Single-cylinder 125 cc Stepped Piston Engine for Mobility and Portable Power Generation Applications a Azhar Abdul Aziz, b Zulkarnain Abdul Latiff, c Mohd Farid Muhammad Said & d Hishamuddin Mohd Jamil a Automotive Development Centre (ADC) Faculty of Mechanical Engineering Universiti Teknologi Malaysia Tel: (+607) 5535447 E-mail: azhar@fkm.utm.my b Automotive Development Centre (ADC) Faculty of Mechanical Engineering Universiti Teknologi Malaysia Tel: (+607) 5535447 E-mail: zkarnain@fkm.utm.my c Automotive Development Centre (ADC) Faculty of Mechanical Engineering Universiti Teknologi Malaysia Tel: (+607) 5535447 E-mail: mfarid@fkm.utm.my d Automotive Development Centre (ADC) Faculty of Mechanical Engineering Universiti Teknologi Malaysia Tel: (+607) 5535447 E-mail: mhisham@fkm.utm.my ABSTRACT Two-stroke engines is far simpler than four-stroke version from its physical perspective. For a given brake output, two-stroke is lighter, easier to work on, and provide higher power-to-weight ratio than the four-stroke, making it suitable for small platform applications. However a conventional two-stroke engine has a reputation for generating smoke and unburned fuel, a situation which does not meet many emissions regulations, now enforced around the world. Thus for many decades two- stroke engines were not favored, giving ways to four-stroke engines to dominate applications, especially for mobile power-generation purposes. In the quest to improve the potential of such an engine, a group of researchers from the Automotive Development Centre (ADC), Universiti Teknologi Malaysia (UTM) has come up with a 125 cc, air- cooled stepped-piston engine to demonstrate the higher power-to-weight ratio feature, apart from overcoming emission reduction. The engine is designed to mitigate the problem of mixture short circuiting, which is the major hindrance to combustion efficiency, and for this to happen they have incorporated a three-port stratification strategy onto the engine. This paper provides the overview related to the earlier work done to infuse the necessary features and highlights some of the performance features of this unique engine design. Keywords: Two-stroke, engine, stepped-piston, prototype, design 1. INTRODUCTION The basic two-stroke engine operates by compressing the air-fuel mixture both in the crankcase and the cylinder, and moves the mixture around by making use of the vacuum and pressure created by the piston movement. The engine performs all functions in two strokes of the piston, (down and up) and the spark plug fires each time the piston is about to approach the engine’s top dead centre (TDC). Valving is provided by the motion of the piston, sliding past port openings in the cylinder wall. The above four functions must be crowded into just two piston strokes. As the piston descends on the power stroke, at roughly half- stroke it begins to uncover a large exhaust port or ports, and exhaust gas begins to leave the cylinder. Approximately a quarter-stroke later, the piston will uncover a set of fresh-charge transfer ports. Fresh air and fuel have meanwhile been drawn into the crankcase, and the descent of the piston compresses this fuel-air mixture. As the transfer ports open, this mixture begins to jet into the cylinder through them.The problem that will arise are: even with the best-possible aiming of the transfer ports (keeping the entering fresh charge