Abstract
In order to reduce the heat loss and improve the indicated thermal efficiency of hydrogen-enriched compressed natural gas engines, this article presents a combination of Atkinson cycle with high compression ratio and low heat rejection on the hydrogen-enriched compressed natural gas prototype engine with 55% hydrogen blend. The combustion characteristics and energy distribution of the prototype and modified engines were investigated by simulation, and the conclusions are as follows: the pressure and temperature of modified engines are higher than those of the prototype during the combustion process. Compared with the prototype, the modified engines present lower peak heat release rate, but faster combustion after ignition, and their CA50 are closer to top dead center. Although the high compression ratio engine with Atkinson cycle generates more heat loss, its indicated thermal efficiency still increases by 0.6% with the decrease in the exhaust energy. Furthermore, the high compression ratio engine with low heat rejection and Atkinson cycle combines the advantages of low heat loss and relatively longer expansion stroke, so its heat loss reduces obviously, and 61.6% of the saved energy from low heat rejection and Atkinson cycle can be converted into indicated work that indicates a 4.5% improvement in indicated thermal efficiency over the prototype, which makes it perform better in terms of power and fuel economy simultaneously.
Highlights
In the current background of green, environmental protection, low carbon and sustainable development, energy saving and emission reduction are the urgent issues facing the automobile industry all over the world
The results show that the heat loss of the compressed natural gas (CNG) engine increases after blending hydrogen, but it decreases with the increase in the excess air ratio (l), which is in line with the results in the literature.[14,15,16]
If the Atkinson cycle and low heat rejection (LHR) technology are combined on HCNG engines, heat loss would be reduced and more energy may be transformed to indicated work, the indicated thermal efficiency (ITE) of HCNG engines can be further improved
Summary
In the current background of green, environmental protection, low carbon and sustainable development, energy saving and emission reduction are the urgent issues facing the automobile industry all over the world. If the Atkinson cycle and low heat rejection (LHR) technology are combined on HCNG engines, heat loss would be reduced and more energy may be transformed to indicated work, the indicated thermal efficiency (ITE) of HCNG engines can be further improved.
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