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A three cylinder two-stroke cycle diesel engine is proposed for automotive use. The engine is of the simple loop or cross-scavenging type with a crosshead seal and under piston scavenging pump. This paper records the initial investigations of this concept using a purpose built single cylinder engine. Results from different combustion systems are presented together with tests with the same engine when using an external air supply. Measurements from a parallel investigation using a laser doppler anemometer to measure air swirl motion within one of the chambers are also presented.

The measurement of transfer port efflux velocities using laser doppler velocimetry (LDV) in a motored model two-stroke engine is described. The single cylinder engine used is of two port loop scavenged design, externally blown to provide scavenge flow into the cylinder during the entire port open period. LDV measurements were taken along a vertical path, central to the transfer duct, at the port exit over a range of crankangles at motoring speeds of 225rpm, 600rpm, and 900rpm. At 225rpm further measurements were taken for a range of delivery ratios from 0.7 to 2.0. Relatively uniform velocity profiles indicate plug like flow issuing from the port under most conditions. The resultant flow direction is seen never to align with the transfer duct walls, but to vary as a function of crankangle. Quantitative analysis of angles defining mean flow direction reveal that dynamic efflux behaviour is essentially similar for all tested speeds and delivery ratios.

Previous papers from The Queen's University of Belfast have shown the application of digital computers in simulating the unsteady gas flow and thermodynamic processes in single cylinder engines having various types of exhaust systems. This paper outlines the results of an investigation of twin cylinder engines of the outboard motor type where compact and complex exhaust systems are used to optimise the performance characteristics within a specified package size. Measured and predicted pressure-time histories for the exhaust and open cycle cylinder are presented for a 350cm3, twin cylinder test engine, which has been extensively modified to emulate the porting configuration and performance characteristics of two production outboard motor engines. Also compared are the measured and predicted output performance data for the engines, where all of the predicted data is produced by a new twin cylinder simulation program incorporating a simple constant pressure junction model.

The importance of exhaust system design for three cylinder two-stroke engines is demonstrated using a thermodynamic model developed at The Queen's University of Belfast. The influence of the major exhaust parameters on wide open throttle power and bmep is investigated. In addition, the potential benefits of reed valve induction over piston port induction at low engine speeds are demonstrated for one particular engine configuration.