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Technical Paper

The Influence of Bowl Offset on Air motion in a Direct Injection Diesel Engine

The influence of bowl offset on motored mean flow and turbulence in a direct injection diesel engine has been examined with the aid of a multi-dimensional flow code. Results are presented for three piston geometries. The bowl geometry of each piston was the same, while the offset between the bowl and the cylinder axis was varied from 0.0 to 9.6% of the bore. The swirl ratio at intake valve closing was also varied from 2.60 to 4.27. It was found that the angular momentum of the air at TDC was decreased by less than 8% when the bowl was offset. Nevertheless, the mean (squish and swirl) flows were strongly affected by the offset. In addition, the distribution of turbulent kinetic energy (predicted by the k-e model) was modified. Moderate increases (10% or less) in mass averaged turbulence intensity at TDC with offset were observed. However, the TDC turbulent diffusivity was changed less than 3% due to a slight decrease in turbulent length scale with increasing offset.
Technical Paper

The Effects of Emulsified Fuels and Water Induction on Diesel Combustion

Water was inducted with the intake air and injected emulsified with the fuel, in a conventional single cylinder D.I. diesel engine. The major effects of inducted water were an increase in ignition delay, and reduction in the oxides of nitrogen and smoke at a constant fuel/air ratio. When the water was emulsified with the fuel, the ignition delay increased so much that no benefits were obtained except for a reduction in smoke. The results are compared to a similar study on an engine with the “M” combustion system. The major differences between the results obtained with the two combustion systems are attributed to the differences in the ignition delay caused by the water addition.
Technical Paper

New Piston Telemetry Applied to Spherical Joint Piston Development

A new telemetry system has been developed for temperature or strain measurements on a spherical joint piston. The system includes a piston mounted signal multiplexer and transmitter. A patented, piston mounted power generator operates in conjunction witii a modified cylinder liner. The telemetry system is robust, having high inertia load capability and high environmental temperature operating capability. The telemetry system was installed and operated on an engine motoring test rig. Temperature signals were transmitted at engine speeds from 400 rpm to 2100 rpm. Over 100 hours of high engine speed testing with oil sump temperatures up to 122°C were completed.
Technical Paper

Experimental and Analytical Studies of Cylinder Head Cooling

Previous work on the cooling jackets of the Cummins L10 engine revealed flow separation, and low coolant velocities in several critical regions of the cylinder head. The current study involved the use of detailed cooling jacket temperature measurements, and finite element heat transfer analysis to attempt the identification of regions of pure convection, nucleate boiling, and film boiling. Although difficult to detect with certainty, both the measurements and analysis pointed strongly to the presence of nucleate boiling in several regions. Little or no evidence of film boiling was seen, even under very high operating loads. It was thus concluded that the regions of seemingly inadequate coolant flow remained quite effective in controlling cylinder head temperatures. The Cummins L10 upon which this study has focused is an in-line six cylinder, four-stroke direct injection diesel engine, with a displacement of 10 liters.
Technical Paper

Comparison of Measured and Theoretical Inter-Ring Gas Pressure on a Diesel Engine

Inter-ring gas pressure and piston ring motion are considered important for the control of oil consumption, particulate emissions, and reduced friction. For this reason, inter-ring gas pressure was measured on a diesel engine. Two different ring pack configurations were tested (positive and negative twist second rings). A significant difference in measured inter-ring pressure was observed. The measurements were compared to the predictions of a cylinder kit model with favorable results. Predictions showed that the observed difference between measured inter-ring pressures is caused by a significant difference in ring motion. The reasons for these differences are explained in this paper.
Technical Paper

Combustion Chamber Component Analysis for Advanced Heavy Duty Diesel Engines

Detailed thermal analysis was conducted on several advanced cylinder head, liner, and piston concepts, for low heat rejection diesel engines. The analysis was used to define an optimized engine configuration. Results pointed to the strategic use of oil cooling and insulation in the cylinder head, an oil cooled cylinder liner, and an insulated piston, with separate insulation behind the compression rings. Such a configuration reduced in-cylinder heat rejection by 30 percent, while durability would be expected to be maintained or improved from today's production levels.
Technical Paper

An Evaluation of the Lucas Combustion Noise Meter on Cummins ‘B’ Series Engines

Lucas Industries Noise Centre has introduced a combustion noise meter which is designed to predict the contribution of the combustion process to overall diesel engine noise. The performance of the meter is evaluated using Cummins B series engines in naturally-aspirated and turbocharged form. Combustion noise levels predicted by the meter are compared to levels determined using traditional techniques. The effects of several engine operating parameters on combustion noise are investigated under both steady state and accelerating conditions. The meter reliably predicts changes in combustion noise levels, and is a useful tool for performance development engineers. Combustion noise is shown to be related to the maximum rate of pressure rise at the onset of combustion, but combustion noise is not reliably related to maximum cylinder pressures.
Technical Paper

A Transient Spray Mixing Model for Diesel Combustion

A transient spray mixing model forming the basis of heterogeneous combustion in direct injection diesel engines is described. Experimental results of transient fuel sprays in a high pressure, high temperature chamber form the basis of spray growth equations. Use of similarity of concentration profile across the spray in conjunction with spray geometry and mass conservation yields a complete description of spatial and temporal fuel-air distribution. Fuel preparation and air entrainment rates are calculated from the history of fuel-air distribution. Progressive evolution of combustion zones is determined by the fuel-air mixing process. Energy conservation and chemical kinetics calculations in each zone yield cylinder pressure and local nitric oxide concentration. The role of fuel-air mixing in diesel combustion is discussed. The model results are compared with experimental data.