PRESUMPTIONS OF EFFECTIVE OPERATION OF DIESEL ENGINES RUNNING ON RME BIODIESEL. RESEARCH ON KINETICS OF COMBUSTION OF RME BIODIESEL

. The results of experimental research on kinetics of fuel combustion of diesel engine A41are presented in the publication. The change of characteristics of indicated work (in-cylinder pressure and temperature, period of induction, heat release and heat release rate) and fuel injection (fuel injection pressure, fuel injection phases) was determined in diesel engine running on RME biodiesel being compared to diesel fuel. The results of researches were used to explain experimentally determined changes of operational and ecological characteristics of diesel engine running on RME biodiesel. In addition, the reliability of diesel engine A41 running on RME biodiesel was evaluated. The pre-sumptions of effective operation of diesel engines running on RME biodiesel were formulated.

Publication continues the presentation of results of common researches of Lithuanian Agricultural University and Klaipėda University into production and adaptation of biodiesel in fleets of diesel engines of Lithuania. Researches are conducted under the auspices of Council of science and studies of Lithuania and performed under the framework of international project "EUREKA. BIOWASTEFUEL.E!3234". The results of researches on chemical, physical and motor properties of various biodiesels, as well as on the change of operational and ecological characteristics of diesel engine running on biodiesel were presented in previous publications. The results of research on kinetics of combustion and fuel injection of diesel engine A41 are presented in this publication. The presumptions of effective operation of diesel engines running on RME biodiesel are formulated on the basis of the obtained results of researches. Experimental researches were performed together with Altaj State Technical University (Russian Federation).
Nowadays the researches on biodiesel fuel are directed to reduction of cost price [1] and improvement of low temperature characteristics. The usage of waste vegetable oils and animal fats for the production of biodiesel is one of the promising ways to reduce the cost price of biodiesel. The improvement of low temperature characteristics is solved by applying fuel additives. As a result, the multicomponental biodiesel fuels are created. The base of new types of biodiesels consists of traditional types of biodiesel: rapeseed methyl ester -RME, soybean methyl ester -SME, palm-oil methyl ester -PME. The new biocomponents change properties of biodiesel and influence differently the work process of diesel engine which forms the main technical-economical and ecological parameters. The comparative research on characteristics of indicated work of diesel engine forms the base to choose the proportions of biocomponents of new biodiesels, which practically realises the engineering of fuel. It also allows to evaluate the optimum and critical values of parameters of biodiesel and to take compromise decisions regarding optimisation of regulation parameters of diesel engine.
The goal of the performed research was to evaluate the change of parameters of fuel injection and kinetics of fuel combustion of diesel engine A41 running on RME biodiesel. The results of research will be used to prove the observed changes of operational and ecological parameters, to evaluate the change of reliability of diesel engine and formulate the presumptions of effective operation of diesel engines running on RME biodiesel.

Materials and methods
The object of the research is chosen in respect of the structure of diesel engines park of Agricultural machines of Lithuania (see Fig 1) and technical characteristics of mostly spread models of diesel engines.
Such choice enssures the possibility of practical application of obtained results of the research. The object of the research is the section of one cylinder of tractor purpose diesel engine A41 (producer JSC "Altaiskij motornij zavod", Russian Federation).
The main physical-chemical and motor parameters of tested fuels are presented in Table 2. The parameters of high pressure fuel injection system and indicated process were measured by piezo sensors. The in-cyliner pressure P g , fuel injection pressure P f , the start of fuel injection phase φ f1 and the end φ f2 were measured. The error of measurement of pressures P g and P f is ± 0,5 %. The error of measurement of fuel injection phases (φ f1 and φ f2 ) and characteristic angles of cranckshaft is ± 0,5 ºCA. The signals of sensors were transferred by 20 channels into registration station of high-speed processes H-2000. The received signals were treated and collected by program complex "AC-Test". The mathematical modelling of temperature of gases and characteristics of heat release were performed by applying the program complex "Cycle". The main aspects of research on indicated process and fuel injection process are shown in Fig 2.   Fig 2.The aspects of research on work process and characteristics of fuel injection of diesel engine A41 The properties of heat release have influence on power, fuel consumption, reliability, the level of sound, vibration and harmful emission of exhaust gases of diesel engine. The process of formation of fuel -air mixture has primary influence on heat release. This process depends on dynamic state of air charge and fuel injection properties. Because of that the research on kinetics of combustion is related with research on characteristics of fuel injection.
