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This paper describes predictive models and validation experiments used to quantify the in-chamber heat transfer of LiquidPiston’s rotary 70cc SI “XMv3” engine. The XMv3 engine is air cooled, with separate cooling flow paths for the stationary parts and the rotor. The heat transfer rate to the stationary parts was measured by thermal energy balance of that circuit’s cooling air. However, because the rotor’s cooling air mixes internally with the engine’s exhaust gas, a similar procedure was not practical for the rotor circuit. Instead, a CONVERGE CFD model was developed, and used together with GT-POWER to derive boundary conditions to estimate a ratio between rotor and stationary parts heat transfer, thus allowing estimation of rotor and total heat losses. For both cases studied (5000 and 9000 rpm under full load), the rotor’s heat loss was found to be ∼60% that of the stationary parts, and overall heat losses were less than 35% of supplied fuel energy.

The current study introduces a Variable Valve Timing (VVT) trapezoidal rotary valve for a 4-stroke spark-ignition engine. Being trapezoidal, enables the rotary valve to change the inlet and exhaust timing continuously, therefore allowing it to control the engine load without the need for a throttle valve. The geometry of the valve is studied in detail, calculating the intersection areas between the windows (ports) of the valve and those of the combustion chamber during the engine cycle. As the valve openings are trapezoidal and the opening of the combustion chamber is trapezoidal as well, there is a multitude of geometry variables that need to be optimized. During idle the engine needs to breathe through just a very small area, while during high load operation the opening needs to be generous. Finally, the trapezoidal rotary valve system is compared to a conventional VVT system.

Over-expansion is one of the promising strategies for improving Internal combustion engine (ICE) efficiency and emissions. It can be implemented by using an unconventional crankshaft. These mechanisms have mass production potential and acceptable friction losses, but also a complex kinematic and dynamic behaviour. This paper proposes such a crank design, a small planetary hypotrochoid over-expanded single cylinder engine - UMotor - and compares it to equivalent conventional ICEs with similar intake or expansion strokes. A suitable crankshaft counter weight geometry was determined in order to minimize the overall reaction forces. The mass balancing studies were conducted via a dynamic motion analysis of the crank drive, including a Fast Fourier Transform (FFT) frequency analysis. For the tested engine speeds, the UMotor average and peak magnitude reaction forces proved to be similar to those generated in the conventional engines for intermediate and high engine speeds.