The impact of the accuracy of indicator diagrams on the heat release characteristics calculation , used in the diagnosis of marine diesel engine

The paper analyzes the possibility to use the electronic type indicators in the diagnosis of marine engines. It has been shown that in-depth analysis of indicator diagrams would be useful – calculation of heat release characteristics. To make this possible, measuring indicated systems should meet a number of important requirements in or-der to ensure that they can be used for the diagnostic purposes. These includes: high precision sensors for the measurement of cylinder pressure, high speed and accuracy of measuring and recording of measured values. These also includes reliable determination of the top dead center piston (TDC). In order to demonstrate the impact of positional error TDC, simulation study was conducted in which indicated diagrams were used, obtained on a medium-speed four-stroke marine diesel engine type A25/30 and the low-speed two-stroke marine diesel engine type RTA76, Sulzer company.


Introduction
Nowadays many marine engine-rooms are additionally equipped with portable or stationary electronic indicators.Open (expanded) indicator diagrams are mainly analyzed -diagrams in a coordinate system p = f() (cylinder pressure p variation as a function of crank angle ).
Indicated parameters are the essential complement to the standard measurement parameters and diagnostic inference can be more reliable [1,2].
Measuring systems destined for indication should meet a number of important requirements to be met to ensure the possibility of their diagnostic use.These includes: high precision sensors for the measurement of cylinder pressure, high speed and accuracy of measuring and recording of measured values, a reliable determination of the top dead center piston (TDC).These and other important issues cylinder pressure measurement were highlighted in many publications [3][4][5][6].Compliance with these requirements is particularly important when will be determined based on the indicator diagram of heat release characteristics for diagnostic purposes [7][8][9][10].
At old-design sea cargo ships with conventional equipment, marine engines diagnostics are still made on the basis of an analysis of changes in the value of the measured parameters of the engine [7,11].Diagnostician is the ship's mechanic, who by analyzing changes in the measured parameters relative to their reference values, tries to determine the type of damage.Such action is subjective and usually inefficient, depending on the knowledge and experience of the marine engineer [5,12,13].

Direct and in-depth analysis of indicator diagrams in diagnostics
Increasingly for indicated marine engines, it is being used the electronic type indicator, which includes: the combustion pressure sensors in each cylinder, the angular position sensor crankshaft and microprocessors system used for processing and visualization of the results of the measurements.This indicator is easy to use, characterized by high accuracy and fast developing results.This device gives results indicated as the average of dozen cycles.All essential values are displayed on the screen, and in addition an open indicator diagram is presented.Mean indicated pressure is automatically served beside other parameters, based on our numerical integration.Figure 1 shows an example of an indicator diagram, obtained using the an electronic indicator.It is marked on the all important characteristic values.In addition to those indicated values in the figure, the mean indicated pressure and indicated power can be counted.
An important feature of electronic indicators is the ability to save the results in memory and play them after some time.This way, you can easily compare the graphs indicated which were performed at different times, which gives a fuller analysis capabilities [14][15][16].This is particularly important during comparing the reference indicator diagram drawn in good technical condition of the engine with a graph removed after a longer period of operation; then are visible all deviations from the norm.Figure 2 shows an example of one coordinate system p = f() two graphs -curve 1 and curve

Study of th DC locatio lculated h
C position e ermining the atly influence ue of the net ue heat release In order to sitional TDC, ich was use dium-speed f der laborator oke engine ty erating of the s Studies in lab t bench of L25/30.This nchronous gen oaded the wat water (brine oratories of t ynia Maritime d 5.This stan 73, fuel tank and registrat An importan electronic in measure the from Kistler (element 1 pressure in Autopsie-S Figure 6).In many cases, in order to obtain a reliable diagnosis is indicated in-depth analysis of these graphs based on calculated heat release characteristics.Then, however, it is essential to cylinder pressure measurement accuracythe accuracy of the indicator diagram, including the exact location of TDC in the diagram.
The analysis of the results indicates that the error location TDC to 1% results in a significant deviation of the net heat release maximum value and heat release rate, to a few percent (from 3.5% to 8%).

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