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The goal of hydrogen engine research is to achieve highest possible efficiency with low NOx emissions. This is necessary for the hydrogen car to remain competitive with the ever-improving efficiency of conventional fuel's use, to take advantage of the increased availability of hydrogen distribution for fuel cells and to achieve better range than battery electric vehicles. This paper examines the special problems of hydrogen engine combustion and ways to improve efficiency. Central to this are the effects of compression ratio (CR) and lambda (excess air ratio) and ignition system. The results demonstrate highest indicated thermal efficiency at ultra lean condition of lambda ≻ 2 and with central ignition. This need for this lean mixture is partly explained by the higher heat transfer losses.

The mathematical equations describing the momentum, energy and mass exchanges in non-firing engine cylinders are described and solved. Attention is confined to laminar flow in axi-symmetric cylinders. Pressure development and velocity prediction, for plane cylindrical combustion chambers, compare favourably with experimental measurements for compression] and expansion in motored engines. At engine speeds less than 100 rev/min the piston motion induces a toroidal vortex during compression whose direction is not reversed on expansion. Conductive heat transfer at higher engine speeds, 600-1000 rev/min, adequately describes the gas-wall heat-transfer. Flow patterns are also predicted for a diesel-type bowl in piston configuration.

This paper presents experimental and computational results obtained on an in line, six cylinder, naturally aspirated, gasoline engine. Steady state measurements were first collected for a wide range of cam and spark timings versus throttle position and engine speed at part and full load. Simulations were performed by using an engine thermo-fluid model. The model was validated with measured steady state air and fuel flow rates and indicated and brake mean effective pressures. The model provides satisfactory accuracy and demonstrates the ability of the approach to produce fairly accurate steady state maps of BMEP and BSFC. However, results show that three major areas still need development especially at low loads, namely combustion, heat transfer and friction modeling, impacting respectively on IMEP and FMEP computations. Satisfactory measurement of small IMEP and derivation of FMEP at low loads is also a major issue.