WO2009144431A1

WO2009144431A1 - Temperature sensor for monitoring exhaust gases

Info

Publication number: WO2009144431A1
Application number: PCT/GB2008/001795
Authority: WO
Inventors: Anthony Paul Roskilly
Original assignee: University Of Newcastle Upon Tyne
Priority date: 2008-05-27
Filing date: 2008-05-27
Publication date: 2009-12-03

Abstract

A temperature sensor (34) for determining the temperature of exhaust gases of a diesel engine is disclosed. The temperature sensor comprises a silicon support (46) and a thin electrically conducting platinum layer (36) separated from the substrate by a silicon nitride layer (44). Changes in electrical resistance of the platinum layer as a result of changes in the temperature of exhaust gases expelled from the engine and coming into contact with the platinum layer can be rapidly measured to provide diagnostic information on engine performance.

Description

TEMPERATURE SENSOR FOR MONITORING EXHAUST GASES

The present invention relates to a temperature sensor for monitoring engine gas exchange and combustion processes for internal combustion engines, and relates particularly, but not exclusively, to temperature sensors for monitoring the temperature of exhaust gases from diesel engines. The invention also relates to an internal combustion engine provided with such a sensor, and to a method of monitoring and control of an internal combustion engine.

In the last few decades, power output from diesel engines has increased steadily, particularly for slow speed diesel engines and primarily in order to meet the high propulsion power demand of large container ships. As a result, manufacturers of diesel engines have increased the power density (output per cylinder) and reduced the specific weight of diesel engines significantly, and have also sought to reduce specific fuel oil consumption, which influences the direct operating costs. A reduction in specific fuel oil consumption can be achieved by running each cylinder of the diesel engine at-.-a higher temperature closer to stoichiometric conditions where cycle temperatures are higher, and increase the volume .expansion ratio to achieve greater work output for a fixed heat input. This is achieved at an engine optimised point with near uniform air to fuel ratio across a combustion chamber of the engine, but at the expense of a smaller safety margin between normal operation and thermal overload of engine components. Operating the engine closer to its thermal overload condition reduces the operating life of combustion chamber components, and may in some circumstances cause catastrophic failure of such components. Some faults associated with engine gas exchange and fuel combustion may not cause a thermal overload condition but result in the engine operating with poor fuel efficiency and/or high harmful exhaust gas emissions. To maintain an engine at an optimum operating condition requires effective engine gas exchange and combustion processes through the control of the turbocharging, exhaust valve timing and fuel injection processes.

The proximity of a diesel engine operation to a thermal overload condition and other engine gas exchange and fuel combustion faults can in some circumstances be detected from temperature changes of gases exhausted from a combustion chamber of the engine. Control of the gas exchange and combustion processes can be improved by monitoring temperature changes of exhaust gases. Temperature sensors for such gases are known which comprise robust thermocouples. However, such thermocouples suffer from the drawback that the thermal mass of thermocouples which are sufficiently robust to be useable for monitoring the temperature of exhaust gases from diesel engines is so large that the response time of the thermocouple is too long to enable the thermocouple to adequately monitor rapidly changing temperatures of exhaust gases.

Preferred embodiments of the present invention seek to improve the extent to which rapidly changing temperatures of exhaust gases from an internal combustion engine can be monitored.

According to an aspect of the present invention, there is provided a temperature sensor for determining the temperature of exhaust gases of an internal combustion engine, the temperature sensor comprising a support and at least one electrically conducting layer having an electrical property dependent upon temperature.

By providing a temperature sensor comprising a support and at least one electrically conducting layer having an electrical resistance dependent upon temperature, this provides the advantage of enabling a robust sensor having a temperature dependent conductive layer of low thermal mass to be constructed, which in turn enables the sensor to monitor rapidly changing temperatures .

At least one said electrically conducting layer may have an electrical resistance dependent upon temperature.

At least one said electrically conductive layer may include at least one metal .

At least one said electrically conductive layer may include at least one metal oxide and/or at least one metal nitride .

At least one said metal may include at least one of platinum, gold, iridium, rhodium, niobium, tantalum, tungsten, molybdenum, palladium, vanadium and/or alloys and/or mixtures thereof.

At least one said electrically conducting layer may include two metals forming at least one thermocouple.

Said support may include silicon. By forming the support from silicon, this provides the advantage of enabling parts of the support to be etched away to maximise exposure of at least one said electrically conductive layer to exhaust gases to be monitored, and to also minimise the effect of the thermal mass of the substrate with that of the or each electrically conductive layer .

