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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.

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.

One-dimensional (1-D) unsteady gas dynamic models of a number of common muffler (or silencer) elements have been incorporated into a1-D simulation code to predict the impact of the muffler on the gas dynamics within the overall system and the radiated Sound Pressure Level (SPL) noise spectrum in free-space. Correlation with measured data has been achieved using a Single-Pulse rig for detailed unsteady gas dynamic analysis and a Rotary-Valve rig in conjunction with an anechoic chamber for noise spectra analysis. The results obtained show good agreement both gas dynamically and acoustically. The incorporation of these models into a full 1-D engine simulation code should facilitate the rapid assessment of various muffler designs prior to prototype manufacture and testing.

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.

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.

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.