Typical Engine Conditions Research Articles

Spray/wall interaction influences on the diesel engine mixture formation process investigated by spontaneous Raman scattering

A main topic for the further development of direct injection diesel engines is the optimization of mixture formation, as all subsequent processes like ignition, combustion, and pollutant formation are mainly influenced by the local air/fuel ratio inside the cylinder. Especially for passenger-car engines, the interaction between spray and combustion chamber walls is an important issue for mixture formation. Therefore, this interaction was the subject of the investigations described. The investigations were carried out in a heatable high-pressure high-temperature chamber under typical diesel engine conditions of 450°C temperature and 50 bar pres'sure. A passenger-car common rail system was used as injection system which could be equipped with two different six-hole nozzles, both with common rail specific seat geometry, mini sac hole geometry, and double needle guide. In order to allow a detailed evaluation of the quality of mixture formation, a measurement technique based on spontaneous Raman scattering was applied, enabling quatitative measurements of the local air/fuel ratio along a line of a few milimeters. The careful adaptation of the optical setup made it possible to separate the weak Raman signals from background contributions, and this allowed a distinct determination of air and fuel density in the vapor phase. The measurements were carried out at a distance of 2 mm from the wall, directly above the impact location of the spray jet, as well as inside the wall jet region. The results obtained indicate the improvement of the mixture formation inside the wall jet as-consequence of the increased air entrainment. Additionally, for the investigation of the temporal development of mixture formation, the influences of injection pressure, nozzle orifice geometry, and wall surface temperature on mixture formation have been studied.

Numerical Analysis of Heat Pipe Turbine Vane Cooling

A numerical model was developed to simulate transient performance of a heat pipe turbine vane under typical gas turbine engine conditions. Curvilinear coordinates were used to describe the three-dimensional wall and wick heat conduction coupled with the quasi-one-dimensional vapor flow. A unique numerical procedure including two iterative “estimate-correction” processes was proposed to efficiently solve the governing equations along with the boundary conditions. Comparisons with experimental results validated the numerical model and the solution method. A detailed numerical simulation of the heat pipe vane’s transient performance indicated the benefits of incorporating heat pipe vane cooling as well as the areas where precautions should be taken while designing heat pipe vanes.

Effects of Surface Roughness on Heat Transfer and Aerodynamic Performance of Turbine Airfoils

Aerodynamic flow path losses and turbine airfoil gas side heat transfer are strongly affected by the gas side surface finish. For high aero efficiencies and reduced cooling requirements, airfoil designs dictate extensive surface finishing processes to produce smooth surfaces and enhance engine performance. The achievement of these requirements incurs additional manufacturing finishing costs over less strict requirements. The present work quantifies the heat transfer (and aero) performance differences of three cast airfoils with varying degrees of surface finish treatment. An airfoil, that was grit blast and Codep coated, produced an average roughness of 2.33 μm, one that was grit blast, tumbled, and aluminide coated produced 1.03 μm roughness, and another that received further postcoating polishing produced 0.81 μm roughness. Local heat transfer coefficients were experimentally measured with a transient technique in a linear cascade with a wide range of flow Reynolds numbers covering typical engine conditions. The measured heat transfer coefficients were used with a rough surface Reynolds analogy to determine the local skin friction coefficients, from which the drag forces and aero efficiencies were calculated. Results show that tumbling and polishing reduce the average roughness and improve performance. The largest differences are observed from the tumbling process, with smaller improvements realized from polishing.