At least one said electrically conductive layer may have a meandering structure.

By providing at least one electrically conductive layer having a convoluted structure, for example by etching away part of the electrically conductive layer to provide an electrically conductive layer of undulating shape, this provides the advantage of enabling temperature resistant behaviour of the electrically conductive layer to be maximised .

The sensor may further comprise at least one thermal insulator member for resisting conduction of heat from at least one said electrically conducting layer to said support .

This provides the advantage of minimising the extent to which the thermal mass of the support affects that of the electrically conductive layer such that the support has a substantially reduced impact on the temporal response of the sensor to temperature changes .

At least one said thermal insulator member may include at least one oxide and/or nitride. At least one said thermal insulator member may include at least one of silicon oxide, silicon nitride, silicon oxynitride, aluminium oxide and/or aluminium nitride.

The sensor may further comprise at least one passivation layer for resisting corrosion of at least part of the sensor.

At least one said passivation layer may include at least one oxide and/or nitride and/or diamond and/or ceramic material and/or so-called Diamond-like carbon.

The sensor may further comprise at least one reference sensor element.

The sensor may further comprise at least one heating element .

This provides the advantage of enabling the sensor to be operated in an optimum temperature range providing the largest sensitivity to temperature changes.

At least one said heating element may be an electrical heating element located adjacent a said electrically conductive layer.

According to another aspect of the present invention, there is provided a data logging apparatus for logging operation data from an internal combustion engine, the apparatus comprising a temperature sensor as defined above, and data storage means for storing operation data from the engine and temperature data from the temperature sensor. According to a further aspect of the present invention, there is provided an internal combustion engine having at least one combustion chamber and at least one temperature sensor as defined above for monitoring the temperature of exhaust gases expelled from a respective said combustion chamber.

The engine may further comprise at least one oxygen sensor for monitoring oxygen content of exhaust gases expelled from a respective said combustion chamber.

This provides the advantage of enabling further diagnostic information relating to engine performance to be obtained.

The engine may further comprise control means for controlling operation of the engine in response to inputs from at least one said temperature sensor and/or at least one said oxygen sensor.

This provides the advantage of enabling engine timing to be controlled to minimise harmful effects of conditions detected by at least one said temperature sensor and/or at least one said oxygen sensor.

According to a further aspect of the present invention, there is provided a method of monitoring operation of an internal combustion engine having at least one combustion chamber, the method comprising monitoring temperature of exhaust gases expelled from at least one said combustion chamber by means of at least one temperature sensor as defined above. The method may further comprise the step of determining oxygen content of exhaust gases expelled from at least one said combustion chamber.

The method may further comprise the step of controlling operation of the engine in response to inputs from at least one said temperature sensor and/or at least one said oxygen sensor.

Preferred embodiments of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which : -

Figure 1 is a schematic view of a diesel engine embodying the present invention;

Figure 2 is a perspective view of a temperature sensor embodying the present invention for use in the engine of Figure 1;

Figure 3 is an exploded view of the temperature sensor of Figure 2 ;

Figure 4 is a plan view of part of a first embodiment of the sensor of Figure 2 ;

Figure 5 is a cross sectional side view of the part of the sensor shown in Figure 4;

Figure 6 is a cross sectional side view, corresponding to Figure 5, of part of a second embodiment of the sensor of Figure 2; Figure 7 is a plan view, corresponding to Figure 4, of the part of the sensor shown in Figure 6;

Figure 8 is a plan view, corresponding to Figure 7, of a part of a third embodiment of the sensor shown in Figure 2;

Figure 9 shows a schematic view of a combustion test rig for testing thermal overload conditions of components of the engine of Figure 1 ;

Figure 10 is a schematic cross-sectional view of a temperature sensor of a fourth embodiment of the present invention;

Figure 1OA is a schematic plan view of the sensor of Figure 10;

Figure 11 shows the relationship between adiabatic flame temperature and exhaust gas oxygen concentration and the excess air factor in the engine of Figure 1;

Figure 12 shows the relationship between exhaust gas temperature and overall excess air ratio and the trapped excess air ratio of a combustion flame in the test rig of Figure 9;

Figure 13 shows the correlation between oxygen concentration and crank angle for cylinders of the diesel engine of Figure 1; Figure 14 shows the relationship between exhaust valve timing and crank angle in the diesel engine of Figure 1;

Figure 15 provides an indication of piston crown wear rate in the engine of Figure 1;

Figure 16 shows the relationship between temperature of exhaust gases and crank angle in the engine of Figure 1;

Figure 17 shows the relationship between oxygen concentration in exhaust gases and crank angle in the engine of Figure 1; and

Figure 18 shows the relationship between percentage oxygen in exhaust gases, air demand and excess air factor when air temperature is at 100⁰C at start of compression of the engine of Figure 1.

