Seong-Ho Jin

Experimental and Numerical Study of an Air Assisted Fuel Injector for a D.I.S.I. Engine

The transient behaviour of the fuel spray from an air assisted fuel injector has been investigated both numerically and experimentally in a Constant Volume Chamber (CVC) and an optical engine. This two phase injector is difficult to analyse numerically and experimentally because of the strong coupling between the gas and liquid phases. The gas driven atomization of liquid fuel involves liquid film formation, separation and break up and also liquid droplet coalescence, break up, splashing, bouncing, evaporation and collision. Furthermore, the liquid phase is the dominant phase in many regions within the injector. Experimental results are obtained by using Mie scattering, Laser Induced Fluorescence (LIF) and Laser Sheet Drop sizing (LSD) techniques. Computational results are obtained by using a mixed Lagrangian/Eulerian approach in a commercial Computational Fluid Dynamic (CFD) code. Injector rig results show a good atomization of the spray with low spray width and penetration and Sauter Mean Diameters SMD) of droplets of order 10 μm. Engine results show a spray with a relatively low penetration producing liquid fuel and vapour fuel concentrations close to the central location of the injector and spark plug for stratified, lean mode of operation. Imaging of this injector operating inside an engine confirms the overall design approach for stratified operation.

An experimental study of the spray from an air-assisted direct fuel injector

The transient behaviour of the fuel spray from an air-assisted direct-injection spark ignition (DISI) fuel injector has been investigated experimentally in a constant-volume chamber. As the chamber and injection pressures were varied, ensemble-averaged planar images of the laser-induced fluorescence (LIF) and Mie scattering from the spray were obtained to measure the Sauter mean diameter (SMD) using the laser sheet drop-sizing (LSD) technique. The root mean square (r.m.s.) SMD was also calculated by combination of the r.m.s. LIF and r.m.s. Mie scattering signals. The effect of the injection and chamber pressures and the ambient air density on the SMD, spray tip penetration, and dispersion of the air-assisted fuel injector are determined. In keeping with recent numerical studies by the group, vortex structures appear to be shed from the injector tip in back-illuminated images, indicating that the air and liquid motion are strongly coupled. These results also show that the spray penetration and SMD vary significantly with injection and chamber density, and scalings of the sprays overall SMD and penetration are proposed that achieve reasonable clustering in the experimental results.

Experimental and numerical study of a spark ignition engine with air-assisted direct injection

Abstract An experimental and numerical study of the spray from an air-assisted fuel injector in a direct-injection spark ignition (DISI) engine is presented. The experiments are performed using ultraviolet laser diagnostics in a motoring optical engine that is a DISI variant of a production port-fuel-injected engine. Non-optical single-cylinder firing engine results of experiments and simulations are also presented. Recent related work by the present authors has shown that, under design conditions, the air-assisted injector exhibits strong coupling between the liquid and gas phases. It results in a filled-in conical spray of relatively fine atomization and low penetration, with liquid and vapour fuel concentrations close to the centrally located injector and spark plug, as required for lean stratified operation. This paper shows the strong effect of increasing the chamber temperature on spray evaporation and penetration. This observed temperature effect shows that spray evaporation should vary significantly during cold start. Exhaust gas recirculation (EGR) may also have a beneficial effect on DISI engine performance through enhanced spray evaporation, although this is difficult to verify experimentally. If true, this effect of EGR is a separate mechanism to the known beneficial effects of EGR in air-assisted DISI engines.

Experimental and numerical analysis of engine gas exchange, combustion and heat transfer during warm-up

This paper presents experimental and computational results obtained on an in line, six cylinder, naturally aspirated, gasoline engine. Steady state measurements were first collected for a wide range of cam and spark timings versus throttle position and engine speed at part and full load. Simulations were performed by using an engine thermo-fluid model. The model was validated with measured steady state air and fuel flow rates and indicated and brake mean effective pressures. The model provides satisfactory accuracy and demonstrates the ability of the approach to produce fairly accurate steady state maps of BMEP and BSFC. However, results show that three major areas still need development especially at low loads, namely combustion, heat transfer and friction modeling, impacting respectively on IMEP and FMEP computations. Satisfactory measurement of small IMEP and derivation of FMEP at low loads is also a major issue. Measurements of fuel consumption were then collected during warm up for different configurations of the cooling system, with a standard mechanical water pump (MWP) and an electrical water pump (EWP), at a constant BMEP and engine speed. Simulations were performed by using the previous model to compute IMEP and FMEP. Modeling friction during warm-up, when temperatures of head metal, block metal, coolant and oil are well below hot steady values and decoupled to some extent (split or no flow coolant tests) proves to be challenging. Computational results complement the experimental data, demonstrating the utility of the integrated approach in improving the design of the cooling system for faster warm-up.