbulence measurements in a homogeneous-charge, spark-ignition engine. The engine had a ported intake and disc-shaped chamber with a compression ratio of 7.5 to 1. It was operated at a speed of 1200 rpm and with a TDC swirl number of 4. A stoichiometric propane-air mixture was used, and ignition was near the wall. Measurements of the tangential velocity component were made in both firing and non-firing cycles at nine spatial locations along a radius 180 degrees downstream of the spark. The radial velocity component was also measured at four of the locations. All measurements were made in the center of the clearance height. Tangential component measurements were made as close as 0.5mm from the cylinder wall, and the radial component was measured as close as 1.5mm from the wall.

In a previous study, the authors compared the fuel-air mixing characteristics of gas jets and sprays in Diesel engine environments in the absence of combustion. A three-dimensional model for flows and sprays was used. It was shown that mixing was slower in gas jets relative to fast-evaporating sprays. In this study, which is an extension of the previous one, the direct-injection of gasesous methane, gaseous tetradecane and liquid tetradecane are studied using the same three-dimensional model. This study concentrates on combustion. It is shown that the fuel-air mixing rate and hence the burning rate are initially slower with gas injection.

Simultaneous fuel distribution images (by shadowgraph and laser-induced fluorescence) and cylinder pressure measurements are reported for a combusting stratified-charge engine with a square cup in the head at 800 RPM and light load for two spark locations with and without swirl. Air-assisted direct-injection occurred from 130°-150° after bottom dead center (ABDC) and ignition was at 148° ABDC. The engine is ported and injection and combustion take place every 6th cycle. The complicated interaction of the squish, fuel/air jet, square cup, spark plug geometry and weak tumble gives rise to a weak crossflow toward the intake side of the engine with no swirl, but toward the exhaust side in the presence of strong swirl, skewing the spray slightly to that side.

Results are presented of 3-D computations of direct injection of gaseous methane and of liquid tetradecane through a multi-hole injector into a Diesel engine. The study focusses on the distribution of fuel/air ratio within the resulting gas and spray jets under typical Diesel conditions prior to ignition. It is shown that for a significant time after start of injection, the fraction of the vapor fuel which is in richer-than-flammable mixtures is greater in gas jets than in sprays. For methane injection, it is also shown that changing some of the flow conditions in the engine or going to a poppet-type injector, does not result in improved mixing. An explanation of these results is provided also through an analysis of the self-similar gas jet and 2-D computations of gas and spray jets into constant pressure gas. A scaling for time and axial distance in the self-similar gas jet also clarifies the results.

Efforts are reported to reproduce the distribution of liquid and vapor fuel from a pulsating hollow-cone liquid-only injector measured by the planar exciplex technique within the head cup of a motored ported single-cylinder engine operated at 1600 rpm with high swirl and a squish ratio of 75%. The injector, cup and cylinder were coaxial. The measurements show that shortly after the beginning of the injection the maximum liquid and vapor fuel concentrations are along the axis but also that the spray achieves substantial radial and axial penetrations. The engine flowfield without injection had previously been characterized by LDV and PIV and so had been the injector and its spray in constant pressure environments so that little arbitrariness was left in reproducing the spray in the engine. Two spray models were used. In one the large drops produced by the break up of the liquid sheet were introduced into the numerical field at the injector exit nearly with the poppet seat angle.

Results of experiments performed on a direct-injection two-stroke engine using an air-assisted injector are presented. Pressure measurements in both the engine cylinder and injector body coupled with backlit photographs of the spray provide a qualitative understanding of the spray dynamics from the oscillating poppet system. The temporal evolution of the spatial distribution of both liquid and vapor fuel were measured within the cylinder using the Exciplex technique with a new dopant which is suitable for tracing gasoline. However, a temperature dependence of the vapor phase fluorescence was found that limits the direct quantitative interpretation of the images. Investigation of a number of realizations of the vapor field at a time typical of ignition for a stratified-charge engine shows a high degree of cycle to cycle variability with some cycles exhibiting a high level of charge stratification.

Interactions between the jets in a multi-hole injector and between the jet and the wall may affect the fuel-air mixing processes in a direct-injection Diesel engine. These interactions are the subject of the investigation in this work. It is known that in the case of free jets, for a given total mass and momentum flow rate, increasing the number of holes would result in an increase in the mixing rate. In the case of a multi-hole injector in an engine, however, if the number of holes are increased beyond an optimum value, the interaction between the jets themselves may result in a reduced mixing. In the limit of increasing the number of holes, a hollow-cone jet would result. The fuel-air mixing in the hollow-cone jet is shown to be slower than in a multi-hole injector with an optimum number of holes.

Cycle-resolved LDV measurements of tangential and radial velocities were made in a ported engine within four piston cups. One cup was centered circular, one off-center circular, one centered square and one off-center square. The engine speed was 1200 rpm, the compression ratio 10.8, the squish area 75% and the TDC swirl ratio 4 for a pancake chamber. The velocity measurements were made at four depths in two axial sections. Near TDC in the centered circular cup, the profile of the ensemble-averaged tangential velocity tends to solid body with a swirl ratio of 12.5. In the centered square cup, the same velocity tends to solid-body profile along the short section and to top-hat profile along the outer part of the long section. The corresponding TDC swirl ratios are 11.3 and 5.5 due to mass conservation. The trends are similar but more complex in the off-center circular and square cups. In the centered circular cup, the swirl center is close to the cylinder axis near TDC.