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Fuel Injection System (FIS) research on injection pressure, timing control, and rate shaping, and studies on the modeling of injector nozzle flows and their effect on fuel spray characteristics are usually conducted separately. Only recently has the fuel injection and spraying process been studied as a complete system, i.e., including both the high-pressure fuel delivery and its effect on the nozzle flow characteristics, including nozzle cavitation. A methodology for coupling the fuel injection system and its effect on spray characteristics is presented here. The method is applied to an example case of a conventional pump-line-nozzle system. Mathematical models for characterizing the flows from the pump to the nozzle are formulated and solved using the Method of Characteristics and finite difference techniques. The nozzle internal flow is modeled using zero-dimensional flow models, in which the nozzle cavitation and its effect on the nozzle exit flow are accounted for.

Intake flow simulations were carried out for a prototype DISI engine using the standard k-ε model and the RNG k-ε model. The results were compared with PTV (transient water analog) measurements. The study was focused on low load operations with engine speed at 400 rev/min. Two cases were studied, a single intake case in which one intake port was blocked and a dual intake port case. In the computations, the results show that the standard k-ε model tends to produce higher turbulence levels when turbulence is generated and decays faster when turbulence dissipates. Different turbulence models predict almost the same flow structures. However, the effects of the turbulence model on the predicted tumble and swirl ratios are significant. The TKE distributions at BDC predicted by the two models are also different. The standard k-ε model seems to be more diffusive. Good agreements with PTV data were obtained in the single valve case with the RNG k-ε model.

A study was performed to correlate the Sauter Mean Diameter (SMD), NOx and particulate emissions of a direct injection diesel engine with various injection pressures and different nozzle geometry. The spray experiments and engine emission tests were conducted in parallel using the same fuel injection system and same operating conditions. With high speed photography and digital image analysis, a light extinction technique was used to obtain the spray characteristics which included spray tip penetration length, spray angle, and overall average SMD for the entire spray. The NOx and particulate emissions were acquired by running the tests on a fully instrumented Caterpillar 3406 heavy duty engine. Experimental results showed that for higher injection pressures, a smaller SMD was observed, i.e. a finer spray was obtained. For this case, a higher NOx and lower particulate resulted.

An image acquisition-and-processing camera system was developed for in-cylinder diagnostics of a single-cylinder heavy duty diesel engine. The engine was equipped with an electronically-controlled common-rail fuel injection system that allowed both single and split (multiple) injections to be studied. The imaging system uses an endoscope to acquire luminous flame images from the combustion chamber and ensures minimum modification to the engine geometry. The system also includes an optical linkage, an image intensifier, a CID camera, a frame grabber, control circuitry and a computer. Experiments include both single and split injection cases at 90 MPa and 45 MPa injection pressures at 3/4 load and 1600 rev/min with simulated turbocharging. For the single injection at high injection pressure (90 MPa) the results show that the first luminous emissions from the ignition zone occur very close to the injector exit followed by rapid luminous flame spreading.

An emissions and performance study was performed to show the effects of injection pressure, nozzle hole inlet condition (sharp and rounded edge) and nozzle included spray angle on particulate, NOx, and BSFC. The tests were conducted on a fully instrumented single-cylinder version of the Caterpillar 3406 heavy duty engine at 75% and 25% load at 1600 RPM. The fuel system consisted of an electronically controlled, hydraulically actuated, unit injector capable of injection pressures up to 160 MPa. Particulate versus NOx trade-off curves were generated for each case by varying the injection timing. The 75% load results showed the expected decrease in particulate and flattening of the trade-off curve with increased injection pressure. However, in going from 90 to 160 MPa, the timing had to be retarded to maintain the same NOx level, and this resulted in a 1 to 2% increase in BSFC. The rounded edged nozzles were found to have an increased discharge coefficient.

A multi-dimensional model was used to calculate interactions between spray drops and gas motions close to the nozzle in dense high-pressure sprays. The model also accounts for the phenomena of drop breakup, drop collision and coalescence, and the effect of drops, on the gas turbulence. The calculations used a new method to describe atomization (a boundary condition in current spray codes). The method assumes that atomization and drop breakup are indistinguishable processes within the dense spray near the nozzle exit. Accordingly, atomization is prescribed by injecting drops (‘blobs’) that have a size equal to the nozzle exit diameter. The injected ‘blobs’ breakup due to interaction with the gas as they penetrate, yielding a core region which contains relatively large drops. The computed core length agrees well with available measurements of core length in high-pressure sprays.

In the Atomization regime, liquid jets breakup either within the nozzle or immediately upon entering the chamber gas and drops much smaller than the jet diameter are formed. The mechanism of Atomization, which is presently unknown, was investigated by the simultaneous use of two photographic techniques. The initial transient was observed with a 106 frames/s camera and the steady state by a technique similar to spark photography. The experiment range was: liquid pressure 500 to 2500 psia; five mixtures of water and glycerol to vary the liquid viscosity; air, nitrogen, helium, and xenon at up to 600 psia as chamber gases to separate gas pressure from gas density effects; and 14 nozzle designs. Not changed were the temperature (room value), the nozzle diameter (340 μ), and the surface tension (70 dyne/cm).