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The outflow of the products of combustion from a two-stroke cycle diesel engine cylinder is examined and the numerical analysis used hitherto supplanted by a direct integration method. It is found that the equations of outflow result in a nonlinear differential equation capable of direct solution, thereby giving rapid computation of the exhaust lead, one of the most important single criteria of the overall engine design.

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.

This paper describes a unique design of deflector piston for a cross-scavenged two-stroke cycle engine which incorporates the advantages of good scavenging, rapid combustion and reduced thermal loading on the piston. Test results are presented to confirm this statement from two small capacity outboard marine engines and comparisons are made between the experimental test results from the modified and standard power units; of significance is the reduced fuel consumption rate of the modified engines in both cases. A high bmep 400 cm3 single cylinder engine is designed, constructed and tested so as to determine the extent of deflector burning under conditions of high thermal loading. On all three engines the ignition timing for best power is shown to be in the 21-24° btdc region, by comparison with 32-38° btdc conventionally. The spark plug seat temperatures are reduced to 150 C maximum at peak power by comparison with 250-280 °C normally.

In a previous paper (6)* SAE 850178, the authors pointed out that the single-cycle gas simulation rig which they had developed would prove to be an invaluable experimental tool for the development of two-stroke cycle engine cylinders to attain better scavenging and trapping efficiency of the fresh charge. This paper reports on the use of that now proven experimental technique to examine one of the longest running, and hitherto unresolved, discussions in the field of small two-stroke cycle engines: is loop-scavenging really superior to cross-scavenging? All of the cross-scavenging tests in the paper are compared to tests conducted on loop-scavenged cylinders of the same basic geometry and which were reported previously to SAE. The main conclusion from the experimental investigation is that cross-scavenging is superior to loop-scavenging at low or modest scavenge ratios but is inferior at high scavenge ratios.

Previous publications from The Queen's University of Belfast have shown the formulation of a mathematical model to simulate the dynamic behaviour of a reed valve as used between the crankcase and inlet tract of a simple two-stroke cycle engine. This paper describes the enhancements and improvements made to this original reed valve model and its verification by correlation with measurements from a firing engine. Measured and predicted data for reed tip lift and delivery ratio are presented for a 350cm3, twin cylinder test engine over a wide range of engine speeds up to 9500 rev/min. The results of this experimental and theoretical study, using varied reed width profiles and radically different reed petal materials including carbon fibre, glass fibre reinforced plastics and steel, are also presented. The development of a new and unique reed valve visualisation technique is described and discussed both theoretically and practically.

Wave effects in exhaust systems can strongly influence the performance of an engine. Predictions of pressure-time variations at the exhaust valve by graphical methods, based on experience and the assumption that exhaust pulses will act as sound waves, have been of no design value with multicylinder engines. Now a numerical method, developed from the graphical has been programmed for a computer making possible rapid calculation on nonsteady flow properties of an exhaust system. When augmented by experimental testing of three disparate exhaust systems, such calculation proved useful in the design of exhaust systems for multicylinder automobile engines. This Paper describes the engine investigations of the three systems involved and the derived design conclusions.

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.

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.

A combined one-dimensional, multi-dimensional computational fluid dynamic modelling technique has been developed for analysis of unsteady gas dynamic flow through automotive mufflers. The technique facilitates assessment of complex designs in terms of back-pressure and noise attenuation. The methodology has been validated on a number of common exhaust muffler arrangements over a wide range of test conditions. Comparison between measured and simulated data has been conducted on a Single-Pulse (SP) rig for detailed unsteady gas dynamic analysis and a Rotary-Valve (RV) rig in conjunction with an anechoic chamber for noise attenuation analysis. Results obtained on both experimental arrangements exhibit excellent gas dynamic and acoustic correlation. The technique should allow optimisation of a wide variety of potential muffler designs prior to prototype manufacture.

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 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.

This paper reports on the use of mathematical modelling by the GPB method of pressure wave propagation through finite systems, for the design of prototype exhaust systems and silencers for a Harley-Davidson motorcycle. The motorcycle engine is the classic 1340 cm3 45° V-twin power unit. The design objectives were to gain mid-range power and torque without loss of performance at either end of the speed range and to design silencers which would enhance the performance and the noise image of the machine. The Queen's University of Belfast (QUB) (3)* employed their unsteady gas flow modelling techniques to the design of the system and its silencers to complement a new camshaft design from Crane Cams. The results of the use of these computer based design techniques are reported as performance characteristics of power and torque for the new design by comparison with the stock system.

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 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.

A study of fuel injection during the open cycle of a small spark ignition two-stroke cycle engine has been carried out. A manually controlled electronic fuel injection system has been used as this appears to have many advantages over mechanically controlled equipment. Various injection locations were considered and injection timing and air/fuel ratio varied at each position to determine optimum power and bsfc requirements. The results presented are compared with baseline carburation and with fuel injection into the intake to assess the potential improvements gained from each injector location.

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.

An earlier paper by Blair and Cahoon (SAE 710082) described the initial design and development of a 60 hp engine of the single-cylinder 2-cycle type for road racing motorcycle applications. This paper continues with the further design of this engine as a 65 hp 5-speed transmission unit and a variation of it as a 40 hp 4-speed transmission engine for moto-cross racing usage. A discussion of the application of the computer to the design of both engines is included. The computer design is used for the prediction of the required torque/speed characteristics for both engines for their particular application in order to eliminate lengthy test bed development. The mechanical design criteria for the engine/transmission units are also discussed and their implementation for the road race or moto-cross application described.

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.

This paper describes a unique and uncomplicated method of stratified-charging a two-stroke cycle engine which assists in reducing the short-circuited loss of fuel during scavenging. Performance characteristics as presented were acquired from tests conducted on a 400 cm3 naturally aspirated, single cylinder, spark ignition two-stroke engine with carburettor control of gasoline fuel, the design and construction of the engine also being done at The Queen's University of Belfast. Using a tuned exhaust pipe, the engine produces a peak power of 16 kW at 5000 rev/min and has a minimum brake specific fuel consumption of 0.275 kg/kWh. Moreover, for the tests presented at full and quarter throttle openings, virtually all of the brake specific fuel consumption values are below 0.36 kg/kWh. Most of the performance characteristics shown at various engine speeds are as a function of air/fuel ratio. This paper is a continuation of that presented as SAE 830093.