Search Results

This study brings to forefront the analysis capability of CFD for the oil-cooling of an Electric-Motor (E-Motor) powering an automobile. With the rapid increase in electrically powered vehicle, there is an increasing need in the CFD modeling community to perform virtual simulations of the E-Motors to determine the viability of the designs and their performance capabilities. The thermal predictions are extremely vital as they have tremendous impact on the design, spacing and sizes of these motors. In this paper, with the Simerics, Inc. software, Simerics-MP+®, a complete three dimensional CFD with conjugate heat transfer CHT model of an Electric Motor, including all the important parts like the windings, rotor and stator laminate, endrings etc. is created. The multiphase Volume of Fluid (VOF) approach is used to model the oil flow inside this motor.

Large-eddy simulations (LES) of a motoring single-cylinder engine with transparent combustion chamber (TCC-II) are carried out using a commercially available computer code, CONVERGE. Numerical predictions are compared with high-speed particle image velocimetry (PIV) measurements. Predictions of two spatial discretization schemes, namely, numerically stabilized central difference scheme (CDS) and fully upwind scheme are compared. Four different subgrid scale (SGS) models; a non-eddy viscosity dynamic structure turbulence (DST) model of Pomraning and Rutland, one-equation eddy-viscosity (1-Eqn) model of Menon et al., a zeroequation eddy-viscosity model of Vreman, and the zeroequation standard Smagorinsky model are employed on two different grid configurations. Additionally, simulations are also performed by deactivating the LES SGS models. It is found that the predictions when using the numerically stabilized CDS are significantly better than using the fully upwind scheme.

A primary goal of large eddy simulation, LES, is to capture in-cylinder cycle-to-cycle variability, CCV. This is a first step to assess the efficacy of 35 consecutive computed motored cycles to capture the kinetic energy in the TCC-III engine. This includes both the intra-cycle production and dissipation as well as the kinetic energy CCV. The approach is to sample and compare the simulated three-dimensional velocity equivalently to the available two-component two-dimensional PIV velocity measurements. The volume-averaged scale-resolved kinetic energy from the LES is sampled in three slabs, which are volumes equal to the two axial and one azimuthal PIV fields-of-view and laser sheet thickness. Prior to the comparison, the effects of sampling a cutting plane versus a slab and slabs of different thicknesses are assessed. The effects of sampling only two components and three discrete planar regions is assessed.

An Arrhenius combustion model (chemically controlled model) with a spark-energy deposition model having a moving spherical ignition source in the Converge CFD code is validated with a single-cylinder spray-guided SIDI engine at idle-like lean-burn operating conditions with both single- and double-pulse fuel injection. It was found that a fine mesh is required for accurate solving of "laminar-flame" like reaction front propagation. A reduced chemistry mechanism for iso-octane is used as gasoline surrogate. The effects of spark advance were studied by the simulation and experiment. The results show that this modeling approach can provide reasonable predictions for the spray-guided SIDI engine with single- and double-pulse injections.

Combustion simulation is an effective tool in overcoming the issues associated with gasoline HCCI engines, controlling ignition timing and extending the operating range. The research discussed in this paper commenced by optimizing the reaction mechanism from the perspective of ignition delay using the genetic algorithm (GA) method. Simulations employing the optimized reaction mechanism were then able to more accurately reproduce the ignition timing of iso-octane and primary reference fuels (PRF). Ignition times obtained from simulations showed excellent correlation with ignition times measured using these fuels in shock tube experiments, and in engines with both homogeneous and non-homogeneous fuel distributions. The use of the PRF mechanism for gasoline with an equivalent octane number enables excellent reproduction of ignition timing even when EGR is employed.

This paper presents two factors for improving the performance and emissions characteristics in HCCI diesel combustion, one is reducing compression ratio and another is changing the injector position. In a previous study, it was shown that HCCI diesel combustion could be realized by utilizing a hollow-cone spray with normal injection pressure. However there remained two major problems of engine instability and increase in BSFC (decrease in brake thermal efficiency). By reducing the compression ratio from 18.8 to 16.8, the engine stability was much improved to the level of conventional diesel combustion and the increase in BSFC became almost half, which was mainly due to the change of combustion phasing. In addition to this, application of 5 mm inside position of the injector realized almost no penalty of BSFC at higher load condition.

To model sprays from pintle type nozzles with large hollow cone angle and high injection pressure, the correct flow field in the near region must be predicted. A new model was implemented in KIVA-3V code, which adopts the theory of steady gas jet to correct the relative velocities between the drop and gas phases, based on the existence of quasi-steady part of the conical spray and an assumption of equivalent gas jet. Accordingly, the structure of the sprays is defined into three parts: 1. initial part that the gas phase velocity is set to the assumed gas injection velocity; 2. quasi-steady part where the component of velocity in the symmetric line direction of the spray is corrected; 3. stagnation part which is left unchanged. This new model is referred to as the Relative Velocity Correction (RVC) model, and is a set of empirical equations that calculate the sectional distribution of the gas-phase velocity along the symmetric line of the sprays.