XK and XA types of thermocouple are used for measurement of the temperature of cooling liquid, lubricating oil and exhaust gases of diesel engine. The relative error of measurement of temperature is ± 1 %. Fuel consumption is measured with automated device AБP-50. The relative error of measurement of fuel consumption is ± 0,5 %.
The algorithm for calculation of characteristics of heat release X = f(φ) and dX/dφ = f(φ) is based on differencial equation of first law of thermodynamics: where p and T -in-cylinder pressure and temperature; ' G and " G -masses of air and products of complete combustion; ' v c ir " v c -isochoric specific heat capacity of air and products of complete combustion; q cycle -the portion of fuel injected during one cycle; Q w -heat losses through cylinder liner into cooling system, which can be alternatively calculated by methodics of G. Woschni [2] or Central Institute of Diesel Reseach (St. Peterburg, Russian Federation) [3]; X -coefficient of heat release; K 4 -constant; P B -trigonometric function.
The possibility to enter the chemical composition of a wide range of fuels is realised by the mathematical model. The following chemical elements can be entered: coal -C, hydrogen -H 2 , oxygen -O 2 , water -H 2 O, sulphur -S. The chemical composition of fuel oxidator (air) is entered by the following components: O 2 , nitrogen -N 2 , carbon dioxide -CO 2 , H 2 O and argon A r . The values of internal energy and specific heat capacity of air and products of complete combustion are calculated by empyrical extrapolational polynomial equation of the third degree [4]: where A 0 , A 1 , A 2 , A 3 -coefficients, which are calculated by third degree polynomial equations depending on temperature and mass values of air and products of complete combustion (N 2 , CO 2 , H 2 O, SO 2 and A r ). Stoichiometric ratio L 0 of the ammount of air which is theoretically required for complete combustion of fuel, is calculated depending on chemical composition of fuel by formula: -mass portions of fuel elements, kg/kg fuel.
The heating value H U is determined by formula of Mendelejev widely used in practice: -mass portions of fuel elements, kg/kg fuel.
The thermal and mechanical load of parts of cylinder -liner group can be evaluated by widely used in practice indirect criterions, which is allowable in comparative research. The following indirect criterions were used: • maximum in-cylinder pressure p max : for evaluation of mechanical load; • maximum in-cylinder temperature T max and medium temperature of compression -power stroke T cycle : for evaluation of thermal load; • criterions of prof. A. Kostin q p ir q y : for evaluation of the thermal load.

The results of experimental researches
The air ratio α is one of the main parameters which influences the work process of diesel engines especially without air turbocharging. The air ratio α is calculated by formula: , where G air -air consumption per hour, kg/h, G f -fuel consumption per hour, kg/h. The air ratio of biodiesel increases depending on lower value of stoichiometric ratio: 0,476 and 0,433values of biodiesels B30 and B100 compared to value of mineral diesel fuel -0,495. The consumption of air G air is consistent under equal environmental conditions and equal work regimes. In this case the air ratio depends only on fuel consumption G f and stoichiometric ratio L 0 . The fuel consumption can be expressed by formula: , where b e -brake specific fuel consumption, g/kWh, P e -diesel engine brake power, kW. The air ratio becomes the function of two arguments: b e and L 0 at the identical diesel brake power (P e = const). The biggest change of brake specific fuel consumption is determined at low loads of diesel engine running on biodiesel (see Fig 3). The higher value of air ratio of biodiesel is predetermined by different values of stoichiometric value L 0 being compared with mineral diesel fuel at low loads. This difference compensates the growth of break specific fuel consumption b e by increasing workload. The increase in air ratio α is the following for the biodiesels being compared with mineral diesel fuel: B30 ~ 0,5 ÷ 0,15 and B100 ~ 0,75 ÷ 0,3, α ≈ idem at nominal loads. The effectiveness of convertation of the heat of fuel combustion into indicated work is evaluated by overall efficiency factor η i . It can be determined as a function of the following parameters: air ratio α , compression ratio ε and ratio p max /p a (p a -pressure of working fluid at the beginning of compression stroke) [5]. ). The pressure ratio λ depends mainly on cycle quantity of fuel q cycle or fuel consumption per hour G f by constant regulation of fuel supply systems for diesels without turbocharging. The linear dependence, viz. pressure ratio λ change can be seen depending on load of diesel engine (see Fig 3). The value of pressure ratio λ differs only by 2 ÷ 3 % for the different tested fuels at constant rated output P e ( ' / ' , where p cpressure of working fluid at the start of combustion, (see Fig 3). In case of made notes the indicated efficiency factor depends exceptionally on air ratio α.  (see Fig 3) [7]. The equivalent fuel consumption experimental determination is less complicated in practice. The observed relative change of equivalent fuel consumption is similar to relative change of indicated efficiency factor when replacing mineral diesel fuel by biodiesel.

