Fuel Injection for Low Emission 50cc 2-Stroke Scooter

Abstract

The ideal attributes of light weight, low cost and high power density have made the 2-stroke engine unrivalled in the scooter and moped market for many years. However, the challenges of meeting new emissions regulations, especially the latest Euro III emission test cycle have reduced the 2-stroke's dominance and it is now often considered to be too dirty and inefficient to have a future. As a result its product placement is on the decline. This paper introduces and discusses the latest application of a low-cost high-frequency injection system (Pulse Count [1,2]) to both the fuel flow and lubrication oil flow of a 2-stroke scooter; allowing both fluids to be individually mapped and optimised for the complete engine operating range. This in turn enables the 2-stroke engine to pass the latest Euro III test whilst improving the fuel economy by a considerable margin, without changing the architecture of the engine. Examples of the latest developments of a highly integrated engine management system, including fuel and oil injector technology are shown. The paper draws conclusions from the test results showing the clear benefits of electronic fuel injection both for emissions and fuel consumption, and demonstrates that these benefits are achievable from a compact well integrated throttle body unit suitable for the small 2-stroke engine market. INTRODUCTION: 2-STROKE MOTOR APPLICATIONS, CONCERNS AND FUTURE POSSIBILITIES Although the 4-stroke engine has replaced 2-stroke engines in markets where emission legislation has been brought in force, there are still many applications where the light weight and low cost benefits of the 2-stroke engines are so significant as to make them irreplaceable. The lower powered, heavier and more costly 4-stroke engine replacement would severely compromise the function and/or performance of the end product. Examples Page 2 of 14 of these applications are the chainsaw, small outboard motor and limited capacity 'moped' or scooter, where maximum power from a very small, lightweight and low cost engine is paramount. Examples are shown in Figure 1. Figure 1 Examples of applications requiring the lightweight power of a 2-stroke engine However, even in these specialised areas there is a necessity to meet new clean emission standards and reduce fuel consumption (CO2 emissions) in line with environmental trends. It is therefore essential that full electronic control of the 2-stroke engine is applied in order to fully optimise the combustion and performance of these small engines and ensure compliance with future standards. Table 1 shows the historic emissions regulation limits for 2-stroke mopeds and the proposed new limits coming into force in 2012. Table 1 Emission limit trend for 50cc mopeds. Stages Emission limits for type approval and conformity of production for Mopeds Test cycle CO (g/km) HC + NOx (g/km) 1999 (EURO 1) 6.0 3.0 UN-ECE Reg.47 2002 (EURO 2) 1.0 1.2 UN-ECE Reg.47 2012 (EURO 3) 1.0 1.2 UN-ECE Reg.47 Hot and Cold Cycles Previous work has been done showing the dramatic reduction in emissions that can be achieved with 2-stroke engines using Direct Injection of the fuel into the combustion chamber [3,4,5] and this technology is often applied to high end expensive 2-stroke engines such as high performance outboard motors and jet skis. However, this solution while technically applicable to the smaller engines carries with it a high on-cost and complexity which has prevented it from large scale application in the low cost markets.