An Experimental Study of Turbine Vane Heat Transfer With Water–Air Cooling

This paper presents data showing the improvement in cooling effectiveness of turbine vanes through the application of water–air cooling technology in an industrial/utility engine application. The technique utilizes a finely dispersed water-in-air mixture that impinges on the internal surfaces of turbine airfoils to produce very high cooling rates. An airfoil was designed to contain a standard impingement tube, which distributes the water–air mixture over the inner surface of the airfoil. The water flash vaporizes off the airfoil inner wall. The resulting mixture of air–steam–water droplets is then routed through a pin fin array in the trailing edge region of the airfoil where additional water is vaporized. The mixture then exits the airfoil into the gas path through trailing edge slots. Experimental measurements were made in a three-vane, linear, two-dimensional cascade. The principal independent parameters—Mach number, Reynolds number, wall-to-gas temperature ratio, and coolant-to-gas mass flow ratio—were maintained over ranges consistent with typical engine conditions. Five impingement tubes were utilized to study geometry scaling, impingement tube-to-airfoil wall gap spacing, impingement tube hole diameter, and impingement tube hole patterns. The test matrix was structured to provide an assessment of the independent influence of parameters of interest, namely, exit Mach number, exit Reynolds number, gas-to-coolant temperature ratio, water-and air-coolant-to-gas mass flow ratios, and impingement tube geometry. Heat transfer effectiveness data obtained in this program demonstrated that overall cooling levels typical for air-cooled Vanes could be achieved with the water–air cooling technique with reductions of cooling air flow of significantly more than 50 percent.

Analysis of Bearing Incidents in Aircraft Gas Turbine Mainshaft Bearings

An examination of approximately 200 bearing incidents in current aircraft engines has shown that damage in the bearing is initiated at the surface. Twenty-one cases were studied in detail, and five typical incidents are presented here. The initial damage was produced by abrasive particles, dents, grinding scores, skidding, large carbides and corrosion pits. The first phase of the failure mechanism appeared to be by peeling, where microscopic regions about 0.13 mm (0.005 in) were removed from the surface, and the peels eventually developed into spalls. These mechanisms of failure are a consequence of the partial EHD lubrication utilized in these bearings, and the consequent sharing of the load by the asperities and the EHD film. Failures of this type were reproduced in lest bearings run under typical engine conditions, and these tests were used to study the peeling mechanism. Techniques for the minimization of surface-initiated fatigue are also discussed. Presented at the 45th Annual Meeting In Denver, Col...

Acoustic properties of heated twin jets

A thorough experimental study of the noise characteristics of twin jets is presented in this paper. Twin round jets are investigated at typical jet engine conditions: that is, with heated high velocity flow. By varying the nozzle to nozzle spacing, it is possible to discriminate between the effects of turbulent mixing and acoustic shielding. As a result of this investigation, it was established that the turbulent mixing effects (both interaction noise generation and mixing suppression) occur for closely spaced nozzles. While acoustic shielding occurs at all nozzle spacings, it plays the dominant role at wide nozzle spacings. The levels of this acoustic shielding afforded by an adjacent jet can be sufficient to cause a nearly complete masking of the noise of the shielded jet. A significant discovery of this investigation was the importance of the layer of cooler, slower moving ambient air that exists between the twin jet plumes. This inter-jet layer causes acoustic refraction and reflection, and as the nozzle separation increases, the layer extends to shield more of the jet noise sources.

Condensation and Laser Attenuation in Water Plumes from a Laser-Propelled Rocket

This paper investigates condensation and absorption of CO 2 laser radiation in water-vapor plumes at various altitudes with specific application to laser propulsion of rockets. At high altitudes (>90 km) the plume was modeled as an expansion into vacuum; the expansion leads to cooling and condensation. Absorption both by condensed water droplets and by water vapor was found to be negligible ( —5 x 10 ~3). At intermediate and low altitudes (<20 km) the plume cools by entraining ambient air. We find that for typical engine conditions condensation is unlikely if the ambient air is dry. Absorption by water vapor was found to be negligible at 20 km (<10 ~ 3) and small at sea level (-4%). However, limited broadband water-vapor absorption data indicate that the actual absorption could be up to a hundred times greater due to high-temperat ure absorption lines not included in the present calculations. High-resolution transmissivity measurements at the exact location of the CO2 lines are needed for definite conclusions to be drawn near sea level.