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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.

The objective of this study is to characterize the operation of an air-assisted fuel injector. This characterization involves four sets of tests: fuel and air flow calibration; instantaneous measurements of fuel and air solenoid signals, internal pressure in the injector, and poppet lift; photographs of the spray; and droplet sizing. The injector poppet was designed to form a spray of 80° included angle. Nitrogen, instead of air, was used to assist the injection of unleaded gasoline into steady, compressed nitrogen at room temperature. The following conditions were used: nominal fuel flow rates of 10, 20, and 30 mm3/injection; spray chamber pressures of 0.1, 0.169, and 0.445 MPa; and nominal injections per minute (IPM) of 1600 and 3000. Results showed a linear increase in total fuel mass supplied to the injector as fuel solenoid pulse width was increased, except at the highest IPM and chamber pressure when the total fuel mass tended to level off.

Recent measurements by of gas intake flows and exhaust pressure in a motored, ported, single-cylinder engine with strong swirl and roll have been used as boundary conditions to a three-dimensional, transient computer simulation of the flow within the cylinder. For each condition, the calculation is continued over several engine cycles until the periodic solution is obtained. The computed TDC tangential velocity and turbulence intensity are then compared with measured ones. A technique is described to evaluate scavenging efficiency, the fraction of charge that remains in the cylinder over later cycles and the degree of mixedness of fresh and residual charge. For this motored ported engine, it is found that the scavenging efficiency is very low (19.4% at 1200 RPM) and the inflow from the exhaust ports is very significant. For practical ported engines with combustion, the scavenging efficiency is much higher but the inflows from exhaust ports are still expected to be significant.

A three-dimensional model for a direct injection stratified-charge rotary engine has been employed to study two modifications to the pocket geometry of the engine. In one modification, a pocket is located towards the leading edge of the rotor and is shown to produce recirculation within the pocket and faster burning. In the second modification, a two pocket rotor with two injectors and two spark plugs is studied. It appears that this should result in better utilization of the chamber air. It also appears that both modifications rhould result in higher efficiency of the direct-injected stratifiedcharge rotary engine. However extensive computations are required before a final conclusion is reached and before specific recommendations can be made.

For practical, extensive 3-D computations for engine improvements, each physical submodel needs to be the simplest that is compatible with the accuracy of all other physical submodels and of the numerics. The addition of one progress variable controlled by one Arrhenius term is shown to be adequate to reproduce Diesel ignition delay in 2-D and 3-D computations. The rest of the model is that used for years by the authors to optimize combustion in reciprocating and rotary engines with premixed and non-premixed charges, including all of its model constants. This minimal Diesel autoignition submodel reproduces well trends and magnitudes of ignition delay versus chamber temperature and pressure. As in experiments, it is found that multiple ignition sources develop in rapid succession at various locations around the fuel spray after the first ignition event.

The exciplex fluorescence technique has been used to separately visualize liquid and vapor phase fuel in engines since its development by Melton. However, as a fluorescence technique it has the potential to be quantitative and the underlying assumptions have been outlined by Melton. An initial quantitative application of the TMPD/naphthalene system, based on these assumptions, applied to a hollow-cone spray in a two-stroke engine, indicated that it substantially over-estimates the concentration of fuel vapor about TDC. The reasons for the discrepancy were investigated and it was concluded that a major factor is the effect of temperature on the photophysics of the species involved. Thus the absorption spectra of the exciplex dopants were determined at temperatures up to 700 K. These experiments showed that the increase in absorption with temperature above 500 K is responsible for the failure of the earlier calibration.

Results are presented of two-dimensional computations of air-assist fuel injection into engines with bowl-in-piston and bowl-in-head, with and without swirl and for early and late injection but without combustion. The general finding is that swirl tends to destroy the head vortex of the air/fuel jet and results in a faster collapse of the spray cone toward its axis. Faster collapse is also promoted by high density of the chamber gas (e.g. late injection) and bowl-in-head design (limited availability of chamber gas around the spray, presence of walls and delayed influence of squish by the injector). With enhanced collapse, fuel-rich regions are formed around the axis and away from the injector. With reduced collapse, the radial distribution of the fuel is more uniform. Thus swirl tends to lead to both slower vaporization and richer vapor mixtures. Also, with strong swirl the rich mixtures tend to end up by the injector; without swirl, by the piston.

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.

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.

Engine-out, cold-start (from 20°C) UHC emissions from a contemporary 2.0 4-cylinder engine with swirl control were measured with FID and FT-IR. The steady-state, end of test operation was 1500 rpm, 2.6 bar BMEP (25% load) and stoichiometric mixture. Four fuel systems were employed pintle-type port-injected gasoline, air-forced port-injected gasoline, port-injected propane, and premixed propane. These fuel systems were chosen to separate effects of fuel atomization, vaporization, and fuel-air mixing. Each system was optimized with respect to injector targeting, injection timing, mixture enrichment, and spark advance. Open-valve injection timing increased UHC emissions more with the pintle-type injector than with the air-forced, system. UHC emissions with propane injection were minimized with open valve injection.

