The improvement in the methods for estimating the nature of the working process of an internal combusting

The urgency of mathematical simulation and electronic processing of obtained experimental data for estimating the working process increases by the day. The solution of real-world problems requires high-speed computer programs that enable us to reliably simulate complex processes occurring in engines and to simplify a considerable part of research effort. In connection with these considerations, the aim of our investigation is the improvement in the methods for estimating the nature of the working process of an internal combustion engine by applying CNIDI techniques for processing indicator diagrams by designing a hardware and software package. The package is able to present the obtained design data of heat-generation law values in a readable form of a digital model that enables us to produce their subsequent export into other software products for further research. The novelty of our work lies in developing a program for personal computers which is able to process experimental indicator diagram obtained in any form and by any technique for acquisition of heat-generation values. The main purposes of our investigation are the analysis of existing CNIDI techniques of processing indicator diagrams, the algorithm design of computer software operation and the verification of data obtained by programmed methods with design data. We found that applying the technique of processing experimental indicator diagrams is one of the methods most reliably describing the processes occurring in diesel cylinders. We analyzed the theoretical basics of a fuel combustion process by using experimental indicator diagrams, examined taking into account imprecision of source data, and validated ways of updating the data. We upgraded the computer program aimed at the methods of heat-generation data calculation under combustion according to specified diagrams. The use of introduced CNIDI techniques and the appropriate program of indicator diagram analysis provide the required quality of results in investigating the influence of various factors on fuel combustion process in an engine.


Introduction
At the present stage of technical development, the design of new combustion engines as well as the improvement of existing ones is impossible without calculated investigations by means of computers. The urgency of mathematical simulation and electronic processing of obtained experimental data for estimating the working process increases by the day. In connection with critical shortage of computer software aimed at the solution of mentioned problems, the major part of research is conducted in the form of experiments. Existing design techniques and implementing these techniques computer programs for simulating processes in combustion engines can be divided into analytic techniques and those obtained by numerical methods. However, these programs do not enable us to completely solve AGRITECH-IV-2020 IOP Conf. Series: Earth and Environmental Science 677 (2021) 052042 IOP Publishing doi: 10.1088/1755-1315/677/5/052042 2 problems of estimating the nature of working process behavior because they lack reliable methods of heat-generation calculation. Available software packages require substantial computational resources. The solution of real-world problems requires high-speed computer programs that enable us to reliably simulate complex processes occurring in engines and to simplify a considerable part of research effort.

Literature review
At the present moment there are a number of techniques for evaluating the nature of working process, i.e. the calculation of heat generation in a combustion engine cylinder. For convenience we can divide these methods into three groups according to the way of obtaining sought data dependency.
Neumann's empirical method [1] represents empirical equation corresponding to the principles of classical kinetics according to which the response rate depends on the concentration of reacting agents. The equation implies that the rate of fuel burnout has peak value in the beginning of combustion process, then it decreases and vanished at the very end. However, the speed of fuel combustion in reciprocating engines occurs according to a chain; consequently, it is not feasible to express the speed of their behavior by equations of classical chemical kinetics.
Gonchar's relation [2] as opposed to Neumann's formula [1] contains exponential function according to which one and the same fraction of cycle feeding burns out upon reaching maximum speed of combustion. Therefore, under the conditions of actual operation of diesels, maximum heat generation has values that are substantially different from maximum showing both a decrease and an increase. The moment of reaching maximum speed of combustion is highly close to the moment of the beginning of burning reaction in modern diesels. In this case the reaction speed has infinitely large value. In real world the maximum combustion speed always has finite value.
Pugachev's relation [3] describes heat-generation speed in a diesel with two maximums as a sum of two heat-generation rates, the approximating function being represented by two summands. The practical application of the relation for calculating pressure change in a combustion chamber is complicated by an increase of driven parameters.
Trigonometric relation [4] allocates heat-generation speed with one maximum, therefore it does not find practical application nowadays and is generally used for estimating the concentration of toxic agents.
Grinevetstsky-Mazing design model [5] implies mathematical idealization of a real-world process occurring in a diesel cylinder. Heat supply (fuel injection) starts when a piston is at its upper dead center; the method does not take into account the advance of the beginning of fuel injection and combustion delay. Considerable discrepancy in experimental and design data is revealed in calculating temperature in the beginning of fuel injection.
Vibe's model [6] is based on a chain mechanism of hydrocarbon fuel combustion; however, heatgeneration law does not reflect physical reality of a process in a combustion chamber in full.
Watson's model uses algebraic equations with empirical coefficients which depend on a mode of engine operation for describing heat-generation speed; the model does not provide calculations accurate enough.
Osten-Lin's model [8] which uses injection speed for calculating heat-generation speed does not take into account kinetic phase of combustion process.
Voshni's method for indictor diagram calculation employs a so-called form factor which represents a relational portion of fuel injected during the autoignition delay period; the method does take into consideration the diffusion phase of combustion process.
Shipinsky's method [10] and Whitehouse-Wai [11] method use regularity of fuel evaporation to describe the combustion process. The disadvantage of the methods may be attributed to impossibility of taking into account influencing factors, such as combustion chamber types, injection parameters, etc. as well as requirement in identification by experimental data, the identification having to be completed prior to performing design investigation.
The method of calculating heat generation in a diesel cylinder based on the obtained experimental indicator diagram by using the first law of thermodynamics was developed in the Central Scientific  [12]. The technique actually reflects the reality of ongoing processes in a diesel cylinder as its foundation lies in data obtained experimentally which makes it indispensable for conducting investigation.

