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As the most advanced fuel injection system, the common rail system can achieve the flexible control of injection pressure, injection timing and injection rate. Thus, the pressure control strategy of high-pressure common rail system (HPCRS) will be critical for the performance of the diesel engine, as it affects its injection characteristics. In this paper, model in loop (MIL) simulation studies were carried out, a high-precision common rail hydraulic model and analytical rail pressure control strategy based on flow continuity equation were established. The delay of the high-pressure pump was accounted for and included in the proposed strategy, making it more targeted for HPCRS. The delay can be extremely important for high-pressure common rail overshoot especially in variable working condition. Next, the proposed strategy was compared to the traditional PI-based control strategy in both the start-up and transient conditions. Results indicated that the proposed strategy performs better regarding the overshoot, notably improving the control effect (compared to traditional PI-based strategy). The advances of using the proposed strategy primarily include improvements in working conditions with the obvious change in cycle injection quantity and engine speed. Both the proposed control strategy and PI-based strategy can track pressure effectively in various working conditions. [ABSTRACT FROM AUTHOR]

To explore the influence mechanism of initial turbulence on propagation speed of wrinkled flames, the turbulent combustion behavior of wrinkled stoichiometric hydrogen premixed flames was studied in a spherical fanstirred closed vessel under standard temperature and pressure. The variations on flame structure were first observed; turbulent flames first were distorted and then became cellular, and both first and second critical flame radii of cellularity declined with a increased rate as turbulent intensity rose. Then, the variations of stretch effects were compared to laminar flame; the global stretch rate on turbulent flame at a same flame size was raised while the enhancement extent was obviously enlarged with the increase of initial turbulent intensity and/or the growth of flame size. Finally, the variation regulations of propagation speed induced by varying turbulent intensity were analyzed; the nexus between propagation speed and initial turbulence was discussed with the considerations of cellularity phenomenon and stretch effects. [ABSTRACT FROM AUTHOR]

The macro characteristics and configurations of induced shock waves of the supersonic sprays are investigated by experimental methods. Visualization study of spray shape is carried out with the high-speed camera. The macro characteristics including spray tip penetration, velocity of spray tip and spray angle are analyzed. The configurations of shock waves are investigated by Schlieren technique. For supersonic sprays, the concept of spray front angle is presented. Effects of Mach number of spray on the spray front angle are investigated. The results show that the shape of spray tip is similar to blunt body when fuel spray is at transonic region. If spray entered the supersonic region, the oblique shock waves are induced instead of normal shock wave. With the velocity of spray increasing, the spray front angle and shock wave angle are increased. The tip region of the supersonic fuel spray is commonly formed a cone. Mean droplet diameter of fuel spray is measured using Malvern's Spraytec. Then the mean droplet diameter results are compared with three popular empirical models (Hiroyasu's, Varde's and Merrigton's model). It is found that the Merrigton's model shows a relative good correlation between models and experimental results. Finally, exponent of injection velocity in the Merrigton's model is fitted with experimental results. [ABSTRACT FROM AUTHOR]