Theory and practice of diagnostics of fire hazardous modes of operation of catalytic converters

Introduction. The wide-scale use of catalytic converters and particulate filters in automobile engines has aggravated the problem of their ignition and updated the research and methodological framework for the examination of causes of fire emergency modes (FEMs) of operation of fuel catalytic units (FCUs). The relationship between the FEMs of the FCU operation and failures of the fuel equipment, wear of the cylinder-piston group of engines and deviations in fuel compositions was confirmed. The goal was to develop a diagnostic method for fire hazardous modes of operation of FCUs of vehicles. Methodology. A model of oxidative catalysis underway in the FCU has been proven rational. The model is used to calculate the thermo-catalytic efficiency and heat generation in the active layer of the γ-Al2O3 platinum catalyst depending on the temperature of exhaust gases (EG), concentrations of CO, CH and soot. It has been found out that catalysis can theoretically develop in four limit domains: internal kinetic domain, internal diffusion domain, external diffusion domain, and external kinetic domain. Results and discussion. Experimental and computational studies have shown the probability of emergence of breakdown vehicles with a multiple excess of soot emissions and thermal stresses. A 10‑fold increase in CO, CH and soot in EG rises the thermal performance of the catalytic reaction from 17,282 to 491,907 kJ/h, creating a fire hazard in a KamAZ engine. To identify a FEM, the diagnostic method based on the «free acceleration» (FA) mode according to GOST 33997–2016 is proposed. The procedure is supplemented with maximum revolutions and restrictions (0.5 s) of the FA mode time. The latter is necessary for the guaranteed operation of the engine in the «full load mode». The method was applied in the course of the fire engineering studies on a Ford Mondeo car having a TDCi (Common Rail System) diesel engine and a catalytic particulate filter. Laboratory examination and analytical studies have found that the main reason for the operation of FCU in emergency (due to environmental and fire hazards) modes is the corrosion of precision parts of the fuel equipment accumulated during its long-term operation. Progressive corrosion is caused by excessive sulfur and moisture content in fuel and oil. Conclusions. It's been proven that the emergency heating of a catalytic converter causes a sharp rise in the car combustion risk. The authors have proposed an original method for the diagnostics of fire-hazardous modes of operation of catalytic converters based on procedures set in GOST 33997–2016 (ТР ТС 018/2011).