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The CFD code KIVA is used in conjunction with a one-dimensional wave action program to simulate exhaust blowdown, in a study of the scavenging and combustion at different loads and constant engine speed, in a single cylinder 4 valved 2-stroke engine configuration, using in-cylinder fuel injection. Two combustion chamber geometries -- a stepped head and a pentroof, were used in this study. The stepped head geometry has a combustion chamber recessed in the cylinder head, and contains the intake valves. The vertical intake port configuration provides a well developed reversed loop flow in the engine cylinder. The pentroof combustion chamber is similar to those used in current 4 stroke engines(1)*. The computational study focuses on the effects of injector orientation, and the subsequent interaction between the fuel spray and ‘loop swirl’ of air in the engine cylinder, and on the resulting combustion characteristics and exhaust emissions.

The CFD code KIVA has been applied to the simulation of the transient air-assisted fuel injection(AAFI) process, in which air and fuel at moderate pressures are mixed in an interior chamber of the injector before passing through a pintle valve into air at near ambient pressure in a cylinder. On passage through the pintle valve fuel is atomised. Because of the small dimensions of the flow passages within the injector, a very fine computational grid structure is used to accurately resolve the flow behaviour. Adopting an axisymmetric grid structure enables symmetry to be exploited. The computational results are validated with experimental data for fuel jet penetration and spread with time, obtained using Schlieren visualisation. The simulation of air blast atomisation in an engine cannot utilise the fine grid structure above because of the large computational resources required.

Hydraulically intensified medium pressure common rail (MPCR) electronic fuel injection systems are an attractive concept for heavy-duty diesel engine applications. They offer excellent packaging flexibility and thorough engine management system integration. Two different concepts were evaluated in this study. They are different in how the pressure generation and injection events are related. One used a direct principle, where the high-pressure generation and injection events occur simultaneously producing a near square injection rate profile. Another concept was based on an indirect principle, where potential energy (pressure) is first stored inside a hydraulic accumulator, and then released during injection, as a subsequent event. A falling rate shape is typically produced in this case. A unit pump, where the hydraulic intensifier is separated from the injector by a high-pressure line, and a unit injector design are considered for both concepts.

The in cylinder air motion, fuel air mixing, evaporation, combustion and exhaust emissions have been simulated for a four stroke direct injection gasoline engine using the KIVA II code. A strong controlled tumbling air motion was created in the cylinder, through a combination of a conventional pentroof four valve cylinder head, in conjunction with a piston having a stepped crown and offset combustion bowl. A range of injection strategies were employed to optimise combustion rate and exhaust emission (NOx and unburned hydrocarbons (fuel)), at two operating conditions - one with a stoichiometric air fuel mixture and the other with a lean mixture of 30:1 air/fuel ratio. Injection directed towards the piston bowl with a hollow cone jet, in a single pulse, has shown the best results regarding burned mass fraction and level of unburned HC. Fuel concentration, air motion, combustion characteristics and pollutants level are presented for lean and stoichiometric cases.

The process of autoignition in an internal combustion engine cylinder produces large amplitude high frequency gas pressure waves accompanied by significant increases in gas temperature and velocity, and as a consequence large convective heat fluxes to piston and cylinder surfaces. Extended exposure of these surfaces to autoignition, results in their damage through thermal fatigue, particularly in regions where small clearances between the piston and cylinder or cylinder head, lie in the path of the oscillatory gas pressure waves. The ability to predict spatial and temporal' variations in cylinder gas pressure, temperature and velocity during autoignition and hence obtain reasonable estimates of surface heat flux, makes it possible to assess levels of surface fatigue at critical zones of the piston and cylinder head, and hence improve their tolerance to autoignition.

The Computational Fluid Dynamics (CFD) Code KIVA II has been applied to model combustion pressure oscillations in the Indirect Injection Diesel Engine. These oscillations are attenuated and transmitted by the engine structure to the surroundings as noise. The computational model was used to evaluate changes in design and operating characteristics of an engine, and the effect of these on the intensity of gas pressure oscillation. The results in general corroborate the trends of published experimental measurements of combustion noise. A 40% increase in grid resolution showed minor changes in the magnitude of cylinder pressure oscillation and approximately 0.5ø crank angle phase advance in the oscillation cycle compared with the grid used for the results presented here.

In this paper the effect of in-cylinder crevices formed by the piston cylinder clearance, above the first ring, and the spark plug cavity, on the entrapment of unburned fuel air mixture during the late compression, expansion and exhaust phases of a spark ignition engine cycle, have been simulated using the Computational Fluid Dynamic (CFD) code KIVA II. Two methods of fuelling the engine have been considered, the first involving the carburetion of a homogeneous fuel air mixture, and the second an attempt to simulate the effects of manifold injection of fuel droplets into the cylinder. The simulation is operative over the whole four stroke engine cycle, and shows the efflux of trapped hydrocarbon from crevices during the late expansion and exhaust phases of the engine cycle.

The Computational Fluid Dynamics (CFD) code KIVA II has been applied to simulate the in-cylinder mean air motion (tumble) and turbulence levels in a motored 4-stroke single cylinder engine with pentroof combustion chamber geometry, having two inlet and two exhaust valves. In-cylinder flow during intake and compression strokes were simulated and a comparison between computational and experimental results were made. The mean turbulent kinetic energy and tumble ratio variation during the compression stroke obtained with CFD, have been compared with computational and experimental data from published literature. The simulation shows general similarity of flow structure and magnitude with published data on engines with similar geometry and initial flow conditions in the cylinder.

An electronically controlled Caterpillar single-cylinder oil test engine (SCOTE) was used to study diesel combustion. The SCOTE retains the port, combustion chamber, and injection geometry of the production six cylinder, 373 kW (500 hp) 3406E heavy-duty truck engine. The engine was equipped with an electronic unit injector and an electronically controlled common rail injector that is capable of multiple injections. An emissions investigation was carried out using a six-mode cycle simulation of the EPA Federal Transient Test Procedure. The results show that the SCOTE meets current EPA mandated emissions levels, despite the higher internal friction imposed by the single-cylinder configuration. NOx versus particulate trade-off curves were generated over a range of injection timings for each mode and results of heat release calculations were examined, giving insight into combustion phenomena in current “state of the art” heavy-duty diesel engines.