Referring to Figure 1, a diesel engine 1 has a combustion chamber 2 defined by a cylinder 3 having a fuel injection apparatus 4, an air inlet 5, and an exhaust gas outlet 6 having an exhaust gas valve 7. The fuel injection apparatus 4 is controlled by means of an engine fuel injection control unit 8, supervised by an engine control and monitoring unit 9. Air is supplied to air inlet 5 by means of a turbocharger 10 controlled by a turbocharger control unit 11, also supervised by engine control and monitoring unit 9. The exhaust gas valve 7 opening and closing is controlled by a exhaust valve control unit which is also supervised by an engine control and monitoring unit 9 such that the engine air and exhaust gas exchange and the quantity and timing of fuel injected into the combustion chamber 2 is synchronised with movement of a piston 12, measured using a crank angle sensor 13, in the cylinder 3 to ensure correct combustion, in a manner which will be familiar to persons skilled in the art.

A temperature sensor 26, which will be described in greater detail below, is located in exhaust gas outlet 6 adjacent the exhaust gas outlet valve 7, and an oxygen sensor 14 is located in the exhaust gas outlet 6 for analysing the content of the exhaust gases expelled from the combustion chamber 2. Output signals from the temperature sensor 26 and oxygen sensor 14 are input to the engine control and monitoring unit 9 to enable the performance of the engine to be monitored and the timing of the engine to be controlled in response to the information derived from the temperature sensor 26 and oxygen sensor 14. The oxygen sensor 14 may be a commercially available oxygen sensor familiar to persons skilled in the art, for example a sensor provided by Robert Bosch GmbH.

Referring to Figures 2 and 3, the temperature sensor 26 has a tubular housing 30 for location in the exhaust gas outlet 14 in such a manner that exhaust gases in the vicinity of the radial centre of the exhaust gas outlet 14 which are expelled from the combustion chamber 4 of the engine 2 enter a slot 32 in the housing 30 in the direction of arrow A shown in Figure 2. The temperature sensor 26 has a sensor element 34 including a thin platinum layer 36 (Figure 5) having an electrical resistance dependent upon temperature, such that the electrical resistance of the platinum layer 36 rapidly tracks fluctuations in the temperature of exhaust gases passing over the sensor element 34. The sensor element 34 is attached to the housing 30 by means of springs 38, and a protective cover 40 is mounted over the sensor element 34 by means of screws 42 to form the slot 32.

As shown in greater detail in Figures 4 and 5, the sensor element 34 is formed by forming a barrier layer 44 of thermally insulating silicon nitride on a silicon substrate 46, and then forming the platinum resistive layer 36 on the silicon nitride layer 44 and etching away part of the platinum layer 36 to form a convoluted or meandering resistive platinum sensor 48 and platinum leads 50 for obtaining electrical signals from the sensor 48. Part of the silicon substrate 46 is also etched away to provide a gap 52, which minimises the extent to which the thermal mass of the silicon substrate 46 in proximity to the platinum sensor 48 increases the response time of the sensor 48 to changes in ambient temperature. Gold contact pads 54 are formed on the silicon nitride layer 44 to enable the sensor element 34 to be connected to output leads (not shown) .

Figures 6 and 7 illustrate a second embodiment of sensor element 134, and parts common to the embodiment of Figures 4 and 5 are denoted by like reference numerals but increased by 100. The sensor element 134 of Figures 6 and 7 is formed in a similar manner to the embodiment of Figures 4 and 5, i.e. by forming a silicon nitride layer 144 on a silicon substrate 146 and forming a platinum layer 136 on the silicon nitride layer 144. The platinum layer 136 is then partly etched away to form a resistive platinum temperature sensor 148 connected to platinum leads 150, and a platinum reference sensor 160 connected to platinum leads 162. Gold conductive pads 154 are formed on the platinum layer 136 to contact platinum leads 150, 162, and the platinum layer 136 is protected from corrosion by a first passivation layer 164 of diamond like carbon formed over the temperature sensor 148, and a second passivation layer 166 of silicon nitride surrounding the first passivation layer 164.

