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The application of in-cylinder multi-dimensional modelling to the scavenging process within the cylinder of a two-stroke cycle engine requires a prior knowledge of the flow entering that cylinder. Without this information, assumptions must be made which limit the accuracy of the theoretical simulation. This paper describes laser doppler anemometry measurements of transfer port efflux flow for a two-port loop scavenged test cylinder motored at 200 rev/min. The cylinder was externally blown to ensure scavenge flow into the cylinder over the entire transfer port open period. The test results indicate that the flow does not enter the cylinder in the port design direction, but varies as a function of port height during both port opening and closing. Comparison of motoring results with those obtained under steady flow testing of the same cylinder, shows adequate correlation, thereby justifying the use of steady flow information for dynamic simulation.

An experimental and theoretical investigation to minimise the hydrocarbon emissions from a 25 cm3 two-stroke engine with finger transfer ports is described. Finger ports have the side of each passage closest to the cylinder axis open to the cylinder bore making it possible to produce high-pressure die castings with the simplest of dies. Cylinders utilising this type of porting are believed to have inferior scavenging characteristics compared to those using closed or cup-handle porting. The effects of cylinder scavenging characteristics and port optimisation on engine performance were examined using a computer simulation. It is concluded that there is potential for a 70% reduction in exhaust hydrocarbon emissions through scavenging efficiency improvements and port optimisation, provided the cylinder scavenging can be developed to match that of the best existing unconventional crossflow scavenged designs.

The paper discusses the application of maps of measured discharge coefficients for poppet valves, cylinder ports, and in-pipe throttles within a theoretical simulation of the unsteady gas flow through an internal combustion engine. The maps provided cover both inflow and outflow at the discontinuity being discussed and are displayed as contour maps of the discharge coefficient as some function of the geometrical flow area of that discontinuity and of the pressure ratio across it up to a maximum value of 2.0. An engine simulation package is used for both a four-stroke and a two-stroke engine to determine the typical pressure ratio and area ratio characteristics which pertain at all such discontinuities at representative engine speed and load conditions.

Recent environmental legislation to reduce emissions and improve efficiency means that there is a real need for improved thermodynamic performance models for the simulation of direct-injection, turbocharged diesel engines, which are becoming increasingly popular in the automotive sector. An accurate engine performance simulation software package (VIRTUAL 4-STROKE) is employed to model a benchmark automotive 1.9-litre Turbocharged Direct Injection (TDI) diesel engine. The accuracy of this model is scrutinised against actual test results from the engine. This validation includes comparisons of engine performance characteristics and also instantaneous gas dynamic and thermodynamic behaviour in the engine cylinders, turbocharger and ducting. It is seen that there is excellent agreement in all of these areas.

Engine cycle simulation is an essential tool in the development of modern internal combustion engines. As engines evolve to meet tougher environmental and consumer demands, so must the analysis tools that the engineer employs. This paper reviews the application of such a tool, VIRTUAL 4-STROKE [1], in the modelling of a benchmark 1.9 Litre TDI engine. In an earlier paper presented to the Society [2] the authors presented results of a validation study on the same engine under full load operation. This paper expands on that work with validation of the simulation model against measured data over a full range of part load operation.

A 500 cc single cylinder two-stroke engine employing cross scavenging and direct air-assisted gasoline injection is described. Preliminary engine test results are presented for 3000 rpm full load and 1600 rpm part load operating conditions. The effects of fuel injection timing on full and part load brake specific fuel consumption and exhaust emissions are examined.

The emissions produced from a simple carburetted crankcase scavenged two-stroke cycle engine primarily arise due to losses of fresh charge from the exhaust port during the scavenging process. These losses lead to inferior fuel consumption and a negative impact on the environment. Pressure on exhaust emissions and fuel consumption has reduced the number of applications of the two-stroke cycle engine over the years, however the attributes of simplicity, high power density and potential low manufacturing costs have ensured its continuing use for mopeds and motorcycles, small outboard engines and small utility engines. Even these last bastions of the simple two-stroke engine are being challenged by the four stroke alternative as emissions legislation becomes tighter and is newly formulated for many categories of engines. A simple solution is described which reduces short circuit and scavenge losses in a cost effective way.

