Experimental Study on the Effects of Air Supply Control on Combustion and Emissions Performance at Medium and Low Load for a Dual-Fuel Diesel Engine

Abstract

Lowering the amount of excess air is believed to increase the density of the air-fuel mixture and help improve the combustion rate for compression ignition engines. This paper proposes an approach of adding a throttle body at the intake pipe to control the excess air ratio with reduction of air supply to achieve a better balance between the power, emissions and fuel efficiency at medium and low load of a natural gas dual-fuel diesel engine converted from a conventional diesel engine. Various experiments in both pure diesel and dual-fuel mode under intermediate engine speed are performed with the proposed critical method of excess air ratio control. The experimental results reveal that better excess air ratio is very beneficial for the power output and brake specific energy consumption in dual-fuel combustion under medium and low load conditions. Moreover, the substitution rate can reach as high as 40% under low load conditions with throttle control.

Effects of Injection Timing on Combustion and Emission Performance of Dual-Fuel Diesel Engine under Low to Medium Load Conditions

“…The varying BSEC for various operating conditions at low load and medium load are shown in Figures 7 and 8, respectively. Under the low-load condition and 40% SR, the engine BSEC dropped to 16.34 MJ/kWh when the DIT shifted to 27 • CA BTDC, which was 13.33% lower than the BSEC value measured in the pure diesel mode with the DIT of 17 • CA BTDC [9]. Similarly, the BSEC reduced by 11.73% when the DIT increased to 25 • CA BTDC under the medium-load condition and 80% SR compared to the corresponding BSEC value in the pure diesel working condition.…”

“…Energies 2019, 12, x FOR PEER REVIEW 9 of 14 which was 13.33% lower than the BSEC value measured in the pure diesel mode with the DIT of 17 °CA BTDC [9]. Similarly, the BSEC reduced by 11.73% when the DIT increased to 25 °CA BTDC under the medium-load condition and 80% SR compared to the corresponding BSEC value in the pure diesel working condition.…”

“…The fuel supply strategy based on excess air ratio control was previously described in detail [9]. In the pure diesel mode, low (27.1 N•m) and medium (50.6 N•m) loads at the target speed were selected as the target operating conditions.…”

“…However, controlling the air intake flow by adjusting the throttle valve can increase pumping losses, leading to a decrease in volumetric efficiency [8]. In the previous study, the authors installed a throttle body on the original intake pipe of the diesel engine to control the air flow and to study the effects of different NG substitution rates (SR) on the performance of an engine working in the dual-fuel mode under low to medium load conditions [9]. Fuel supply strategies based on excess air and air/fuel ratio control effectively reduce NO x emissions and work well with SR reaching 40% under low-load conditions and 80% under medium-load conditions, which attained an acceptable improvement of the SR since no more than 30% of NG mass percentage is suggested by previous studies without throttle control at low load [10].…”

“…Under the requirement of minimum retrofit on the engine provided by the cooperative enterprise, our previous work examined that it was possible for the target engine working under low to medium load conditions to achieve a higher SR and to reduce nitrogen oxide (NO x ) emissions by controlling the excess air ratio, without the support of EGR and turbocharger [9]. However, as the SR increases, increasing CO and HC emissions become salient.…”