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.

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).

Combustion in a divided-chamber, stratified-charge engine is considered and flame and pressure results obtained with a two-dimensional, unsteady model are compared with corresponding engine data. The model is applied to eight engine conditions differing in speed, load and size of the prechamber orifice. The model employs one overall chemical reaction rate, the k-ε representation of turbulence, and a wall heat loss proportional to the heat release. The computed results are shown to be in good agreement with the experimental ones in spite of the complexity of the problem and the early stages of detailed model validation studies. They are also shown to compare somewhat better than earlier ones obtained with an ad-hoc jet turbulence model. Both studies prove the importance of the prechamber jet to the overall combustion process for the particular engine investigated.

Atomization and full-cone sprays from single cylindrical orifices are considered. The following subjects are reviewed: the structure of the breakup region; the structure of the far field; modern models that, given the outcome of the breakup process, compute the steady and transient of sprays; some comparisons with detailed measurements; and some practical applications. The following conclusions are reached: the spray breakup and the development regions are the most relevant in engine applications; the inner structure of the breakup region is still largely unknown; two- and three-dimensional spray models are available but remain mostly untested, particularly in their vaporization and combustion components, in part because of a lack of accurate measurements in controlled engine-type environments; engine applications of such models are, nonetheless, recommended for very valuable learning, interpretative, and exploratory studies, but not for predictions.

Two dimensional visualization of a pulsating, hollow-cone spray was performed in a motored, ported, high swirl, cup-in-head I.C. engine, using exciplex-forming dopants in the fuel, which produced spectrally separated fluorescence from the liquid and vapor phases. Illumination was by a laser sheet approximately 200 µm thick from a frequency tripled Nd:YAG laser, and image acquisition was by a 100 × 100 pixel diode array camera interfaced to a personal computer. Liquid and vapor phase fuel distributions are reported for engine speeds of 800 rpm and 1600 rpm, over a crankangle range spanning the injection event and subsequent evaporation and mixing. The beginning of injection was at 33° BTDC at 800 rpm and 47° BTDC at 1600 rpm. At 800 rpm, the spray angle is narrower than the 60° poppet angle, as expected from previous observations in a near-quiescent spray chamber.

A three-dimensional model for flows and combustion in reciprocating and rotary engines is applied to a direct-injection stratified-charge rotary engine to identify the main parameters that control its burning rate. It is concluded that the orientation of the six sprays of the main injector with respect to the air stream is important to enhance vaporization and the production of flammable mixture. In particular, no spray should be in the wake of any other spray. It was predicted that if such a condition is respected, the indicated efficiency would increase by some 6% at higher loads and 2% at lower loads. The computations led to the design of a new injector tip that has since yielded slightly better efficiency gains than predicted.

A three-dimensional combustion model of a direct-injection stratified-charge rotary engine is used to identify modifications that might lead to better indicated efficiency. The engine, which has a five-hole main injector and a pilot injector, is predicted to achieve better indicated efficiency if a two-hole ‘rabbit-ear’ pilot injector is used instead of its present single-hole pilot injector. This rabbit-ear arrangement is predicted to increase the surface area of the early flame (on account of better distribution of the fuel), and thereby result in an increased overall burning rate. Computations were made at high and low engine speeds and loads, encompassing the practical operating range. It is concluded that the modified pilot injector will increase indicated efficiency by about 5% within the computed operating range.

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 8 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. The velocity measurements were made at three spatial locations at the midpoint of the clearance height. Tests were made to determine whether the presence of the flame affected the accuracy of the velocity measurements. It was found that the ensemble-averaged mean velocity shows a small deviation, and the rms fluctuation intensity is significantly influenced, but the effects appear to be confined to the flame zone. Data rates were sufficiently high in the preflame and postflame regions to determine the velocity history in each cycle (cycle resolved).

The structure of turbulent flames was examined in a premixed-charge, spark-ignition ported engine using a three-dimensional visualization technique with 10 ns time resolution and 350 µm best spatial resolution. The engine had a pancake chamber, a compression ratio of 8, a TDC swirl number of 4 and was operated at 300, 1200 and 2400 rpm with stoichiometric and lean propane/air mixtures. The second and third harmonic beams of an Nd-YAG laser (532 nm and 355 nm), along with the two strongest beams (first Stokes (683 nm) and first anti-Stokes (436 nm)) from a hydrogen Raman shifter pumped by the second harmonic were used to create four parallel laser sheets each of less than 300 microns thickness. The laser sheets were passed through a transparent quartz ring in the cylinder head parallel to the piston top with vertical separations between successive sheets ranging from 1.5 to 0.9 mm.