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The influence of the turbulent speed of flame propagation on the indicated characteristics of the aircraft piston engine is investigated. It was revealed that an increase of the flame speed contributes to a decrease of fuel consumption, an increase of efficiency and power of the engine.

The results of an experimental study of the relationship between the width of the turbulent combustion zone (TCZ) and the composition of the composite fuel (hythane), the maximum pressure in the combustion chamber of variable volume, and the propagation speed and electrical conductivity of the turbulent flame are presented. It was found that the width of the TCZ has a characteristic dependence on the composition of hythane. It was experimentally found that, despite the change in the coefficient of excess of air, the hydrogen concentration in the fuel, the turbulence intensity and type of fuel (hythane and gasoline), and the dependences of the TCZ width on the turbulent flame propagation velocity and on the electrical conductivity of the flame remain unchanged, as well as the dependence of the maximum pressure on the width of the TCZ. The results of the work can be used in the design and development of energy-efficient and low-emission combustion chambers.

The paper considers the turbulence intensity and the fuel chemical composition impact on the flame propagation velocity at the initial and main combustion phases when changing the air-fuel mixture composition. The relevance of the study is caused by the fact that currently, the improvement of conventional engine operation characteristics is mainly achieved through the improvement of the fuel mixture combustion process. However, there are no data on the influence of chemical and gas-dynamic factors on the peculiarities of flame propagation at the initial and main combustion phases. The gas reciprocating internal combustion engine was the object of the research, and the subject of the study was the fuel combustion process. Fuel chemical composition changed due to the promoting addition of hydrogen to the natural gas and variations of the excess-air coefficient. The experiments carried out on the UIT-85 power plant (i.e. under the simulated internal combustion engine conditions) show that the promoting addition of hydrogen stronger influences the flame velocity in the initial combustion phase compared to the second combustion phase, as a combustion source in the first phase is a laminar flame bent front and depends only on chemical and thermo-physical properties of the fuel-air mixture. The analysis of experimental data showed the dual impact of turbulence intensity on the flame propagation velocity. In particular, at the beginning of the combustion process, the fluctuating velocity scarcely influences the flame propagation velocity, as opposed to the main combustion phase, where the flame propagation velocity increases at the increase of turbulence intensity.

The investigation considers how combustion efficiency and exhaust gas (unburnt hydrocarbon) toxicity are linked to the fundamental flame propagation characteristics (flame propagation velocity and reaction zone width). We present combustion efficiency and unburnt hydrocarbon concentration as functions of fundamental flame propagation characteristics, maximum flame temperature, flame failure temperature and thickness of the unburnt fuel layer adjacent to the combustion chamber walls. Comparing combustion efficiency computed according to the equation proposed to combustion efficiency derived by using an experimentally obtained indicator diagram showed that the data are in good agreement. We studied the connection between unburnt hydrocarbon emission and combustion efficiency. We detected that increasing combustion efficiency leads to lower unburnt hydrocarbon emission, which is explained by reduction of the unburnt fuel ratio in the layer adjacent to the wall. We propose a new technique for calculating unburnt hydrocarbon amount in engine exhaust gases. We show that our technique makes it possible to determine the chemical composition of the air-fuel mixture and the values of flame propagation characteristics that ensure a decrease in unburnt hydrocarbon emission. The results of our study may be used to develop or refine methods of increasing combustion efficiency of composite fuels and reducing exhaust gas toxicity in combustion chambers of internal combustion engines and other power plants.

The article analyzes the influence of chemical composition of hythane (a mixture of natural gas with hydrogen) on pressure in an engine combustion chamber. A review of the literature has showed the relevance of using hythane in transport energy industry, and also revealed a number of scientific papers devoted to studying the effect of hythane on environmental and traction-dynamic characteristics of the engine. We have studied a single-cylinder spark-ignited internal combustion engine. In the experiments, the varying factors are: engine speed (600 and 900 min-1), excess air ratio and hydrogen concentration in natural gas which are 29, 47 and 58% (volume).The article shows that at idling engine speed maximum pressure in combustion chamber depends on excess air ratio and proportion hydrogen in the air-fuel mixture – the poorer air-fuel mixture and greater addition of hydrogen is, the more intense pressure increases. The positive effect of hydrogen on pressure is explained by the fact that addition of hydrogen contributes to increase in heat of combustion fuel and rate propagation of the flame. As a result, during combustion, more heat is released, and the fuel itself burns in a smaller volume. Thus, the addition of hydrogen can ensure stable combustion of a lean air-fuel mixture without loss of engine power. Moreover, the article shows that, despite the change in engine speed, addition of hydrogen, excess air ratio, type of fuel (natural gas and gasoline), there is a power-law dependence of the maximum pressure in engine cylinder on combustion chamber volume. Processing and analysis of the results of the foreign and domestic researchers have showed that patterns we discovered are applicable to engines of different designs, operating at different speeds and using different hydrocarbon fuels. The results research presented allow us to reduce the time and material costs when creating new power plants using hythane and meeting modern requirements for power, economy and toxicity.

