SOME QUESTIONS ON REDUCING THE TOXICITY OF EXHAUST GASES AND SWITCHING TO MULTI-FUEL CAPACITY THROUGH A CONTROLLED COMPRESSION PROCESS IN INTERNAL
НЕКОТОРЫЕ ВОПРОСЫ ПО СНИЖЕНИЮ ТОКСИЧНОСТИ ОТРАБОТАВШИХ ГАЗОВ И ПЕРЕХОДУ НА МНОГОТОПЛИВНОСТЬ ПУТЕМ РЕГУЛИРУЕМОГО ПРОЦЕССА СЖАТИЯ В ДВИГАТЕЛЯХ ВНУТРЕННЕГО СГОРАНИЯ
Naumov A.V., Khusnutdinov A.M., Vasin V.S.
(Southern Ural State University, Chelyabinsk, Russia)
Наумов А.В., Хуснутдинов А.М., Васин В.С.
(ФГАОУ ВО «Южно-Уральский государственный университет (национальный исследовательский университет)» г. Челябинск, РФ)
The article discusses some issues related to reducing the toxicity of exhaust gases and switching to multi-fuel capacity by means of a controlled compression process in internal combustion engines. Theoretical and constructive directions of work on improving the working process of the internal combustion engine are described.
В статье рассматриваются некоторые вопросы по снижению токсичности отработавших газов и переходу на многотопливность путем регулируемого процесса сжатия в двигателях внутреннего сгорания. Описываются теоретические и конструктивные направления в работе по совершенствованию рабочего процесса двигателя внутреннего сгорания.
The key words: compression process, internal combustion engine, multi-fuel capacity, exhaust gases
Ключевые слова: процесс сжатия, двигатель внутреннего сгорания, многотопливность, отработавшие газы
For engines with compression ignition, the main toxic components of exhaust gases are nitrogen oxides, soot, carbon monoxide, and unburned hydrocarbons.
The rate of formation of NOх. almost directly proportional to the increase in the ignition delay period. At the same time, the temperature of the cycle has a decisive influence on the formation of NOх. The formation of carbon monoxide occurs during the period of diffusion burnout and is determined primarily by the lack of oxygen. To reduce CO emissions, it is necessary to intensify the diffusion of oxygen into the combustion zone in the final combustion phase. Reducing the CH content can be achieved by reducing the ignition delay period, which is directly affected by the parameters of the air charge at the start of fuel delivery .
Due to the increased level of supercharging of diesel engines and the need to implement measures aimed at reducing the Pz, there is an increased interest in pre-chamber mixing, including the use of accumulating cavities and devices for controlling the compression ratio. Reducing the compression ratio in the internal combustion engine leads to a decrease in the concentration of nitrogen oxides in the exhaust gases . The influence of such factors as the ratio of the surface area of the combustion chamber to its volume, the shape of the combustion chamber, the mixture, the advance angle of fuel supply should be considered for reducing the toxicity of the engines.
The organization of the mixture formation and combustion process has a significant impact on the composition of toxic substances in the exhaust gases, and the use of a controlled compression process in the internal combustion engine can be used to reduce the toxicity of exhaust gases . In this case, the selected control method must be combined with the intensification of the working process of each specific engine.
Engines with an adjustable compression process can be easily adapted to use on different types of fuels, since they can change the temperature and pressure at the end of compression, and, consequently, affect the period of ignition delay .
In addition to satisfactory power and efficiency, these engines have acceptable dynamics of the operating cycle over the entire range of loading modes when working on several types of fuels, for example, diesel, gasoline, any mixture of them, kerosene, gaseous and liquid fuels.
In comparison with liquid fuel, gas has a higher octane number (85–125). Especially high anti-knock properties of methane, which is the main component of natural associated petroleum gases. An exception among gaseous fuels is hydrogen, which has a low octane number (70) and requires special conditions if it is used as a motor fuel. When hydrogen is burned, a non- toxic source product is formed-water.
Conventional internal combustion engines do not require large structural changes when converting to hydrogen fuel. The key problem of using hydrogen as a fuel for internal combustion engines, especially transport vehicles, is its storage .
One of the most effective ways to increase the power and efficiency of carburetor engines when converting them from liquid to gaseous fuel is to increase the compression ratio. For gas engines, the upper limit of the compression ratio determined by detonation is higher and can reach 10–13 instead of 8–9 for engines running on liquid fuel. With an increase in the compression ratio at a constant exhaust gas temperature, the engine power increases by 20%; with a constant power, the efficiency increases by 15–20% and with a constant composition of the working mixture, the power increases by 25%, and the efficiency increases by 15–20% .
On engines that do not have special devices for changing the compression ratio, it is usually increased in two ways: by installing a new cylinder head with a smaller volume of the compression chamber or new pistons with an elongated upper part.
When converting to a gas-liquid process for different types of diesels, the compression ratio is selected so that there is an inequality between the temperatures: TJ<TS<TGV (where TJ – is the self-ignition temperature of the air-liquid fuel mixture; TGV – is the self-ignition temperature of the gas-air mixture).
For diesels running on gas with a liquid fuel additive, the maximum allowable compression ratio depends on the method of mixture formation. With jet and vortex mixing, it is practically possible to work on gas at a compression ratio of 16-20 (depending on the speed and size of the engine).