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. 2  .  T  h  e  m  e  c  h  a  n  i  c  a  l  a  n  d  t  h  e  r  m  a  l  l  o  a  d  o  f  d  i  e  s  e  l  e  n  g  i  n  e The temperature of exhaust gases T r is a less sensitive parameter than indicated efficiency factor in case of replacing the sort of fuel. Almost identical level of the temperature of exhaust gases T g was determined for the following sorts of fuel: mineral diesel fuel, B30 and B100 at P e = idem (see Table 3). The temperature of exhaust gases T g is widely used in practice as indirect criterion for evaluation of thermal load of parts of cylinder-liner group of diesel engine. The temperature of exhaust gases non-completely reflects thermal load of diesel engine because of changes of spontaneous fuel injection phases at running of diesel engine on different sorts of fuel. The following parameters are used additionally for evaluation of the change of thermal load: maximum in-cylinder temperature T max , medium temperature of compression -power stroke T cycle and criterions of prof. A. Kostin q p and q y (see Fig 5).
Obtained results show that the replacement of mineral diesel fuel with biodiesel up to concentration of B100 does not increase mechanical load of parts of cylinder-liner group of diesel engine. The identical value of maximum pressure p max is obtained independently on the sort of fuel at constant rated output P e = idem. Experimental data curve of maximum pressure divergence from generalized curves is about ± 1 ÷ 1,5 bar (see Fig 3). Criterions q p and q y are proportional to relative flow of heat near the bottom of piston and cooling system of diesel engine: where D -diameter of cylinder, η v -air ratio of filling the cylinder, c m -medium speed of piston, p k -turbocharging pressure, T k -temperature of turbocharging air, T 0 -environmental temperature. After non-complicated simplifying for the diesel without turbocharging the functions of criterions q p and q y can be expressed as follows: -ratio of usage of air fluid, reverse to air ratio α , K 1 and K 2 -constants. The determined change of criterions q p and q y of different sorts of fuel depending on load (see Fig 5) confirms that replacement of mineral diesel fuel by biodiesel does not increase thermal load and heat transferring into cooling system at the same level of rated output.

The characteristics of fuel injection
The replacement of mineral diesel fuel by biodiesel practically does not change the phases of fuel injection (ϕ f1 -start of injection and ϕ f2 -end of injection) and duration of injection at the same fuel injection timing and rated output.
The charcateristic phases of biodiesel injection remain the same being compared with mineral diesel fuel (see Fig 6).
The analogous results of researches are obtained and for rapeseed oil while viscosity of it is ~ 15 % higher being compared to mineral diesel fuel. The viscosity of biodiesel B100 is ~ 85 % and density is ~ 5 % higher being compared to mineral diesel fuel.
