Abstract
The reduction of pollutant emissions from internal combustion engines, and in particular greenhouse gases, must be achieved by optimizing the combustion process and choosing fuels with a low carbon impact. Heterogeneous mixture combustions such as Diesel induce a difficulty in managing of the pollutants formation even if in its principle the output efficiency remains favorable. Therefore, it is necessary to distinguish this last point, which refers to the compression ratio, in order to move towards homogeneous combustion with a high compression ratio. We then speak generically of HCCI combustion (Homogeneous Charge Compression Ignition), whose process takes place in the context of auto ignition.An important challenge of this combustion is the control of the ignition timing. This paper presents a concept to control the initiation of combustion of a reactive gas mixture with low susceptibility to auto-ignition, which meets the expectation of high efficiency, via the introduction of biomass particles. From a schematic point of view, these particles will play the role of spark plugs distributed throughout the combustion chamber, and should have an auto ignition time much lower than that of the fuel.For this purpose, a particle injector was conceived to directly inject a controlled quantity of biomass powder into the reactive mixture directly. This part is a challenging point. The reproducibility and viability of the particle injector were qualitatively validated by image analysis acquired at high frequency and high resolution. Thus, the system was integrated into an RCM (Rapid Compression Machine) chamber, allowing diphasic gas/solid biomass combustion study. This preliminary test was investigated by high-speed video on a lean diluted biomass enriched with hydrogen mixture (CH4/CO2/H2) at low fuel-air equivalence ratio (Φ = 0.6), with different auto-ignition delays in the condition of experimentation. It was shown that the direct injection of a small amount of biomass particles was able to promote its reactivity and initiate the combustion process. This study highlights the promising effects of the injection of powder to control the beginning of homogeneous combustion, by bringing locally a spot of energy, distributed in the whole chamber. The control given by a global contribution of weak energy is distinguished from the process of combustion by auto-ignition of the fuel mixture whose properties of equivalence air-fuel ratio or dilution will complete the optimization of the process.
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