The prospects using methane-hydrogen fuel in power plants are shown. The effect of turbulence intensity on propagation velocity and width of the zone of chemical reactions methane-hydrogen flame in combustion chamber of variable volume is investigated. The article shows that effect of turbulence intensity on propagation velocity and flame width depends on fuel excess coefficient. During combustion of stoichiometric fuel-air mixtures, an increase in turbulence leads to a more noticeable increase in flame velocity than when burning poor and rich mixtures. It was experimentally found that increase in intensity of turbulence leads to a noticeable change in width of the flame only when burning poor and rich fuel-air mixtures. Processing of the results of foreign and domestic scientists has shown validity of our laws for combustion chambers of different designs using different hydrocarbon fuels. The results of the work can be used in design and debugging of energy-efficient and low-emission combustion chambers.

The article investigated the effect of excess air coefficient α, the concentration of the combustion activator (hydrogen) in the fuel, the phases of combustion, and the location of ionization sensors in the combustion chamber on the duration of the ion current signal. It was found that the excess air coefficient affects the duration of the ion current signal in the first and second phase of combustion. For α 1.1, the duration of the ion current signal increases. It was experimentally found that the activation of combustion due to the addition of hydrogen leads to a decrease in the duration of the ion current signal. This is due to an increase in the rate of chemical reactions in the flame front. Analysis of analytical and graphical dependences showed that taking into account the duration of the ion current signal in the first phase of combustion allows us to predict the duration of the ion current signal in the second phase of combustion. The results work will find a wide application in the creation of control systems and diagnostics of the combustion process in power plants using ionization sensors.

The results of a study of the influence of turbulent flame propagation velocity and the width of the zone of chemical reactions of the flame in the second phase of combustion on the indicator characteristics of the engine (power, specific fuel consumption, and efficiency) are presented. The object of the study was a single-cylinder, four-stroke piston internal combustion engine with spark ignition. When analyzing the research results, analytical and graphical dependencies of the indicator characteristics of the engine on the turbulent flame speed and flame thickness are obtained. It was found that the indicator power of the engine increases linearly with increasing flame speed and decreasing flame thickness in the second phase of combustion. Experiments have shown that with an increase the flame speed from 12.5 to 17.4 m/s and a decrease the flame thickness from 23 to 17 mm, the indicator power increased by 29%. This is because with these characteristics of flame propagation, an increase pressure in the combustion chamber of the engine from 1.9 to 3.7 MPa. As a result, the average indicator pressure, the indicator operation of the cycle and, therefore, the indicator power increase. It is shown that in order to reduce indicator specific fuel consumption by 10% and increase indicator engine efficiency by 10%, it is necessary to intensify the combustion process of poor fuel-air mixture (α>1.3), i.e. increase turbulent flame speed by 38% and decrease flame thickness by 26%. Since the intensification of the combustion process of poor mixtures leads to an increase in heat release, average indicator pressure and completeness of fuel combustion.

In the present paper, we have experimentally studied the dependences of the maximum temperature of the hydrocarbon flame on the electron current (due to the flame chemi-ionization), the width of the turbulent combustion zone, and the amount and composition of the air-fuel mixture in the combustion chamber of variable volume. Based on the proposed formula, we have been also able to estimate the temperature and compare with its experimental value showing that the convergence has been more than 85% at an excess air factor value ranging from 0.8 to 1.15. The obtained results can be used to predict and monitor the maximum flame temperature in the combustion chamber of an internal combustion engine and other power plants by using the ionization probe.

