Experimental investigation of hydraulic effects of two-stage fuel injection on fuel-injection systems and diesel combustion in a high-speed optical common-rail diesel engine

Abstract

The final, definitive version of this paper has been published in International Journal of Engine Research, Vol 15 Issue 1, September 2012, ppublished by SAGE Publishing, All rights reserved.In order to meet the ever more stringent emission standards, significant efforts have been devoted to the research and development of internal combustion engines. The requirements for more efficient and responsive diesel engines have led to the introduction and implementation of multiple injection strategies. However, the effects of such injection modes on the hydraulic systems, such as the high-pressure pipes and fuel injectors, must be thoroughly examined and compensated for since the combustion and the formation of pollutants in direct-injection engines are directly influenced by the spatial and temporal distribution of the injected fuel within the combustion chamber. This study investigated the hydraulic effects of two-stage fuel injection on diesel combustion and emissions. The fuel-injection system was characterised for all the tested strategies through the measurement of the fuel-injection rate and quantity. In particular, the interaction between the two injection events was identified. The effects of two-stage injection, dwell angle and the interactions between two consecutive injection events on the combustion process and the emissions were investigated in a high-speed direct-injection single-cylinder optical diesel engine using heat-release analysis and high-speed fuel spray and combustion visualisation techniques. The results indicated that the two-stage injection strategy has the potential for simultaneous reduction of nitrogen oxide, soot and unburned hydrocarbon emissions. The results suggested that an optimum fuel quantity in the first injection exists, 0???30%, with which simultaneous reduction of nitrogen oxide, soot and unburned hydrocarbon emissions can be achieved with the added benefits of improved engine performance, fuel economy and combustion noise. However, higher soot emissions were produced, mainly due to the interaction between the two consecutive fuel-injection events whereby the fuel sprays during the second injection were injected into burning regions, as well as reduced soot oxidation due to the continuation of the combustion into the expansion stroke

Experimental investigation into the effects of two-stage injection on fuel injection quantity, combustion and emissions in a high-speed optical common rail diesel engine

“…It is important to note that there exists a time lag between the start of the injector current waveform and the start of fuel injection due to the inertia of the system as illustrated in Figure 4. The authors have previously reported on the hydraulic effects of two-stage injection on fuel injection quantity, combustion characteristics and emissions [24,25]. It was identified that the fuel injection quantity during the second injection was substantially influenced by the first injection when they were closely spaced in time.…”

“…The fuel injection rate profiles of the twin and variable split fuel injection strategies are presented in Figure 5. It should be noted that the twin split injections were obtained with the same energising time for the first and second injections and the difference in the fuel injection quantity in the second injection was mainly attributed to the design limitations of the injector utilised as well as the adverse effects of pressure waves in the high pressure fuel line, caused by the first injection [24,25]. Consequently, the FIE was thoroughly calibrated and the second fuel injection pulse width was optimised such that the quantity of fuel injected during the second injection was identical to that of the first injection, Figure 5 and Table 5.…”

“…In addition, interference between injections could also be identified for two-stage or multiple injections, whereby substantial variations in the quantity and rate of fuel injection could be experienced. Detailed explanation of the experimental setup/procedure can be found in [24,25].…”

“…Although, hydraulic effects of two-stage fuel injection has been previously reported [10,[19][20][21][22][23][24][25], the effects of advanced fuel injection modes on the fuel injection system are yet to be fully explored and few detailed in-cylinder studies have been carried out on the interaction of two-stage fuel injection and its effect on fuel injection quantity, combustion characteristics and exhaust emissions. The objective of this study was to investigate the effects of fuel injection equipment (FIE) characterisation and optimisation on diesel combustion and emissions with two-stage fuel injection.…”

Simultaneous imaging of diesel spray atomisation and evaporation processes in a single-cylinder CR diesel engine

“…In order to obtain the gain curves of the injector utilised, injection rate and quantity of single injection strategies as a function of injection pulse width and injection pressure were experimentally evaluated using a FIE calibration test rig based on Zeuch's method presented by Ishikawa et al [34]. Detailed explanation of the experimental setup/procedure can be found in [35,36]. Several single injection strategies with different injection duration were tested at the injection pressure of 1200 bar in order to evaluate the fuel injection quantity as a function of injection pulse width, Figure 6.…”