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Technical Paper

The Structure of Cavitation and its Effect on the Spray Pattern in a Single-Hole Diesel Nozzle

The structure and evolution of cavitation in a transparent scaled-up diesel nozzle having a hole perpendicular to the nozzle axis has been investigated using high-speed motion pictures, flash photography and stroboscopic visualization. Observations revealed that, at the inception stage, cavitation bubbles are dominantly seen in the vortices at the boundary layer shear flow and outside the separation zone. Cavitation bubbles grow intensively in the shear layer and develop into cloud-like coherent structures when viewed from the side of the nozzle. Shedding of the coherent cloud cavitation was observed. When the flow was increased further the cloud like cavitation bubbles developed into a large-scale coherent structure extending downstream of the hole. Under this condition the cavitation starts as a mainly glassy sheet at the entrance of the hole. Until this stage the spray appeared to be symmetric.
Technical Paper

Modelling of Gasoline and Ethanol Hollow-Cone Sprays Using OpenFOAM

Over the past few years, an open-source code called OpenFOAM has been becoming a promising CFD tool for multi-dimensional numerical simulations of internal combustion engines. The primary goal of the present study is to assess the feasibility of the code for computations of hollow-cone sprays discharged by an outward-opening pintle-type injector by simulating the experiments performed recently by Hemdal et al., (SAE 2009-01-1496) with gasoline and ethanol sprays under the following conditions: air temperature Tair = 295 or 350 K, air pressure pair = 6 bar, fuel temperature Tfuel = 243, or 295, or 320 K, and fuel injection pressure pinj = 50, or 125, or 200 bar. To simulate the experiments, a pintle injector model and the physical properties of gasoline were implemented in OpenFOAM. The flow field calculated using the pintle injector model is more realistic than that yielded by the default unit injector model normally used in OpenFOAM.
Technical Paper

Soot Evolution in Multiple Injection Diesel Flames

In order to meet future emission regulations, various new combustion concepts are being developed, several of which incorporate advanced diesel injection strategies, e.g. multiple injections, offering attractive potential benefits. In this study the effects of split injections on soot evolution in diesel flames were investigated in a series of flame experiments performed using a high pressure, high temperature (HP/HT) spray chamber and laser-induced incandescence apparatus to measure soot volume fractions. The focus was on split injections with varied dwell times preceded by a short pilot. The results, which were analyzed and compared to results from engine tests, show that net soot production can be decreased by applying an appropriate split injection strategy.
Technical Paper

The Role of Aerodynamics in the 1955 Le Mans Crash

In the 1955 Le Mans race the worst crash in motor racing history occurred and this accident would change the face of motor racing for decades. After the crash numerous investigations on the disaster were performed, and fifty years after some interesting books were launched on the subject. However, a number of key questions remain unsolved; and one open area is the influence of aerodynamics on the scenario, since the Mercedes-Benz 300 SLR involved in the crash was equipped with an air-brake and its influence on the accident is basically unknown. This work may be considered as a first attempt to establish CFD as a tool to aid in resolving aerodynamic aspects in motor sport accidents and in the present paper, CFD has been used to investigate the aerodynamics and estimate the drag and lift coefficients of the Mercedes-Benz 300 SLR used in the Le Mans race of 1955.
Technical Paper

Modelling Gasoline Spray-wall Interaction -a Review of Current Models

A literature survey was carried out to examine the advances in knowledge regarding spray impingement on surfaces over the last five years. Published experiments indicate that spray impingement is controlled by various spray parameters, surface conditions, and liquid properties. One disadvantage of the published results is that the experiments have mainly been conducted with water droplets or diesel fuel, often at atmospheric conditions. A sensitivity analysis was performed for one common impingement model. The purpose was to investigate how the model described different phenomena when different parameters were changed, including wall temperature, wall roughness and injection velocity of the spray. The model tested showed sensitivity to surface roughness, whereas changes in wall temperature only resulted in increased evaporation from the surface. The increase of injection velocity resulted in a decrease of fuel on the wall by 70%.
Technical Paper

Investigation of Spark Position Effects in a Small Pre-chamber on Ignition and Early Flame Propagation

Lean gas engines have a potential for a significant reduction in both fuel consumption and emission levels. The use of a small pre-chamber with controlled stoichiometric or rich mixture composition is an effective way to deal with ignition problems in such engines. A constant volume vessel equipped with a device for generation of turbulence of known quantities is used to study the operation of a cylindrical pre-chamber of 1% of the main chamber volume. Pressure was measured in the main chamber and Schlieren images of the flame initiation and propagation in the main chamber were recorded for all set-ups. The investigation of the pre-chamber is focused on the position of the spark within the pre-chamber. Spark locations close to the orifice and close to the opposite wall as well as in the middle of the pre-chamber were tested and flame evolution and pressure history were studied.
Technical Paper

Heat Release in the End-Gas Prior to Knock in Lean, Rich and Stoichiometric Mixtures With and Without EGR

SI Engine knock is caused by autoignition in the unburnt part of the mixture (end-gas) ahead of the propagating flame. Autoignition of the end-gas occurs when the temperature and pressure exceeds a critical limit when comparatively slow reactions-releasing moderate amounts of heat-transform into ignition and rapid heat release. In this paper the difference in the heat released in the end-gas-by low temperature chemistry-between lean, rich, stochiometric, and stoichiometric mixtures diluted with cooled EGR was examined by measuring the temperature in the end-gas with Dual Broadband Rotational CARS. The measured temperature history was compared with an isentropic temperature calculated from the cylinder pressure trace. The experimentally obtained values for knock onset were compared with results from a two-zone thermodynamic model including detailed chemistry modeling of the end-gas reactions.