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The performance characteristics of naturally aspirated 4-stroke cycle engines are influenced by the through-flow or exchange of fresh charge for exhaust gas during the valve overlap period. During this gas exchange period the influence of unsteady wave effects in both inlet and exhaust systems are most important. Pressure-time histories were measured at various tract locations for four inlet/exhaust configurations to demonstrate the effects of wave action on performance. The good correlation shown between measured and predicted pressure-time histories suggested that the theoretical technique may be used in further design analyses with a high degree of confidence.

Previous publications from The Queen's University of Belfast have described the unsteady gas flow through a naturally aspirated two-cycle engine and the most recent of these have detailed the scavenge process, the combustion model and muffler design. It is thus now possible to predict the unsteady gas flow behaviour through and the performance and noise characteristics in this type of engine with a good degree of accuracy. This paper describes a mathematical model which has been formulated to simulate the action of the two-cycle engine fitted with a reed valve due to the unsteady gas dynamic behaviour in the inlet tract and makes comparisons with measurements. A complete simulation on the computer of a two-cycle engine fitted with a reed intake valve is thus now possible.

Pressure-time variations are recorded in the intake pipe and crankcase of a motored, crankcase compression, piston ported, loop scavenged two stroke cycle engine over a range of engine speeds from 2000-7000 rpm, for several intake pipe lengths and different inlet port timings. These pressure-time histories are presented together with the results of theoretical calculations, which include unsteady flow in the induction tract. Predicted delivery ratio trends are compared with measured values over the range of engine speeds and inlet tract lengths for different inlet port timings.

This paper attempts to illustrate some of the reflection characteristics of exhaust systems, suitable for piston ported, crankcase compression, naturally aspirated two-cycle engines. In particular, the application is even narrower, being concerned principally with those engines of the spark ignition, gasoline burning type where a high bmep is desirable. The two principal exhaust systems considered are the diffuser and the expansion chamber. Both are analyzed experimentally and theoretically and presented as measured and digitally computed pressure-time diagrams in simulated and actual engine exhaust systems. These are compared and discussed.

Mathematical models of the open cycle gas exchange process and the closed cycle combustion process are developed for a Wankel engine. The theoretical model of the complete engine operating cycle is programmed for a digital computer and the results are shown for a small single rotor charge cooled Wankel engine. The predicted pressure diagrams in the working chamber and in the inlet, transfer and exhaust ducts are compared with measured values as is the predicted volumetric efficiency relationship with engine speed. The predicted charging efficiency relationship with engine speed is also compared with the measured brake mean effective pressure characteristic to demonstrate the usefulness of the theoretical model.

The theoretical modelling of the scavenge process for a naturally aspirated two-cycle engine is described and employed in conjunction with an unsteady gas dynamic analysis of flow in the engine ducting. Programmed for a digital computer, the results of this theoretical study are shown in relation to a 250 cm3 engine with values of predicted charging efficiency, scavenging efficiency, and delivery ratio given as a function of engine speed. These are compared with measured values of scavenging efficiency and the usual performance characteristics of power, mean effective pressure, delivery ratio, and specific fuel consumption. Also compared are the measured and predicted pressure diagrams taken in the cylinder, the crankcase, and the exhaust and inlet ducts. The design of a somewhat unique cylinder gas sampling valve of the mechanical type is described and its usage discussed both theoretically and practically.

Measurement of pressure-time histories in the exhaust system of a naturally aspirated internal combustion engine poses some difficult instrumentation problems. This paper describes an experimental and theoretical approach in tackling this research. The exhaust system is simulated by pulses of compressed air at a frequency of up to 4000 pulses/minute, that is, a 1 cyl 4 stroke cycle engine running at 8000 rpm. The pressure-time histories are calculated by digital computer in terms of the cylinder, exhaust valve, and pipe friction characteristics and compared with the experimental pressure-transducer records at various positions in the exhaust system.

