The use of thermography in the diagnosis of ship piston internal combustion engines

The intensity of infrared radiation emitted by objects depends mainly on their temperature. One of the diagnostic signals may be the temperature field. In infrared thermography, this quantity is used as an indicator of the technical condition of marine objects. The article presents an overview of the use of infrared thermography for the diagnosis mainly of marine piston floating objects and various types of reciprocating internal combustion engines as well as examples of own research results. A general introduction to infrared thermography and common procedures for temperature measurement and non-destructive testing are presented. Experimental research was carried out both in laboratory conditions and in the operating conditions of sea-going vessels. Experimental studies consisted of the presentation of photographs of the same objects made in visible light and the use of infrared thermography. The same objects were also compared, but for different cylinders of the tested internal combustion engines as well as for the up state and fault state. The characteristics of the temperature values at selected points were taken depending on the engine load along with the approximation mathematical models of these dependencies.


Introduction
Infrared thermography is a technique for producing an image of the invisible to eyes infrared light emitted by objects due to their thermal condition. A typical a thermography camera produces a live video picture of heat radiation intensities. More sophisticated cameras can actually measure the temperature values of any object or surface in the fieldof-view and produce colour images that make interpretation of thermal patterns easier. An image produced by an infrared (IR) camera is called a thermogram [1].
The properties of measuring heat transmission from objects using the thermography camera are more than an interesting novelty. An advance in IR sensor production has helped the infrared viewing technology to be adopted as a cost-effective, non-invasive measuring method. Advanced optics and sophisticated software interfaces continue to add to the variety of Thermal IR cameras.
However, the most powerful means of thermal energy transfer is radiation, which moves at the speed of light. Infrared energy is emitted by all materials above 0 K. Infrared radiation is part of the electromagnetic spectrum and occupies frequencies between visible light and radio waves. The infrared part of the spectrum spans wavelengths from 0.7 μm to 1000 μm [1]. Within this wave band, only frequencies of 0.7 μm to 20 μm are used for practical, everyday temperature measurement.
The three methods by which heat flows from one object to another are: radiation, convection and conduction. These three phenomena in most situations they occur together. The invention of the thermal imaging camera has caused a number of changes in the field of temperature measurement. The measurement method bases its operation on the phenomena of the objects' impact relative to their surrounding space. The use of imaging and it has been possible to detect the fuel vapour and the burned gas motion in the combustion chamber for a longer period with respect to visible range. CO2 evolution in the available volume during several combustion phases has been detected: during the inlet phase, during the combustion phase, in the burned gases cloud that moves toward the outlet valves. The results obtained suggest IR diagnostics as useful tool for engine control.
Infrared thermography has become the powerful tool for basic and applied scientific research and for the application in maritime affairs. As a prognosis maintenance tool [9], IR thermography has the ability to identify problems before they occur. It is especially helpful for trouble shooting potential electrical overloads, worn or bad circuit breakers. IR thermography can also be used to detect bad bearings of shafts or any application where heat detection would be beneficial. This paper has basic principles of IR thermography are presented and examples of the tool application in maritime affairs are given [1].
One of the benefits of using thermal imaging is the ability to predict possible the fire hazards due to increases in temperature in controlled areas in a particular marine object. The work proposes the possibility of applying new electronic and computer technology as part of the ship's fire detection system, such as the use of computer vision, using existing marine thermography systems and installing thermal imaging IR cameras on the same system [5]. There has been proposed communication between the thermal imaging system and the fire detection and central alarm system of the ship. The visual analysis of certain areas on board the ship and the related facilities inside it, with the addition of certain software applications into the existing video technology system, makes is the fire alarm system. With the forecast and send early warnings to the ship's central fire alarm system, thereby contributing to improved safety with to equipment, the ship as a whole, cargo and human lives. The spreads widely very fastly in high temperatures and becomes the cause of great damage to ship equipment [10], often resulting in the loss of the ship. Videotapes from thermal cameras can be used for risk analysis and the prevention of future ship fire incidents. It is possible the fast detection of temperature changes very early warning.
The article presented non destruction method and results of using thermal method in diagnostic of marine combustion engines operation of fishing fleet vessel [7]. The article presents a mathematical model for determining the temperature distribution by means of thermovision [5]. Knowledge of this model makes it possible to analyse the influence of external factors [11] on the accuracy of temperature determination by thermovision.

