Abstract
A micro-reciprocating piston internal combustion engine with liquid hydrocarbon fuel has the potential to supply ultrahigh density energy to micro electro mechanical system because of its high-density energy, simple structure, and mature energy conversion principle. However, the diagnostic test of the combustion characteristics of the micro reciprocating piston internal combustion engine shows that its combustion characteristics are poor, and the combustion rate was lower with the combustion duration of more than 50 °CA. The mean indicated pressure (Pmi) value was only 0.137 MPa, the combustion stability was very poor, and the cycle variation rate of the Pmi was up to 60%. To improve its combustion performance, the method to enhance combustion in micro-space is explored then. Mechanism studies have shown that the pyrolysis reaction of nitromethane and hydrogen peroxide can produce amounts of free radicals OH, with the possibility of improving the combustion of methanol. Therefore, a method for adjusting the composition of methanol fuel to enhance combustion is proposed, and the method is theoretically confirmed. Finally, based on this method, the test was carried out. The results showed that the combustion rate increased and the combustion duration decreased by 6% after adding nitromethane. The power performance was enhanced, and the Pmi value was increased by 30%. The combustion stability was enhanced, and the cycle variation rate of the Pmi was reduced to 16.9%. Nitromethane has a significant effect on improving the combustion characteristics of methanol, and the enhancement of the latter was mainly reflected in the ignition phase of the combustion process. This study indicates that exploring the fuel additive that can increase the concentration of OH radical in the reaction is an effective method to improve the micro-space combustion, which will facilitate the development of micro-piston internal combustion engine to supply energy to a micro electro mechanical system.
Highlights
Micro-energy power systems can achieve ultra-high energy density power output at the micro/intermediate scale by utilizing the energy of chemical combustion reaction to meet the wide needs of micro-aircraft, portable equipment, and other fields [1]
From the perspectives of energy density and conversion efficiency, micro-energy power systems with the liquid hydrocarbon fuel have the potential to compete with the lithium sulfur dioxide (LiSO2) battery system [2]
In order to test the effect of nitromethane and hydrogen peroxide on the combustion characteristics of a micro piston internal combustion engine of methanol with the glow ignition of platinum wire, two kinds of mixed fuels of methanol/nitromethane and methanol/hydrogen peroxide were prepared for combustion diagnosis, respectively
Summary
Micro-energy power systems can achieve ultra-high energy density power output at the micro/intermediate scale by utilizing the energy of chemical combustion reaction to meet the wide needs of micro-aircraft, portable equipment, and other fields [1]. A micro-reciprocating piston internal combustion engine with liquid hydrocarbon fuel has the possibility to supply ultrahigh density energy to a micro electro mechanical system for long-distance transmission. How to achieve stable and efficient transient combustion in micro-space becomes a key challenge that must be solved in the development of a micro reciprocating piston internal combustion engine energy system to supply energy to micro electro mechanical systems. It is proposed and tested to add Micromachines 2020, 11, 96 nitromethane and hydrogen peroxide to promote methanol combustion to improve combustion performance of a methanol micro-piston internal combustion engine This method is convenient and there is no need for additional equipment compared to surface catalytic combustion. The study is helpful to the development of the ultra-high energy density power system of the micro piston internal combustion engine
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