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Simple heat transfer correlations are known to underpredict the single-phase convective heat transfer coefficient when applied to internal combustion (IC) engine cooling passages. The reasons for such underprediction were investigated using a specially designed test rig which was operated under a wide variety of test conditions relevant to IC engine operation. Data from this rig study identified that undeveloped flow (fluid dynamically and thermally), surface roughness and fluid viscosity variation with temperature were the physical reasons responsible for the mismatch. Simple empirical heat transfer models have subsequently been extended to take account of these factors and are shown to give much improved correlation with rig data, and data from an engine study. The implications of this work for predicting engine heat transfer in a three-dimensional computational fluid dynamics environment are discussed.

The Recuperated Split Cycle Engine is a new type of ICE, offering a step change in efficiency and tailpipe emissions. It targets the heavy duty, long-haul sector (trucks, off-highway, rail, shipping), where electrification is most challenging, and distributed generation, where capacity is required to support rising electrification. The engine separates cold (induction, compression) and hot (combustion, expansion) parts of the cycle; waste exhaust heat is recovered between them via a recuperator, as in a recuperated gas turbine. Recent research presented at this conference [1] shows that the sonic airflows seen in the induction event give rise to extraordinary fuel mixing and clean, cool combustion, with potential for after-treated emission levels between SULEV and zero-impact (either unmeasurable or below ambient). Recuperation and thermal insulation of the hot cylinder (both feasible within the capability of common materials) also enable high thermal efficiency, with a flatter efficiency map than a conventional ICE. Combining the two attributes, and introducing sustainable fuels, places this readily manufactured, affordable technology on a par with battery-electric and fuel cell propulsion. Results from simulation to optimise the concept are described. A Ricardo WAVE model was built, with validation of key inputs such as valve breathing, heat transfer and burn-rates from relevant experimental research data. The model was used to develop the cycle around three conceptsa basic layout, "ThermoPower", was shown to be capable of over 10% fuel saving; "Wet ThermoPower" uses water injection as a compression coolant for greater efficiency, while the ultimate "CryoPower" injects Liquid Nitrogen for quasi-isothermal compression and charge dilution. The optimisation process and practical details are described, especially the development of the critical recuperator, which is subjected to high pressure and temperature; management of its thermal expansion and manufacturing process have been optimised to minimise add-cost over a current ICE bill of materials.

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