Research objectives
In connection with these considerations, the aim of our investigation is the improvement in the methods for estimating the nature of the working process of an internal combustion engine by applying CNIDI techniques for processing indicator diagrams by designing a hardware and software package. The package is able to present the obtained design data of heat-generation law values in a readable form of a digital model that enables us to produce their subsequent export into other software products for further research. The novelty of our work lies in developing a program for personal computers which is able to process experimental indicator diagram obtained in any form and by any technique for acquisition of heat-generation values. The main purposes of our investigation are the analysis of existing CNIDI techniques of processing indicator diagrams, the algorithm design of computer software operation and the verification of data obtained by programmed methods with design data.

Materials and methods
The object of study is the existing CNIDI's techniques for processing indicator diagrams. An indicator diagram (ID) is known to represent the dependence of pressure in a cylinder on the rotation angle of a crankshaft ( ), thereby it reflects the amount of heat ( ) [13] injected to the working medium.
Let us consider some basics of analysis for indicator diagram. By using the ideal gas law (Clapeyron-Mendeleev equation), the general equation for state of a hypothetical ideal gas, we can determine pressure and volume of the working medium for any point of the indicator diagram. Considering negligible the irreversibility of changes of the working medium state during combustion process let us assume the invariability of the working medium mass . Apart from this circumstance, there are the others taken as a principle of existing technique [14]. Firstly, when estimating the index of heat capacity of the working medium it is assumed that in every instant of time of the working cycle the working medium consists of air and a final product of combustion, the presence and properties of intermediate product of burning reaction not being taken into account [15]. Secondly, the index of adiabatic curve as well as heat capacity cannot be determined exactly owing to its various values for combustion products and air, and for the majority of carbohydrates contained in the intermediate combustion products either [16]. Because of the above-mentioned reasons, the assumption that in every instant of time the working medium is considered as a mixture of air and a final product of combustion does not allow us to obtain a high-precision result when applying any of the known methods of heat-generation analysis for indicator diagrams [17].
The basis of CNIDI technique for processing indicator diagrams is the assertion that the amount of heat generated in fuel combustion is composed of the sum of generated heat and heat loss to warming cylinder walls [18]. The technique implies a number of assumptions, such as considering the working medium as a mixture of air and final products of fuel combustion where it is not taken into account intermediate products of burning and heat loss to dissociation of combustion products and burning incompleteness as well as working medium leakage from a cylinder during the process of fuel burning. Mole mass of the working medium is assumed as constant and equal to mole mass of air, 29 kg/kilomole; specific isochoric heat capacity of the working medium is considered a quasiconstant value which is determined for every design moment of time of the rotation angle of a crankshaft, and its derivative on the rotation angle of a crankshaft is assumed as being equal to zero [19].
The major design operations performed during the implementation of CNIDI techniques consist of processing of an indicator diagram. Starting from the separation point of a firing line from a compression curve, the amount of heat injected to the working medium is calculated for every small diagram section. The amount of heat baffled to cylinder walls is determined as well. These operations are performed for Along with the above examined assumptions it is worth noting instrumental errors of measuring devices such as presence of waves of pressure and reflection along an indicator diagram [20]. These negative phenomena are caused not by the nature of combustion process but by transmission of direct and return pressure waves in a channel connecting a pressure sensor to a hollow of a combustion chamber. As a result of above errors the calculated characteristics can assume negative values. Meanwhile the analysis precision of delayed burning occurring in conditions of air oxygen deficiency determines the quality level of investigation and diagnosis of the working process of an engine sufficiently.
In connection with above mentioned circumstances the neutralization of influence of studied measurement inaccuracy is undergone a smoothing procedure at the fuel delayed burning phase.
Smoothing is implemented beginning from counting step where the first negative value of heat generation is obtained by a mean-value method.
Multiple smoothing is performed from the last section of characteristic's wave where a positive value of heat generation occurs to a similar last section of the next wave with positive value.

Results and discussion
The scientists of Vyatka State University developed the program for personal computers using Javaprogramming which included Java Development Kit (JDK) by means of JDK and standard note-pad where recording, running and compiling Java code take place, Java Runtime Environment (JRE) where the mechanism of distributing software consists of self-contained virtual Java machine, Java Class Library and tools of its configuration, and Integrated Development Environment (IDE) where tools that help run, edit and compile codes are available. The program enables gaining heat generation law based on the data obtained by indicator diagrams experimentally [21].  A fragment of an indicator diagram of a diesel which was obtained experimentally is shown on figure  1. The diagram is 4Ч 10,5/12,0-sized of Д245.5S2 model read under nominal rotation speed of a crankshaft n=1800 min-1 by means of specialized control-recording equipment which consists of a transducer of static-dynamic pressure PS-01, an amplifier and signal converter AQ-02-001, and modular system of data acquisition NICOMPACTDAQ.
The program interface where source data entry is taken place is shown on figure 2, figure 3 and figure  4.
A fragment of obtained data of heat-generation values by means of the developed program for processing indicator diagrams according to CNIDI technique is shown on figure 5.    Operational experience with the developed program shows that applying the proposed method in comparative analysis of heat generation dynamics is justified. It particularly concerns the cases when the conditions of heat transfer from gases to cylinder walls can be considered constant.

Conclusions
The analysis of available methods and techniques for determining heat-generation values of combustion engines is conducted.
It is found that applying the technique of processing experimental indicator diagrams is one of the most reliably describing processes occurring in diesel cylinders.
The analysis of theoretical basic of fuel combustion process by means of experimental indicator diagrams is conducted; taking into account imprecision in source data is considered; the ways of correcting these data are proved.
A computer program is developed by means of the techniques for calculating heat-generation characteristic under burning conditions according to the given diagrams.
Actual practice demonstrated that applying the proposed CNIDI techniques and the appropriate program for analysis indicator diagrams provides the desired quality of results investigating the influence of various factors on the fuel combustion process in an engine.