Environmental consciousness and tightening emissions legislation push the market share of electronic fuel injection within a dynamically growing world wide small engines market. Similar to automotive engines during late 1980's, this opens up opportunities for original equipment manufacturers (OEM) and suppliers to jointly advance small engines performance in terms of fuel economy, emissions, and drivability.
In this context, advanced combustion system analyses from automotive engine testing have been applied to a typical production motorcycle small engine. The 125cc 4-stroke, 2-valve, air-cooled, single-cylinder engine with closed-loop lambda-controlled electronic port fuel injection was investigated in original series configuration on an engine dynamometer. The test cycle fuel consumption simulation provides reasonable best case fuel economy estimates based on stationary map fuel consumption measurements. For Indian Driving Cycle (IDC) it yielded roughly 1.4l/100km, for World Motorcycle Test Cycle (WMTC) 1.8l/100km. The thermodynamic split of losses analysis of test-cycle relevant operating points provides deeper physical insight into engine physics and reveals optimization potential. Namely, full load and low load enrichment increase fuel consumption, particularly at high engine temperatures. At colder engine, the ignition system is not capable to maintain an efficiency-optimal combustion phasing and the engine roughness increases. Such findings shall promote the development of customized single components and complete modular systems for 2-wheelers.
