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Technical Paper

A Multi-Pipe Junction Model for One-Dimensional Gas-Dynamic Simulations

Computer programs that simulate the wave propagation phenomena involved in manifold tuning mechanisms are used extensively in the design and development of internal combustion engines. Most comprehensive engine simulation programs are based on the governing equations of one-dimensional gas flow as these provide a reasonable compromise between modelling accuracy and computational speed. The propagation of pressure waves through pipe junctions is, however, an intrinsically multi-dimensional phenomenon. The modelling of such junctions within a one-dimensional simulation represents a major challenge, since the geometry of the junction cannot be fully represented but can have a major influence on the flow. This paper introduces a new pressure-loss junction model which can mimic the directionality imposed by the angular relationship of the pipes forming a multi-pipe junction. A simple technique for estimating the pressure-loss data required by the model is also presented.
Technical Paper

Studying the Effectiveness of Multi-Stage Fuel Injection in a Dl Diesel Engine using Combustion Visualisation and the Spectroscopic Method

IC Engines are widely used as power plants for automobiles. The rapid growth in the number of automobiles has caused increased environmental pollution. Therefore, emission legislation was introduced to keep the pollution within acceptable limits. It is becoming more stringent day by day, and is the driving force for the development and application of various experimental and computational techniques for engine combustion and emission studies. Multi-stage fuel injection, VCO nozzles, retarded fuel injection timing, reentrant combustion chamber, etc. are some of the means of reducing the exhaust emissions. A study involving in-cylinder combustion visualisation and an optical method (spectroscopic method) is reported in this paper. Using this technique, the effect of multi-stage fuel injection at various engine operating conditions was studied. A Ricardo Hydra single cylinder, direct injection optical diesel engine was used for this study.
Technical Paper

Steady-Flow Loss-Coefficient Estimation for Exhaust Manifold Pulse-Converter Type Junctions

Computer programs to simulate the gas dynamics of internal combustion engines are commonly used by manufacturers to aid optimization. These programs are typically one-dimensional and complex flow features are included as ‘special’ boundaries. One such boundary is the ‘pressure-loss’ junction model, which allows the inclusion of directionality effects brought about by the geometry of a manifold junction. The pressure-loss junction model requires empirical, steady-flow pressure-loss data, which is both time consuming and expensive to obtain, and also requires the junction to be manufactured before its performance can be established. This paper presents a technique for estimating the steady-flow data, thus obviating the need to perform these flow-tests.
Technical Paper

Multi-Dimensional Wave Propagation in Pipe Junctions

The propagation of pressure waves through junctions in engine manifolds is an intrinsically multi-dimensional phenomenon. In the present work an inviscid two-dimensional model has been applied to the simulation of shock-wave propagation through 45° and 90° junctions: the results are compared with schlieren images and measured pressure-time histories. The HLLC integral state Riemann solver is used in a shock-capturing finite volume scheme, with second-order accuracy achieved via slope limiters. The model can successfully predict the evolution of the wave fronts through the junctions and the high frequency pressure oscillations induced by the transverse reflections. The calculation time is such as to make it feasible for inclusion, as a local multi-dimensional region, within a one-dimensional wave-action engine simulation.
Technical Paper

Evaluation of the Intensity of Turbulent Velocities by Using a Cross-Correlation Technique for Pattern Tracking

This paper reports the development of a method for evaluating the intensity of turbulent velocities by using a cross-correlation technique for pattern tracking. With this method, only a pair of flow field images having a short time interval between them is required to perform the evaluation. The method is verified partially by its ability, when it is simplified, to reveal several phenomena observed previously in the velocity measurement by the cross-correlation technique for pattern tracking. An application to the estimation of turbulent intensity in a diesel engine combustion chamber after combustion is described.
Technical Paper

3D Modelling and Photographic Investigation of Combustion in Hydra DI Diesel Engine

High speed photographs of spray and combustion, obtained from a Hydra direct injection research diesel engine are compared with the predictions made by KIVA-3 computer code. The preprocessor has been modified to generate a grid for an offset bowl and the postprocessor has been extensively reprogrammed to obtain contour maps. The model has been tuned to low load at 2000rpm. Then the predictive capability of the model has been verified at other operating conditions. Predicted results show very good agreement with the experimental data.
Technical Paper

