Search Results

This paper describes an experimental comparison of loop and cross scavenged single-cylinder research engines. The cross scavenged engines have employed the QUB type deflector piston. The initial results show that the QUB cross scavenged engine exhibited inferior performance characteristics. Utilizing the QUB single cycle test rig, a study of the QUB cross scavenging system has shown that the bore-to-stroke ratio significantly influences the scavenging behaviour; reduction of the bore-to-stroke ratio from over-square values gave improved characteristics. On the basis of this finding, a new cross scavenged cylinder barrel was designed. In a subsequent series of dynamometer tests, improvements in power, fuel economy and emission characteristics were recorded for the new cylinder. These improved results approximate closely to those recorded for the loop scavenged engine and are considerably superior to those of the original cross scavenged cylinder.

This paper outlines some developments in engine modelling techniques and details the results of an extensive validation exercise. This validation was conducted in two distinct parts: firstly, on a specially constructed rig, and, secondly, using engine test results. The test rig described was constructed in such a way as to rigourously test the theories employed. Comparisons were made between measured and predicted pressure traces and air mass flow. The predicted results are shown to be in good agreement with all measurements recorded. The performance of a complete engine simulation is also described and compared with actual dynamometer test results. The accuracy of this model is clearly demonstrated for all engine performance parameters.

This paper presents a unique empirical approach for the design dimensioning of the valving and the ducting of a high performance, naturally aspirated, spark-ignition automotive engine so as to attain the required performance levels at a given engine speed. The contentions behind these several empirical criteria are checked out, firstly by analysing the geometry of a number of famous racing engines and, secondly, systematically testing each element of the empirical criteria using an engine simulation model of an actual and well-optimised, four-cylinder high performance engine. The use of detailed empirical theory for this purpose permits the designer to more rapidly optimise racing engines by entering data into an engine simulation model in a logical manner with data which is already well-matched empirically before so doing.

Historically, when valve springs were wound with round wire and the coils were nominally equally spaced, it was relatively easy for the engineer to calculate the virtually-linear load carrying capacity, the almost non-varying stiffness and the relatively-constant natural frequency of the spring. This was the design data that was required then for some simplistic but effective calculations of the valvetrain dynamic stability. In recent times, valve springs have come to be commonly wound with other wire sections such as ovate and with coil-coil spacings that are unequal, giving the spring a variable load carrying capacity, variable stiffness and a variable natural frequency with deflection. Such springs are known as progressive wound springs. The computation of these spring characteristics is no longer a simple matter and neither is their incorporation within the calculation of the dynamic stability of the entire valvetrain. The technical literature is very sparse on these topics.

A Yamaha YZ400, 5-valve, 4-stroke cycle, motocross racing, motorcycle engine is instrumented to provide pressure diagrams in the exhaust system which are recorded over the usable engine speed range at full throttle from 5000 rpm to 11000 rpm. The engine produces a maximum of some 34 kW (46 hp) power output. The production muffler-ended exhaust system is replaced with two alternative and more highly-tuned exhaust systems, namely a straight pipe and a straight pipe and diffuser. The complete engine geometry together with these two exhaust systems is simulated using an engine simulation software package (VIRTUAL 4-STROKE) and the experimentally-recorded exhaust pressure diagrams and performance characteristics of power, torque, etc., are compared with the predictions of the theoretical simulation. The variation of exhaust system produces differing performance characteristics whose origins the measured pressure diagrams and recorded performance characteristics struggle to explain.

This paper reports on the experimental evaluation of the coefficient of discharge of ports in the cylinder wall of a two-stroke engine and of restrictions within engine ducting. It is required to know such discharge coefficients, as a function of the area of the restriction and the pressure ratio across it, so that in the mathematical modelling process at each juncture during the open cycle, accuracy can be obtained for the mass flow rates of gases, the magnitude of pressure waves created, and the effect on the internal engine thermodynamics. The discharge coefficients, Cd, are required for both inflow and outflow, i.e in both directions, at all such cylinder apertures or ducting restrictions. A fundamental experimental study is conducted of the effect of size of the engine ducting on the discharge coefficient of the cylinder porting aperture and it is found to have no significant influence. The general applicability of this conclusion in design and simulation practice is debated.

Anaerobic digestion is a popular method of treating sewage sludge. Biogas or sewage gas is a by-product of this process. Significant volumes of biogas are produced at many sewage treatment works and also at some landfill sites from the natural breakdown of municipal waste. This biogas can be used as a fuel for an engine and generating set, producing electrical power and heat. A multi-cylinder two-stroke cycle system, capable of being retrofitted to current production four-stroke cycle engines, is proposed, primarily for the combustion of biogas in combined heat and power applications. The engine incorporates features to give good tolerance to the corrosive agents associated with biogas. This paper describes the design and initial development of a purpose built single cylinder research engine to investigate this concept. A low pressure direct injection system which has been developed for use with the engine is also outlined.