Modern turbocharged diesel engines employ exhaust driven turboblowers operating at high speeds up to 100,000 rpm. The performance assessment of such units demands precise and controllable power absorption and torque measurements at these very high rotational speeds. Additionally the parameters, speed, mass flow, static and dynamic pressures and temperatures must be measured. The turbine power absorption and torque measutement present unique problems. The remaining parameters may present some difficulties but generally the problems are not so great. The design of a high speed dynamometer and the development problems encountered are described. The dynamometer has been used to establihs the performance characteristics of a C. A. V. 01 turbocharger and these are reported.

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.

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.

This paper presents a single-cycle gas simulation of the scavenging process in a two-stroke cycle engine. The apparatus used is described in the most detailed fashion and the experimental procedure is covered completely. On the apparatus is placed some eleven differing cylinders of a Yamaha 250 motorcycle engine and the scavenging efficiency - scavenge ratio characteristics of each determined experimentally. The results of these experiments are compared with the known performance characteristics of the same eleven cylinders which were obtained under firing conditions for variations of power, torque, air-flow, fuel consumption and scavenging efficiency at several speeds and throttle positions. The correlation, between the ranking of the several cylinders determined on the scavenging simulation apparatus with the performance characteristics obtained under firing conditions, is very good.

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.

The paper describes and lists the performance characteristics of a 400 cm3 single-cylinder two-stroke cycle engine with natural-aspiration, spark-ignition and carburetter control of gasoline fuel. The engine features an uncomplicated and unique system of stratified-charging which helps reduce the short-circuited loss of fuel during scavenging. With an untuned exhaust system the engine produces a peak power of 13 kW at 5500 rev/min and a brake specific fuel consumption which has a minimum of 0.265 kg/kWh but, more importantly, virtually the entire speed and load range is below 0.34 kg/kWh (0.55 lb/hp. hr). All performance characteristics at several throttle openings are presented at various engine speeds as a function of air/fuel ratio.

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.

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.

At the 1999 SETC meeting, a paper presented a simple, tuned and silenced exhaust system for a two-stroke engine which theoretically reduced both noise and exhaust emissions and increased engine power and fuel efficiency. In this paper that design concept is applied to a small 56 cc industrial engine and experimentally shown to deliver the projected behaviour which was predicted in that earlier publication. Experimental test results are presented for power output, fuel consumption, and exhaust emissions to illustrate these statements. An accurate engine simulation software package (VIRTUAL 2-STROKE) is employed to model the entire two-stroke engine and to demonstrate not only its effectiveness as a design tool in this area but also that it can accurately predict the above-mentioned performance and emission characteristics.

Previous papers published by the author have described unsteady gas flow through a naturally aspirated two-cycle engine and the most recent of these publications details a theoretical modelling of the gas exchange or scavenge process for the cylinder of this type of power unit. This results in the ability to predict the trapped charge state, mass, and purity characteristics. With such information it becomes sensible to apply a closed cycle thermodynamic analysis to it and to further predict directly power, torque, and fuel consumption characteristics. This paper describes such a simple closed cycle analysis and compares the theoretical results of power, mean effective pressure, specific fuel consumption, and cylinder pressure diagrams with corresponding measured data from two engines.

Earlier papers by the principal author in conjunction with others have described the prediction of noise and performance characteristics of two-cycle spark-ignition crankcase compression engines. These calculations are performed on a digital computer and are shown to simulate accurately the unsteady gas flow and thermodynamic processes in such power units. The engines described previously had induction control by the piston or with a disc valve. In this paper the work is extended to engines fitted with reed valves controlling intake air flow and examples illustrating the effectiveness of such calculations are presented. In particular, a single-cylinder industrial engine is employed to show clearly the effects of changing such parameters as reed petal thickness, stop-plate radii and numbers of reed petals on the performance characteristics.

This paper describes some of the experimental and theoretical work carried out at the Queen's University, Belfast in connection with a pulsejet project. It starts from the earliest stages of trying to achieve a working reed valved engine and continues to the present where valve less pulsejets have been designed with the aid of a simulation program. Suggestions are made regarding the manner in which various parameters such as duct and intake geometry, orientation and flight speed can affect performance. It suggests four main criteria which must be fulfilled for any valveless pulsejet to operate successfully and discusses methods by which these can be achieved.

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.