A Study of Warm-Up Processes in SI Engine Exhaust Systems

The improvement of exhaust emission during engine warm-ups is vital in engine emission control as engine emission limits are constantly lowered. An effective solution to this problem is to install a rapid-warming catalyst. On the other hand, precaution also has to be taken to avoid overheating of the catalyst. These require detailed information on heat transfer and accurate gas temperature variations at different locations in the exhaust system. In this study, experiment was conducted to investigate how mean gas and pipe wall temperatures vary during warm-ups throughout the exhaust systems, as well as the time constants of the transient processes. In addition, a program was developed for the simulation of exhaust gas and pipe wall temperatures during warm-ups. The temperatures were time-averaged in every engine cycle but variable from cycle to cycle.
Technical Paper

Influence of Swirl on High Pressure Injection in Hydra Diesel Engine

The influence of swirl on performance and emissions was investigated using a single cylinder Hydra research engine fitted with a high pressure electronic unit injector and a variable swirl mechanism. A large amount of emission data was collected together with the cylinder pressure, fuel line pressure and needle lift signals at a wide range of operating conditions. The influence of a fixed swirl ratio on emissions was also investigated on a Ford HSD425 York engine with conventional injection system and a synopsis of the results is discussed. Laser illuminated high speed cinematography was used to study the interaction of swirl with spray and combustion processes. Data is presented on air- fuel mixing, spray trajectories and flame movement at different operating conditions. Data is also presented to highlight the influence of swirl on the heat release rate, cylinder pressure rise and its relation to measured emission levels, particularly NOx and particulates.
Technical Paper

Laser Illuminated Photographic Studies of the Spray and Combustion Phenomena in a Small High Speed DI Diesel Engine

A large number of high speed photographs have been taken of combustion in a high speed direct injection diesel engine. A frame rate of upto 20,000 frames/sec has been achieved at engine speeds up to 3000 rev/min. This has been achieved by computer controlled synchronization of a Cu-vapour laser illumination source, the high speed camera and the electronically controlled fuel injection equipment. In addition to the photography, the basic macroscopic parameters of combustion were recorded simultaneously: this enables the photographic information to be related to the heat release information. The parameters investigated include the influence of swirl ratio, injection system, engine speed, load, injection timing, and combustion chamber shape on spray and combustion. The influence of various parameters on spray growth, ignition and combustion is discussed. Combustion processes in open and reentrant open bowl combustion chambers are examined.
Technical Paper

A Rapid Wave Action Simulation Technique for Intake Manifold Design

The volumetric efficiency of reciprocating internal combustion engines is a strong function of intake manifold configuration. A computationally efficient simulation technique is described which is based on the linearised one-dimensional conservation equations for distributed parameter systems and is amenable to the requirements of the designer in directly assessing the comparative merits of a large number of manifold configurations. Comparisons of measured and predicted volumetric efficiency curves are presented together with predicted results which illustrate the benefits to be obtained from variable geometry induction systems. The technique was found to be over 220 times faster than a comprehensive simulation program based on the method of characteristics.
Technical Paper

The Accuracy of Calculating Wave Action in Engine Intake Manifolds

This paper describes a comparison between calculated and measured pressure traces and air mass flows through a family of inlet manifold geometries. It is shown that a non-linear wave action calculation technique, based on the method of characteristics, can accurately predict the detailed variation of pressure in the manifold over a broad range of engine speed: it can also accurately predict the mass flow. It is shown that it is necessary to include end effects for the various pipes in order to obtain realistic predictions. The mass flow can be predicted to better than 2% over the majority of the engine operating speed, although the accuracy decreases slightly at the tuning speeds. This reduction in accuracy is probably due to the increased losses resulting from the higher velocities and flow reversals occurring at the tuned speeds.
Technical Paper

Flow With Variable Specific Heats in The Exhaust Pipe System Of The Internal Combustion Engine

