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.
Highlights
Natural gas (NG) is considered as one of the three main sources of energy along with coal and oil and plays an essential role in the world’s energy supply
It can be explained that too lean a mixture and a smaller pilot diesel injection slow down the burn rate and most of the NG-air mixture is burned in the post-combustion period during the expansion stroke as the instantaneous heat release rate (HRR) trace expresses the same phenomenon with increasing substitution rate [26]
The substitution rate can reach as high as 40% and the reduction of power output is controlled at 5.7% less than the target power requirement with throttled control
Summary
Natural gas (NG) is considered as one of the three main sources of energy along with coal and oil and plays an essential role in the world’s energy supply. Thanks to the merit of high intrinsic H/C ratio, high auto-ignition temperature and superior resource availability at attractive prices, NG is widely recognized as one of the most promising clean alternative fuels for conventional diesel engines. The usage of NG dual-fuel diesel engines retrofitted from diesel engines has been focused on to improve fuel economy and reduce exhaust gas emissions [1,2,3]. The diesel fuel supply system remains unchanged and provides the pilot diesel to ignite the NG-air mixture in the combustion chamber. For reasons of both emissions and fuel economy, the main purpose of development of NG dual-fuel diesel engines is to maximize the use of cheaper
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