In two previous papers to this Society (1, 2)* an ‘alternative’ method was presented for the prediction of the unsteady gas flow behaviour through a reciprocating internal combustion engine. The computational procedures led further to the prediction of the overall performance characteristics of the power unit, be it operating on a two- or a four-stroke cycle. Correlation with measurements was given to illustrate its effectiveness and accuracy. In the ducts of such engines there are inevitably sectional changes of area which are either gradual or sudden. A tapered pipe is typical of a gradual area change whereas a throttle or a turbocharger nozzle represents a sudden area change. In those previous papers it was indicated that a fuller explanation, of the theoretical procedures required to predict accurately the unsteady gas flow in such duct sections would be given in a later paper to this Society; this is that necessary publication.

This paper presents confirmation of the accuracy of prediction of an engine simulation model. The experimental data used to compare with the output of the simulation model are from a single cylinder four-stroke cycle engine and from a single-cylinder two-stroke cycle engine; both engines are naturally aspirated and use spark- ignition. In addition, for the two-stroke cycle engine, the experimental data includes two cylinders with different scavenging characteristics which induce variations of performance characteristics of up to 20%. The fundamentals of the theoretical approach have been presented before to SAE (1)* and this paper extends that theory by providing a detailed discussion on the inclusion of measured scavenging characteristics to enable the simulation model to predict the mechanism of the in-cylinder gas exchange process.

This paper reports on the first phase of an experimental evaluation of five different methods for the mathematical modelling of unsteady gas flow in engine ducting. The five methods under investigation are the homentropic method of characteristics, the non-homentropic method of characteristics, the two-step Lax-Wendroff method with flux corrected transport, the Harten-Lax-Leer upstream difference method and the Blair method of pressure wave propagation through finite spaces. A single cycle pressure wave generator consisting of a cylinder, connected via a sliding valve to a long duct, has been designed and built. The pressure waves it creates closely mimic those to be found in i.e. engines. The cylinder and the ducts of the device can be filled with any gas and at elevated temperatures. A perfect seal exists between the cylinder and the valve thus enabling mass- flow correlation. The initial cylinder pressure may be set to simulate an induction or an exhaust process.

This paper reports on the experimental evaluation of certain aspects concerning the mathematical modelling of pressure wave propagation in engine ducting. A particular aspect is the coefficient of discharge of the various ports, valves or apertures of the ducting connected to the cylinder of an engine or to the atmosphere. The traditional method for the deduction of the coefficients of discharge employs steady flow experimentation. While the traditional experimental method may well be totally adequate, it is postulated in this paper that the traditional theoretical approach to the deduction of the discharge coefficient from the measured data leads to serious inaccuracies if incorporated within an engine simulation by computer. An accurate theoretical method for the calculation of the discharge coefficient from measured data is proposed.

This paper reports on the first phase of an experimental evaluation of four different methods for the mathematical modelling of unsteady gas flow in a pipe system containing an area discontinuity. The four methods under investigation are the non-homentropic method of characteristics, the two-step Lax-Wendroff method with flux corrected transport, the Harten-Lax-Leer upstream difference method and the GPB finite system method. The experimentation is conducted using the QUB SP (single-pulse) pressure wave generator consisting of a cylinder, connected via a sliding valve to a long duct. The pressure waves it creates closely mimic those to be found in i.c. engines. The initial cylinder pressure may be set to simulate either an induction or an exhaust process. Various ducts are attached to the pressure wave generator to simulate both sudden and gradual area changes. Each duct is sufficiently long as to permit pressure wave observation without superposition effects.