The 4Ч 42.5/60, 4Ч 26/38 and БК43 BK43 engines were successfully tested in the gas-liquid cycle without changing the compression ratio (ɛ = 13) .
When converting from liquid fuel to gas, an interchangeable pre − chamber with a volume of 20-35% of the combustion volume is installed instead of a diesel nozzle, which reduces the compression ratio to a level that ensures the non-detonation combustion of the gaseous fuel. Along with reducing the compression ratio, the diesel engine uses a main fuel-gas supply system and an Autonomous pre-chamber gas supply system.
It should be borne in mind that gas engines with electric ignition of the mixture have ɳi = 0,26...0,30 and ɳc = 0,21...0,26; and for gas-liquid engines, which currently have an average flow rate of 15−20% of the amount of fuel supplied by the pump when the engine is running only on liquid fuel, due to a higher compression ratio, it is characteristic ɳi = 0,36...0,45 and ɳc = 0,29...0,36.
Previously, it was experimentally proved that gas-liquid engines, although dual-fuel, are more economical and allow switching from liquid fuel to gaseous fuel and back at any time, including at full load .
The adaptation of engines to work on fuels of different fractional composition is an actual direction of improving the internal combustion engine. When using high-octane fuels in diesels instead of diesel fuel, their Flammability and, consequently, the dynamics of the cycle deteriorate, which causes an increase in mechanical tension and wear of engine parts. At the same time, efficiency is reduced and engine power is reduced.
To ensure multi-fuel capacity, a number of methods are used: variable compression ratio; changing the air temperature at the inlet, recirculation of exhaust gases; controlled injection and new principles for organizing the working process.
Recirculation is usually, used in idle and low load modes when the temperatures are too high α.
To fully solve the problem of multi-fuel capacity in engines, it is necessary to use a complex set of measures to prepare air for the moment of ignition and use a controlled system for preparing fuel and feeding it to the combustion chamber.
Multi-fuel engines of the French company Hispano-Suiza are equipped with a separate vortex chamber of automatically adjustable volume [6, 7]. They are adapted to work on diesel fuel, kerosene and gasoline. Continental (USA)  when developing an engine with different fuels, we investigated a large number of combustion chamber variants in order to achieve satisfactory dynamics and efficiency of operating cycles.
When converting diesel to various light fuels, there is a problem of the dynamics of the combustion process and reducing the ignition delay period.
Therefore, to use gasoline with an octane number greater than 90, ɛ = 22...25 is required. This compression ratio must be the initial highest compression ratio of a multi-fuel engine .
The flammability conditions of the various types of fuel used, as well as the method of mixing and parameters of the fuel injection equipment determine the range of changes in the compression ratio.
Engines with an adjustable compression process can be converted to work with different types of fuel. However, certain experimental finishing works are required, for example, the choice of the optimal injection advance angle for the fuel grade and measures to ensure the start of the diesel engine at low temperatures, which, in turn, can be solved by :
1) changes in the design of the internal combustion engine (optimization of the algorithm for controlling the fuel equipment in the start-up modes, increasing the power of the starter, etc.), this direction can also include the use of low-viscosity (thickened) oils;
2) the use of special technical means, which are usually divided into two groups:
- prestart preparation tools - systems that ensure the creation of favorable conditions for starting before the start of engine scrolling;
- means of facilitating start-up - systems that ensure the creation of favorable conditions for starting after the start of the engine, can include special starting fluids with a low self-ignition temperature, which are injected into the combustion chamber at the time of start-up.
The list of the used sources
1. Zvonov V.A. Toksichnost' dvigatelej vnutrennego sgoraniya. M.: Mashinostroenie, 1981. 160 s.
2. Huciev A.I. Dvigateli vnutrennego sgoraniya s reguliruemym processom szhatiya. M.: Mashinostroenie, 1986. 104 s.: il.
3. Bruk M.A., Viksman A.S., Levin G.H. Rabota dizelya v nestandartnyh usloviyah. L.: Mashinostroenie, 1981. 207 s.
4. Dizeli: Spravochnik. Pod redakciej V.A. Vanshejdt i dr. L.: Mashinostroenie, 1978, 137 s.
5. L.K. Kollerov, M.E. Nizhnik i dr. Energeticheskie ustanovki s gazovymi porshnevymi dvigatelyami. L.: Mashinostroenie, 1979. 245 s.
6. Kotel'nikov V.I. "Vos'merki" "Ispano-Syuizy" v Rossii // Nauchno-tekhnicheskij zhurnal «Dvigatel'» №1 (67) 2010 g. (http://engine.aviaport.ru/issues/67/page30.html).
7. Kotel'nikov V.I. Sovershenstvovanie motorov "Ispano-Syuiza" 12Y Vladimirom YAkovlevichem Klimovym // Nauchno-tekhnicheskij zhurnal «Dvigatel'» №3 (39) 205 g. (http://engine.aviaport.ru/issues/39/page42.html).
8. International global operation «Continental Aerospace Technologies™» (https://www.continentalmotors.aero/company/about-us.aspx).
9. Naumov A.V., Malozyomov A.A. (i dr.) Nekotorye napravleniya sovershenstvovaniya puskovyh kachestv pervichnogo dizelya v sostave mnogofunkcional'nyh energotekhnologicheskih kompleksov // Novye materialy i tekhnologii v mashinostroenii. 2019. №29. P.122-125.