Abstract
Deep choke modes that include the no-load conditions are the most long lasting while operating a car in the city environment. However, the efficiency of work process at the deep choke modes remain low due to high intake depression and the large proportion of residual gases. The paper covers the evaluation of the hydrogen influence on the irregularity of compressed natural gas (CNG) combustion behavior in the engine at the no-load conditions through the assessment of change of the polytropic index as the parameter displaying the direction and the intensity of heat-exchange processes. The paper considers the feasibility to determine the quantity of residual gases and their proportion in working mixture. Carried out experimental study of the hydrogen influence on the cycles irregularity at the idle modes of the VAZ-2111 engine showed the decrease of variation of maximum pressure in the engine cylinder when increasing the proportion of hydrogen in gas fuel from 0 up to 6 %. The authors carried out the detailed study of hydrogen influence on the cycles’ irregularity for three stoichiometric ratios of the CNG mixture with the hydrogen proportion of 0, 4 and 6 %, three the most representative successive cycles displaying the irregularity of engine operation were selected for each of them. The study of the polytropic index on the selected cycles allowed determining the quantity of the residual gases and their proportion in working mixture and showed the significant influence of quality of combustion in the previous cycle on the thermodynamic processes behavior within the compression stroke and the combustion process efficiency in the next cycle. The obtained results allow evaluating the influence of hydrogen addition on the CNG combustion process and concluding that the addition of 6 % hydrogen allows better initiating the ignition process, thereby, preventing the ignition failures and decreases significantly the number of incomplete combustion cycles increasing the efficiency of working process at the idle modes.
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