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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.

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.

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.

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.

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.

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.

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.

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.

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.

A three dimensional computational fluid dynamics program is used to simulate theoretically the scavenging process in the loop-scavenged two-stroke cycle engine. The theoretical calculation uses the k - ε turbulence model and all calculations are confined to the in-cylinder region. The calculation geometry is oriented towards five actual engine cylinders which have been tested under firing conditions for the normal performance characteristics of power, torque, and specific fuel consumption. The same five engine cylinders have also been experimentally tested on a single-cycle gas testing rig for their scavenging efficiency - scavenge ratio characteristics. The ranking of the cylinders in order of merit in terms of scavenging efficiency by both the rig and the theoretical calculations is shown to be in good agreement with the evidence provided by the actual firing engine test results.

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.

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.

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.

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.

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.

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.

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.

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.

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.