The article presents the designs of ionization sensors, intended for the determining of the characteristics of flame propagation. The values of the ion current, the turbulent velocity of flame propagation and the width of the zone of chemical combustion reactions are determined, depending on the composition of the fuel-air mixture when its physico-chemical properties change due to the addition of hydrogen. It is shown that the change in the turbulent flame velocity is due to an increase in the normal flame velocity. It is revealed that the flame width is linearly related to the ion current and reflects the intensity of the chemical combustion reactions. The examples of the use of electrical conductivity characteristics for determining the flame temperature and the concentration of unburned hydrocarbons in the exhaust gases are given.

An indirect method of estimating the visible flame propagation speed of the methane–hydrogen–air mixture with account of carbon content in the fuel mixture and the ion current amplitude is proposed by the experimental results. By comparing the calculated and experimental values, it has been shown that an approach using the methane–hydrogen mixture is advisable at the stage of the internal combustion engine design and development.

The results of an experimental study of the relationship between the propagation velocity of a methane-hydrogen flame and the maximum pressure in the combustion chamber of variable volume and pulsating velocity are presented. The article shows that the influence of the pulsation velocity on the flame propagation velocity depends on the phase of combustion, i.e. the larger the size of the combustion zone, the stronger the influence of the pulsation velocity and the coefficient of excess fuel. When stoichiometric mixtures are burned, an increase in the pulsation velocity leads to a more noticeable increase in the flame velocity than when burning poor and rich mixtures. It was experimentally found that, despite the change in the coefficient of excess air, the concentration of hydrogen in the fuel and the pulsating velocity, a direct linear dependence of the maximum pressure in the combustion chamber on the flame propagation rate is maintained. Processing the results of foreign scientists showed the validity of the laws we obtained for combustion chambers of various designs. The results of the work can be used in the design and development of energy-efficient and low-emission combustion chambers of variable volume.

The article is dedicated to experimental and theoretical studies characteristics flame propagation in combustion chamber internal combustion engine with spark ignition and their influence on completeness combustion. It is theoretically and experimentally proved that relationship of flame propagation characteristics with completeness of combustion composite fuel is complex, non-linear, and depends on chemical composition combustible mixture and temperature in combustion chamber. It was revealed that an increase thickness near-wall unburned fuel layer, size of slots in combustion chamber and surface area of combustion chamber contribute to a reduction combustion efficiency of the fuel. It is shown that an increase rate flame propagation and a decrease thickness flame front leads to an increase completeness combustion fuel. It was revealed that proposed formula, using fundamental characteristics of flame propagation, allows to us calculating completeness combustion composite fuel. This indicates feasibility using this formula at the design stage and fine-tuning low-emission and energy-efficient combustion chambers of engines and power plants.

The article is dedicated to experimental and theoretical studies characteristics of flame propagation in combustion chamber of internal combustion engine with spark ignition and their influence on completeness combustion. It is theoretically and experimentally proved that relationship of flame propagation characteristics with completeness of combustion composite fuel is complex, non-linear, and depends on chemical composition combustible mixture and temperature in combustion chamber. It was revealed that an increase thickness near-wall unburned fuel layer, size of slots in combustion chamber and surface area of combustion chamber contribute to a reduction combustion efficiency of the fuel. It is shown that an increase rate flame propagation and a decrease thickness flame front leads to an increase completeness combustion fuel. It was revealed that proposed formula, using fundamental characteristics of flame propagation, allows calculating completeness combustion composite fuel. This indicates feasibility of using this formula at the design stage and fine-tuning low-emission and energy-efficient combustion chambers of engines and power plants.

We have considered the functional dependence of the ionization detector readings (ion current) on the composition of the fuel–air mixture, adiabatic temperature, and the turbulent combustion zone width. Experiments on the engine show that, for an air excess factor of 0.75–1.15, the coincidence of the calculated and experimental data exceeds 90%. Our results can be used to predict and monitor the adiabatic temperature of the flame and the width of the turbulent combustion zone in the combustion changer of the internal combustion engine using the ionization detector.

The article experimentally proves the interconnection of ion current with a carbon concentration in fuel and apparent propagation velocity of the flame. This confirms the hypothesis about the strong influence of rate of radical CH + formation on ion current and allows the use of its amplitude to determine characteristics of flame propagation, which greatly simplifies and reduces the cost of existing research methods using ionization probes of combustion process in piston engines.