On the measurement and modelling of high pressure flows in poppet valves under steady-state and transient conditions

Flow coefficients of intake valves and port combinations were determined experimentally for a compressed nitrogen engine under steady-state and dynamic flow conditions for inlet pressures up to 3.2 MPa. Variable valve timing was combined with an indexed parked piston cylinder unit for testing valve flows at different cylinder volumes whilst maintaining realistic in-cylinder transient pressure profiles by simply using a fixed area outlet orifice. A one-dimensional modelling approach describing three-dimensional valve flow characteristics has been developed by the use of variable flow coefficients that take into account the propagation of flow jets and their boundaries as a function of downstream/upstream pressure ratios. The results obtained for the dynamic flow cases were compared with steadystate results for the cylinder to inlet port pressure ratios ranges from 0.18 to 0.83. The deviation of flow coefficients for both cases is discussed using pulsatile flow theory. The key findings include: 1. For a given valve lift, the steady-state flow coefficients fall by up to 21 percent with increasing cylinder/manifold pressure ratios within the measured range given above; 2. Transient flow coefficients deviated from those measured for the steady-state flow as the valve lift increases beyond a critical value of approximately 0.5 mm. The deviation can be due to the insufficient time of the development of steady state boundary layers, which can be quantified by the instantaneous Womersley number defined by using the transient hydraulic diameter. We show that it is possible to predict deviations of the transient valve flow from the steady-state measurements alone

Performance of a novel liquid nitrogen power system

In this article, we examine the hybridisation of refrigerated commercial vehicles through replacing the traditionally used auxiliary diesel engine with a non-polluting, non-electric unit as an effective emissions reduction alternative. The zero-emission hybrid solution presented in this article is a Liquid Nitrogen (LN2) engine system, featured with a novel integrated Heat Exchange Fluid (HEF) subsystem, that can provide simultaneous cooling and auxiliary power in, for example, refrigerated trucks. Evaporation of LN2 provides the cooling/refrigeration power. The resulting high pressure gaseous N2 then expands in the engine, producing shaft power. A major contribution of this research is the use of a novel direct in-cylinder HEF supply technology which we show experimentally that it leads to reliable and significantly enhanced engine performance. Specifically, a detailed experimental investigation into the effects of HEF temperature and flow rate at different inlet N2 conditions and engine speeds on engine performance is presented. Results from a thermodynamic analysis, based on an idealised cycle, are also presented to better understand the engine performance and assess the potential of the proposed engine architecture. The results show up to 41% brake thermal efficiency and up to 172 kJ/kg-LN2 specific work from the engine system, which are significantly higher figures when compared to previously reported maximum values in the literature (i.e. 9.2% and 40 kJ/kg-LN2, respectively). It is also shown that the thermodynamic model can predict with good accuracy the upper and lower limits of the measured indicated power and efficiency