This paper describes the numerical solution of unsteady flow in the exhaust pipe system of supercharged diesel engines. The solution takes into account the change of specific heats that can occur in the flowing gas. A combination of two well-known methods is used. The flow in the pipe system is solved by the two-step differential Lax-Wendroff method while the boundary conditions are solved by the method of characteristics. The results show that the variation of the specific heats mainly influences the temperature development just upstream of the turbine of the turbocharger. Thus, with this method it is possible to determine more precisely the total mass flow, turbine output parameters and the matching point of the turbocharger.
Technical Paper

A Comprehensive Study of Wankel Engine Performance

An extensive experimental and analytical study of the performance of a Wankel engine is reported, with special emphasis on the combustion process. A one dimensional technique for calculating gas velocities in the combustion chamber under motoring conditions is described and this is then used to evaluate flame travel when combustion occurs. A novel three-zone combustion model is introduced. The effect of the position of the rotor recess is examined and shown to change the engine power output and hydrocarbon emissions.
Technical Paper

Transportation of Liquid Fuel Droplets in the Pulsative Air Flow Within the S.I. Engine Intake Manifold

An extensive amount of research has been carried out by various authors on the entrainment of fuel droplets in a steady air flow, in order to understand the transportation of droplet fuel in the spark-ignition engine intake manifold system. However, the utility of this type of steady state model is very limited when applied to the real engine where the air flow is highly pulsative. The present work develops a theoretical model of the flow of fuel droplets entrained in a non-steady air flow which requires the solution of a set of unsteady one-dimensional two phase flow equations by a numerical technique. This model is then applied to a single-cylinder spark-ignition engine fitted with both intake and exhaust manifold systems and also a carburettor.
Technical Paper

The Variation of Friction and Combustion Rates During Diesel Engine Transients

A comprehensive investigation of the performance of a 6-cylinder turbocharged engine was undertaken under steady state and transient conditions. Friction was measured under steady state conditions and a formula for calculating fmep is proposed. It was found that friction under transient conditions is higher than would be predicted from quasi-steady considerations. A combustion model was applied to the engine during steady state and transient conditions. It was found that combustion deteriorated under transient conditions even after including turbocharger lag effects.
Technical Paper

A Dynamic Simulation of a Two-Stroke Turbocharged Diesel Engine

The use of cycle simulation computer programs for the study of both the steady and transient performance of turbocharged diesel engines has provided very useful information for their design and development. This paper describes the development of a dynamic simulation of a two-stroke turbocharged diesel engine. The mathematical model for the system has been developed using the filling and emptying concept. The simulation also includes the characteristics of the turbocharger compressor, turbine, scavenge blower and intercooler. A single zone combustion model has been used to calculate the rate of heat release in the engine cylinder from the fuel injection data. The steady state performance calculation shows a very good correlation with experimental results. Parametric studies were undertaken into the effect of friction and combustion during transient running; these show that the level of friction and the rate of combustion have a great effect on the response rate.
Technical Paper

Computer Aided Design Package for Diesel Engine Manifold System

An interactive computer program for predicting the performance of a total engine system is described. The facilities include the basic design of the valve time-area diagrams, starting from various cam profiles, wave action effects in inlet and exhaust manifolds and turbocharger matching. The program is accessed via visual display units (VDUs) and its interactive nature takes many activities from the realm of the research department into that of the design department. The results obtained from the program are validated by comparison with a well-known more sophisticated wave action program.
Technical Paper

Transient Response of Turbocharged Diesel Engines

The problem of highly rated turbocharged diesel engines operating under transient load conditions is now well known, and is due to the inability of the turbocharger to supply sufficient air for good combustion. In Part 1, two methods are discussed for reducing turbocharger lag-air injection onto the compressor rotor and oil injection onto a small pelton wheel mounted on the turbocharger shaft. Results are given showing the benefit of fitting these devices to an engine on a test bed. Engine response is improved in all respects particularly smoke and overall response time. In Part 2, a simulation study of a turbocharged diesel engine installed in a 32 tonne truck is presented to investigate the engine performance during load and speed changes. It is shown that by injecting compressed air on to the turbocharger compressor rotor tip, smoke emissions from the engine during load changes are reduced.