This paper reports on the experimental evaluation of certain aspects of the mathematical modelling by the GPB method of pressure wave propagation through finite systems, of unsteady gas flow in engine ducting. The aspects under examination are the propagation of pressure waves through a pipe which contains gases of dissimilar properties. In this case the gases are carbon dioxide and air. The experimentation is conducted using the QUB SP (single pulse) pressure wave generator consisting of a cylinder, connected via a sliding valve to a long duct. The pressure waves it creates closely mimic those to be found in i.e. engines. The initial cylinder pressure may be set to simulate either an induction or an exhaust process, but the experiments reported here are of compression waves only. The duct attached to the pressure wave generator is a straight pipe. The cylinder and part of the pipe are filled with carbon dioxide and air.

This paper describes the initial investigation and design of a lightweight racing motorcycle with a single-cylinder 2-stroke engine, capable of producing 60 bhp. The data discussed here pertain to the gas dynamic and mechanical parts and functions of the cycle. Designs of the various components are described and reports of tests on road and test beds verify the viability of this concept of a high specific output and large displacement cylinder for a lightweight, air-cooled motorcycle engine.

From a theoretical analysis of the unsteady efflux from the open end of a simulated reciprocating internal combustion engine exhaust system a prediction of overall and one-third octave sound pressure levels in space, due to this gas flow, is produced. The predictions are compared with measured levels and show a high degree of correlation.

The performance characteristics of a naturally aspirated two-cycle engine can be predicted with an unsteady gas dynamics analysis of flow through the crankcase and cylinder; such an analysis provides values of volumetric efficiency and trapping pressure at any given engine speed. The predictions of the volumetric efficiency and trapping pressure are compared with experimental values from a high-specific-output engine and further amplified with theoretical/experimental comparisons of pressure-time histories taken in the exhaust, transfer, and inlet systems at several engine speeds. The theoretical derivation of unsteady gas dynamic cylinder to pipe boundary conditions is presented so that they become both economical of computer time and mathematically stable.

A computer program has been developed which predicts the sound pressure level and the frequency spectrum produced by simple engine exhaust systems. The program utilizes unsteady flow gas dynamic theory to predict the pressure-time history in the exhaust system and the velocity-time history at the open end of the system. Acoustic theory is then used to predict the sound pressure levels and frequency spectrum in free space. The work was carried out on a twin-cylinder four-cycle engine, but the theory can be applied to any internal combustion engine.

The study of scavenge flow in two-cycle engines is of great importance in the development of that type of internal combustion engine and has been extensively covered by numerous researchers over the last half -century. Alfred Jante in SAE paper 680468 suggested an indirect and comparative test for the assessment of scavenge flow which he, and others, have shown to be both a simple and extremely relevant technique. The acquisition and reduction of data for this experimental method proved to be laborious and time consuming, and it is the purpose of this paper to show that it is possible to eliminate these tedious aspects by automation of both data recording and processing. This is described and examples of its usage are given.

This paper describes a theoretical and experimental investigation of the noise characteristics of some basic internal combustion engine exhaust systems. On the basis of a one-dimensional analysis of the unsteady internal flow, the treatment is extended to consider the noise radiated by the efflux of gas from the atmospheric termination of the tail pipe. Using a rotary valve exhaust simulator, experimental pressure-time histories and one-third octave noise spectrograms were obtained. These are compared with those calculated.

In 1968 Professor Alfred Jante published an SAE paper detailing a method of assessing the scavenging behaviour of a two-cycle engine. It was a simple technique involving motoring the engine and measuring the (cylinder head removed) velocity contours at the cylinder head level using pitot tubes. It attracted wide attention in industry, but with varying degrees of acceptance and results. This paper attempts to establish in a logical manner and with a considerable’ volume of experimental data that the method proposed by Jante has real relevance, but to obtain acceptable accuracy in terms of predicting good and bad scavenging for particular engine cylinders the results have to be analysed rather more carefully and completely than the approach adopted by Jante.