Over recent decades many studies have emanated from The Queen's University of Belfast (QUB) regarding the modelling of the performance characteristics of the reciprocating internal combustion engine by following the unsteady gas flow in the ducting and through the cylinder. More recently, the author has published an ‘alternative’ method of modelling the unsteady flow in the engine ducting together with experimental proof of its accuracy for the simulation of two- and four-stroke cycle engines. Not only does the new model impose mass flow continuity at all sections of an engine and its ducting, but it is fully non-isentropic in its handling of friction, heat transfer and area changes along any duct. This paper presents a non-isentropic model of flow at a three way branch in a duct, which model expands significantly on previous theoretical approaches from QUB by its capabilities in dealing with mixtures of gases travelling through the branch.

Pressure-time diagrams taken near the exhaust port of a 2-cycle engine provide valuable insight into the performance of the power unit. The optimum phasing of the scavenging and plugging pulses are then observable from these diagrams. Unsteady flow gas dynamic theory, with the arithmetic handled by a digital computer, will predict the phasing and amplitude of these important exhaust pulse reflections at any engine speed, in any exhaust system, for any engine. Design of such an exhaust system for a projected engine unit or an existing design becomes a real possibility, thus saving valuable development time and money.

At The Queen's University of Belfast there has been, for some twenty years, a continuing program of research into scavenging flow in two-stroke cycle engines, recently using a single-cycle gas scavenging apparatus. This apparatus has been demonstrated to give accurate assessments of the scavenging efficiencies of such engine cylinders. The apparatus utilises a constant volume, isothermal flow process in the experimental simulation of the scavenging flow and, as many of the classic theories of scavenging are similarly formulated, this provides a unique opportunity to compare theory and experiment on the basis of equality of procedure. This paper presents experimental data for the scavenging characteristics of uniflow-, loop-and cross-scavenged two-stroke engine cylinders and compares the measurements with the classic theories of scavenging as presented by others in the literature.

The paper discusses the design of a racing motorcycle engine to compete in World Superbike racing. This class of motorcycle racing is based on production machines with four-stroke engines only. The rules allow three engine variants to be used, a 750 cm3 four-cylinder engine, a 1000 cm3 twin-cylinder engine, and a 900 cm3 three-cylinder engine. To date only the first two variations have been employed but this paper shows that the 900 cm3 engine has the highest potential power output of the set. This is demonstrated using engine simulation software and the finest detail of the design of the engine and its ducting are supplied within the discussion. The input data for the engine simulation is provided by empiricism so that the design is initially well-matched from the intake bellmouth to the end of the exhaust system. The outcome of this empirical process is confirmed by the engine simulation to be a relevant initial design procedure.

The paper discusses briefly the development of the theory of unsteady gas flow from a position of being totally misunderstood from the turn of this century until the 1940's, developed in the 1950's, and from which juncture the advent of the digital computer has turned such theory into a comprehensive design tool by the present day. While the most extensive use of this design method is for engines with a high performance specification, its employment as a design tool for industrial engines has been largely ignored. In the paper, a design for a small generating set engine at 3600 rpm is examined in great detail and the use of pressure wave effects is shown to enhance the engine performance considerably, either in terms of power gain, reduction of fuel consumption, reduction of hydrocarbon emissions, or reduction of noise levels.

This paper describes an inertial dynamometer system which has been applied to the testing of small two-stroke kart racing engines. The dynamometer incorporates a flywheel of appropriate moment of inertia to simulate the mass of a kart and driver. The test procedure involves measurement of the flywheel speed during an acceleration phase resulting from opening the throttle. Calculation of the instantaneous flywheel acceleration corresponding to each engine speed directly gives a measure of the torque and power characteristics. Performance results, including exhaust pressure traces, are presented from a series of tests conducted on a 100 cm3 kart engine. The results are compared with corresponding steady state measurements recorded on an eddy current dynamometer. In addition, the measured results are compared with predictions from a computer simulation.

Design and Simulation of Two-Stroke Engines is a unique hands-on information source. The author, having designed and developed many two-stroke engines, offers practical and empirical assistance to the engine designer on many topics ranging from porting layout, to combustion chamber profile, to tuned exhaust pipes. The information presented extends from the most fundamental theory to pragmatic design, development, and experimental testing issues. Chapters cover: Introduction to the Two-Stroke Engine Combustion in Two-Stroke Engines Computer Modeling of Engines Reduction of Fuel Consumption and Exhaust Emissions Reduction of Noise Emission from Two-Stroke Engines and more

This book provides design assistance with the actual mechanical design of an engine in which the gas dynamics, fluid mechanics, thermodynamics, and combustion have been optimized so as to provide the required performance characteristics such as power, torque, fuel consumption, or noise emission.