A relative velocity correction model (RVC), combined with the drop tracing system and spherical coordinate transformation, was developed and implemented in KIVA-3V code to yield grid-independent results for the spray simulations, especially for 3-D cases. The model applies the theory of steady turbulent jet flow to obtain sectional distribution of the gas-phase velocity along the spray axial in near region, which is used to correct the relative velocity between the drop and gas phases. The computed results were compared with the experimental data for both single-hole and three-hole fuel injections, including the spray tip penetrations and the spray images. The comparison shows that the RVC model performed well for all the cases.

Three-dimensional time-dependent calculations are performed to investigate the compressible turbulent flow about a train passing through a single-track tunnel. The “snapper” algorithm in KIVA-3 is used to allow the train to pass through the stationary tunnel mesh. Actual train geometry is simplified considerably. The length of the train/tunnel as well as the speed of the train is considered to investigate their effects on the train-tunnel interaction. In an effort to understand the whole process of the train-tunnel aerodynamic interaction, the formation and propagation of the pressure waves, the radiation and reflection of the waves at the tunnel portals and the histories of aerodynamic forces on the train are studied. The experimental results compare well with the computational data.

Three-dimensional computations are performed to investigate the scavenging characteristics of poppet-valved two-stroke engines. The new subroutines are developed to handle various valve shrouds. Visualization of scavenging flow on a modified two-stroke transparent cylinder engine is used for validation and compared well in flow pattern. The flows in engines with different configurations are simulated at a speed of 5000 r/min. The stroke bore/ratio and valve arrangements were considered to investigate their effects on the scavenging flows. Additionally, valve timing and boost pressure have also been studied. The results show that stroke/bore ratio of 0.4 to 0.6, shroud angle of 69° to 108°, turn angle of shroud of 18° to 28°, average tumble ratio of 1.2-1.6 were found to be the optimum range for effective scavenging.

Observations of the scavenging flow field have been made in a modified poppet-valved two-stroke engine with a transparent cylinder. Four kinds of cylinder heads with different port configuration were created to analyze their effects on the scavenging flow and develop new scavenging concepts. A mineral oil fog discharge system was used to visualize the air flow during the scavenging process. All of the images were recorded by a high speed video camera which show the development of the scavenging processes and clearly indicate the scavenging jet structure, the tumble pattern and the location of re-circulation regions. The analyses allow us to judge the quality of the scavenging processes. The small changes in port geometry could significantly affect the scavenging flow. Tumble as well as swirl should be considered as main means to organize the scavenging flow in order to avoid short-circuiting losses and create condition favorable to combustion.

A new type direct-injection stratified-charge combustion system for gasoline engines is developed by the authors. In the system, gasoline is directly injected into a cylinder near the end of compression stroke by a nozzle with the injection holes unequally spaced on its tip. The angles among sprays in the vicinity of spark plug are small, and become larger downstream along the direction of air swirl motion. Therefore the circularly concentration stratification form rich to lean of air-fuel mixture is mechanically realized to ensure the reliable ignition and smooth flame propagation in the inhomogeneous mixture after sparking. The selection of main parameters of the system, the performance and the combustion characteristics of the engine after optimization of those parameters are introduced in detail in this paper.

A simple diaphragm injection carburettor (DIC) is developed and patented by the author in the paper. The principle is that, as the function of the diaphragm mechanism, the pressure difference between two sides of the metering hole equals the vacuum of the Venturi, so it can realize the pressurized fuel metering, by the fuel metering hole and vacuum from the Venturi, and fuel injection. The fuel is injected into the feed port and mixes with the small fraction of air through the port, the main port of fresh air from the crankcase is injected to the cylinder with the scavenging organized so that a separating layer is created between the exhaust and feed port, it can substantially reduce short-circuit. According to the characteristics of low short-circuit at low delivery ratio, the low load fuel supply system of conventional carburettor is preserved and combined with DIC which functions at high load operation.

Proper fuel supply system is the crux to realize the stratified scavenging for small type of two-stroke gasoline engine. A simple and effective diaphragm fuel injection system (DFI) is developed in the paper, which mainly consists of diaphragm pump and injector, the DFI utilizes the crankcase pressure which reflects the inlet flow rate to meter and inject fuel. As low short-circuit at low load operation, stratified scavenging seems not necessary, so the conventional carburetor is preserved to function at low load. This makes the whole fuel system simple and effective. The paper describes the operation principle of the DFI, and results of test on a 30cm3 modified engine are also presented, including the performance of fuel supply and contrast of complex engine performance with the original carbureted engine.