The replacement of mineral diesel fuel with biodiesel ensuring the same level of rated output of diesel engine is related to the increase of cycle quantity of fuel q cycle because of lower heat value H u of biodiesel. The constancy of duration of fuel injection inj f ϕ confirms that the intensiveness of injection or pressure of injection (speed of volume and mass injection) increases by using biodiesels. The increase of fuel pressure before fuel injector P f is determined within the whole researched range of loads (see Fig 7). The higher pressure before fuel injection P f of biodiesels stabilizes characteristic of fuel injection. The real timing of lifting of injector needle is earlier for 1 ÷ 1,5 º CA up to dead top center (see Fig 8). − diesel fuel, − RME biodiesel B30, − RME biodiesel B100 The front of characteristic of fuel pressure before fuel injection remains unchanged (see Fig 9). Is it known that the increase of profile and maximum value of P f together with density of fuel significantly influence the quality of fuel injection: the size of fuel droplets, the dispersity and, as a result, period of induction φ i and kinetic phase of combustion. The law of fuel injection in differential and integral ) (x f g = forms can be reasonably estimated depending on experimentally determined characteristic where P cil -in-cylinder pressure, G -cycle portion of fuel, n s -revolutions of fuel pump crankshaft, p p f , μ effective square of holes of injector. Experimentally obtained and manually treated characteristics ) (ϕ = f g at corresponding values of indicated pressure p mi shows that the law of fuel injection remains the same when replacing the mineral diesel fuel by biodiesel. The above data made available to state that the critical deviations of macro factors of fuel injection are not determined for the replacement of mineral diesel fuel by biodiesel up to pure biodiesel B100, and extra regulation of fuel supply system is not required. The torch of biodiesel is characterised by worse micro factors of injection -dispersity of injection because of higher values of density ρ, viscosity . (8) The influence of parameters ρ, υ and σ on diameter D 32 of droplets of torch is estimated by index of degree. It is obvious, D 32 is mostly influenced by viscosity υ and forces of surface tension σ . The force of surface tension σ Bio of biodiesel is higher approximately by 10 %, the value of viscosity of biodiesel is two times higher and thus predetermine the biggest influence on D 32 . The waited overall increase of D 32 is 17 % for biodiesel B100. The characteristics of evaporation of biodiesel is as worse as dispersity: temperature at the start of evaporation of RME -299 ºC, when the same of mineral diesel fuel -178 ºC and higher value of specific enthalpy of evaporation. The influence of working fluid of biodiesel on work process is evaluated by characteristics of heat release X, dX/dϕ = f(ϕ) (see Figs 10, 11). The analysis of characteristics of heat release is accented on the first -kinetic (dX I /dφ) max and the second -diffusion (dX II /dφ) max maximums of speed of heat release.
(dX I /dφ) max forms the dynamic parameters of work process: ratio of pressure speed (dp/dφ) max , pressure ratio λ , maximum pressure of cycle p max and emission of nitric oxides NO x . The character of fuel combustion in the second -diffusion phase influences parameters of fuel economy and emission of products of noncomplete combustion: (carbon monoxide CO, hydrocarbons CH and smoke).
The reduction of induction period φ i for the biodiesel B30 and B100 is determined by 1º CA and 2º CA (see Fig 6). The values of cetane number of biodiesels B30 and B100 are 50 and 57 being compared to the same of mineral diesel fuel -46. The quantity of fuel injected per cycle reduces together with the reduction of induction period φ i , because the start of injection and the law of injection remain constant. The observed reduction of (dX I /dφ) max (see Fig 10) is related to lower quantity of injected and prepared for combustion fuel (because of worse characteristics of evaporation) at the time of induction period. The significant reduction of (dX I /dφ) max is observed at regime of nominal load: (dX I /dφ) max reduces approximately by 30 % from 0,09 °CA -1 down to 0,06 º CA -1 medium indicated pressure p mi = 0,4 ÷0,5 MPa. The change of characteristics of heat release (dX I /dφ) max and (dX II /dφ) max of diesel engine A41 while running on biodiesel: − diesel fuel, − RME biodiesel B30, − RME biodiesel B100 As a result, the dynamic parameters of load reduce: ratio of pressure speed (dp/dφ) max reduces from 0,9 MPa/º CA down to 0,85 MPa/º CA for biodiesle B30 and down to 0,7 MPa/º CA for biodiesle B100 at the regime of load p mi = 0,73 ÷ 0,83 MPa.
The criterions of mechanical load of parts of cylinder-liner group p max and pressure ratio λ depend mainly on heat quantity Q Pmax released until the moment the maximum cycle pressure is reached at the identical conditions. The identical level of Q Pmax ≈ idem is determined for all tested sorts of fuels. The said above confirms the constancy of experimentally determined parmeters p max ,