Development of a hydrostatic test bench to characterize mechanical losses of low power internal combustion engines under controlled lubricant and coolant temperature conditions

Experimental testing of internal combustion engines is essential for evaluating mechanical performance, developing engine components, assessing surface coatings, formulating lubricants and friction modifiers, and validating predictive friction models. This work presents the development and integration of a test bench for low-power engines, based on a hydrostatic loading system, to characterize mechanical losses under controlled conditions of engine speed, load, lubricant temperature, and coolant temperature. The tested engine is a liquid-cooled single-cylinder spark-ignition motorcycle engine, whose design couples a five-speed gearbox to the engine crankshaft by means of a multi-disc clutch. The test bed is equipped with two independent thermal management circuits: one for heating, cooling, and circulating the lubricant, and another for supplying cold coolant to the engine. The instrumentation and data acquisition system are described in detail. Initial results from the test bench are presented, including instantaneous curves and three-dimensional maps of mean effective and indicated parameters, mechanical losses, and pumping losses.