Principles of Infrared Thermography
The basic dependence used to determine the temperature is the thermovision method is basic equation of radiation. Effective radiation power of the thermographic camera that reaches the lens from the surface of the object being examined consists of the following components [12]:  the effective radiation power emitted by the tested object,  radiation of the background reflected from the object,  radiation of your own atmosphere.
The hotter an object becomes the more infrared energy it emits. The Stefan-Boltzmann law, states that the total energy radiated per unit surface area of a black body in unit time EBB is directly proportional to the fourth power of the black body absolute temperature T: The constant of proportionality σ, called the Stefan-Boltzmann constant is nonfundamental in the sense that it derives from other known constants of nature.
When the object is at thermal equilibrium, the amount of absorption will equal the amount of emission. The Kirchoff's law determined for any material, the emissivity and absorptance of the body are equal at any specified temperature and wavelength [3]: ε = a (2) where: When the infrared energy radiated by real object reaches another body, a portion of the energy received will be absorbed a, a portion will be reflected r and, if the body is not opaque, a portion tr will be transmitted. The sum of the individual parts is added up to the initial value of radiation which left the source: a + r + tr = 1 (3) The total radiation received by the camera Wt comes from three sources: the emission of the target objects Eo, the emission of the surroundings and reflected by the object Er and the emission of the atmosphere Ea. It can be expressed as equation: (4) The total strength of the radiation can be expressed with the formula FLIR Systems: Wto = εoτoWo + (1 -εo)τWr + (1 -τa)Wa (5) where:

Wto = Eo + Er + Ea
εoτoWois the emission of radiation from the object, εothe emission of the object, τathe atmospheric release, (1 -εo)τWrthe reflection from the environment, (1 -εo)the reflection of the object, τaWrthe temperature of the environment; (1 -τa)Wathe emission of radiation from the atmosphere, (1 -τa) is the emission of the atmosphere and Wa is the temperature of the atmosphere.
The basic equation of radiation for the complexity of the measurement scene can be saved: Hence the measured temperature of object is equal: In order to solve equation (6), the following parameters must be supplied: the emissivity of the object, the reflected temperature Tr, the transmittance of the atmosphere and the temperature of the atmosphere Ta. The transmittance of the atmosphere is estimated using the distance from the object to the camera and the relative humidity. This value is very close to one. The temperature of the atmosphere is obtained using a common thermometer. However, as the emittance of the atmosphere is very close to zero (1 = a), this parameter has little influence on the temperature measurement. The emissivity of the object and the reflected temperature has but the very high influence on the temperature measurement.

Methodology and research objects
The object of thermal imaging studies were the combustion engines driving generators of 3 types and one main drive. The research was carried out both in the laboratory conditions of the Maritime University of Szczecin and in the conditions of operation of sea-going vessels. Different types of FIR cameras were used for the tests. First, the measuring track was tested by comparing the temperature readings with thermometers and the thermovision camera. Thermal imaging was preceded by the configuration of the camera settings to the conditions that prevailed during the tests, which is why the parameters of the reference conditions were measured: ambient temperature, atmospheric pressure and relative humidity.

Sample investigations results
The measurement path was calibrated by measuring the temperature with contactless and contactless devices inside the muffle furnace for calibrating thermoelectric thermometers and a thermal imaging camera (Fig. 1)  The tests were carried out for various cylinders of combustion engines, with different loads and for different technical conditions. In contrast, Fig. 6 shows dependencies the temperature of the injector bodies depending on the engine load. The curve for the third cylinder deviating from the others results from the inability state of the injection subsystem. This technique is based on the polynomial fit of each pixel time history from the given thermographic image sequence. The evolution of the temperature is adjusted to an n degree polynomial for input value x, what described in equation [13]: T(t) = anx n + an-1x n-1 + … + a1x + a0 (8) This paper presents an example of the polynomial model for the temperature dependence of the injector body function on the relative load RL of the combustion engine for one of the curves of Fig. 6. t = 0,3833RL 4 -5,0658RL 3 + 22,164RL 2 -28,479RL + 35,598 (9) 6 Conclusions Diagnostics of ship engine facilities using thermovision and thermography are noninvasive, which is likely to be recognized by classification societies. Application is possible for objects with different temperature fields. The measurement process itself takes place without any prior preparation and quickly.