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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.

A three-dimensional model is used to compute the flow,sprays and combustion in a stratified-charge rotary engine. Wall temperatures estimated from available measurements are used as boundary conditions for the energy equation. The computations provide local and instantaneous heat fluxes on the rotor and the rotor housing. The instantaneous heat fluxes are integrated in time over one cycle of the rotor to obtain estimates of local cycle averaged heat flux through the rotor and the rotor housing. These are then used as boundary conditions in a thermal analysis of the rotor and rotor housing with known coolant-side flow rates and heat transfer coefficients. The thermal analysis is done using a finite-element three-dimensional code which provides updated estimates of the rotor and rotor housing wall temperatures. These wall temperatures agree within ±20°C of the measured wall temperatures.

A three-dimensional combustion model for a direct-injection stratified-charge rotary engine is used to identify modifications to the engine that should lead to better indicated efficiency. The engine has a single spark plug positioned alongside a single-hole pilot injector in a cavity located after the minor axis and a five-hole main injector that is located before the minor axis. It is predicted that a second ignition source located upstream of the main injector will lead to an increase in indicated efficiency of 6-8% if it ignites the mixture consistently. The computations were made at high and low engine speeds and loads, covering a significant part of the practical operating range of the engine. It is also predicted that the gain in efficiency of the engine with two ignition sources would be 7-10%, instead of 6-8%, if a two-hole pilot injector is also used instead of the one-hole pilot.

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.

Computations of combustion in a stratified-charge rotary engine are presented. A three-dimensional model for flows, sprays and combustion which includes the ignition cavity of the engine is used to make these computations. The geometric complexity of the cavity and its coupling with the main chamber is handled by using an unsteady generalized curvilinear coordinate system. The grid is generated using an algebraic grid generator in the main chamber and by solving an elliptic equation in the cavity. Computations of the flows in the cavity are presented for different arrangements of the pilot injector and spark plug and for different timings and fuel injection rates from pilot and main injectors. The dominant feature of the flowfield in the cavity is shown to be the presence of a vortex, induced by the flow in the main chamber, which controls the distribution of the fuel and also the burning rate in the cavity.

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.

Results of comparisons of computed and measured soot and NO in a direct-injection Diesel engine are presented. The computations are carried out using a three-dimensional model for flows, sprays and combustion in Diesel engines. Autoignition of the Diesel spray is modeled using an equation for a progress variable which measures the local and instantaneous tendency of the fuel to autoignite. High temperature chemistry is modeled using a local chemical equilibrium model coupled to a combination of laminar kinetic and turbulent characteristic times. Soot formation is kinetically controlled and soot oxidation is represented by a model which has a combination of laminar kinetic and turbulent mixing times. Soot oxidation appears to be controlled near top-dead-center by mixing and by kinetics as the exhaust is approached. NO is modeled using the Zeldovich mechanism.

Studies are reported of stratified-charge combustion in rotary engines. They were performed with a three-dimensional model that computes intake, compression, liquid fuel injection, combustion, expansion, and exhaust. Comparisons are shown of computed and measured chamber pressures for two engines and seven conditions. They are the first comparisons of three-dimensional computations for rotary engines. The agreement is adequate for the purpose of interpreting the main features of the combustion flowfield. Then two subjects are considered: the mixing of injected-fuel and air, and the pressure non-uniformity within the combustion chamber. It is found that the TDC turbulence diffusivity of rotary engines in general is smaller than in corresponding reciprocating engines because of the longer time between intake and TDC. The pressure non-uniformity is shown to be caused by large fluid acceleration around TDC.

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.

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%.