Figure 8, in which parts common to the embodiment of Figures 4 and 5 are denoted by like reference numerals but increased by 200, shows a third embodiment of sensor element 234 in which a platinum heater element 270 is formed together with platinum temperature sensor 248. The heater element 270 is connected to platinum lead 272 to enable electrical heating of the sensor 248 to enable the sensor 248 to operate in a temperate range providing the largest sensitivity to changes in ambient temperature.

Figures 10 and 1OA show a temperature sensor of a further embodiment of the invention, in which the platinum layer 36 of Figure 2 is replaced by a double layer 336, 336a formed from two different metals, such as platinum and rhodium, or tungsten and rhenium, or one or more alloys of those metals, such that the metals or metal alloys act as a thermocouple 338 at the junction of the metals and generate a voltage dependent on temperature of exhaust gases coming into contact with the sensor.

Thermal overload can be defined as a condition in which design threshold values such as surface temperature of combustion chamber components is exceeded. This can result in a reduction of the operating life of the component, or in catastrophic failure as a component. A brief explanation of how the output signals from the temperature sensor of Figures 2 to 5 can be used to diagnose thermal overload of engine components will now be provided .

Thermal overload is related to several engine parameters, for example:

(i) in cylinder trapped excess air ratio; (ii) charge pressure in relation to amount of fuel inj ected;

(iii) ratio of total/in cylinder trapped excess air ratio;

(iv) maximum spatial average temperature in the cylinder;

(v) cylinder temperature just before opening of the exhaust;

(vi) gas temperature directly after exhaust valve; (vii) exhaust gas receiver temperature.

Variations in the trapped air to fuel ratio within the cylinder can affect the useful life of combustion chamber components. Consequently, deterioration in performance of components responsible for maintaining the required air to fuel ratio can cause the engine to overload thermally. Examples of such components are turbochargers, piston crowns and rings, cylinder liners, inlet and exhaust valves, scavenge valves and fuel injection systems. The effects of malfunction of some of these components such as turbochargers are universal to the engine, causing

"universal thermal overload", i.e. thermal overload of the entire engine, whereas some of the other components are cylinder specific and their failure causes "differential thermal overload", for example delayed closing of an exhaust valve in a two-stroke engine.

The surface temperature of each component is governed by heat influx and heat outflux from the material. An increase in heat influx or decrease in heat outflux will raise the surface temperature above the threshold value, and an increase in heat influx will depend on the temperature of gas close to the component surface, which in turn is a function of the air to fuel ratio. Figure 11 shows the adiabatic flame temperature with dissociation for an end of compression temperature of 500⁰C and exhaust gas oxygen concentration for different values of Lambda. The flame temperature is seen to be highest at stoichiometric conditions, and reduces with increase in excess air ratio. For excess air ratios of less than 1, i.e. sub- stoichiometric conditions, the flame temperature will be lower than that for stoichiometric conditions .

For most diesel engines, the air to fuel ratio is not uniform across the combustion space in the combustion chamber 2, as a result of which non-uniform temperatures arise across the piston crown. In theory, the maximum flame temperature is observed at Lambda =1, but in practise, as a result of non-uniformity in the air fuel mixture, this occurs at approximately Lambda =1.2. An engine operating with Lambda =1.2 will have its combustion chamber components running hotter than those operating at a greater value of Lambda. It is believed that for sub- stoichiometric conditions, the lack of active radicals present in the combustion zone slows down the flame propagation rate, causing a voluminous flame which comes into contact with the combustion chamber components, thus increasing the rate of heat flux, as opposed to a lean burn condition in which the flame is compact, with a cushion of air between the flame and the components surface, which is therefore at a much lower temperature.

Figure 9 shows a schematic diagram of a combustion test rig 300 used for testing thermal overload conditions. The test rig 300 has a primary combustor 302 having a fuel inlet 304 connected to a fuel injection system 306, a first air inlet 308, air first air deliver system 310, and a first exhaust outlet 312 connected to a first exhaust gas sampling line 314. The rig 300 also has a secondary combustor 316 connected to the primary combustor 302, which has second air inlets 318 connected to a second air delivery system 320, and a second exhaust gas outlet 322 connected to a second exhaust gas sampling line 324. The first and second exhaust gas sampling lines 314, 324 are connected to an exhaust gas emission analyser 326 including a conventional oxygen sensor and a temperature sensor.

The primary combustor 302 is operated with a rich fuel/air ratio and produces a mixture of carbon monoxide and carbon dioxide, and the secondary combustor 316, positioned just behind the primary combustor 302, is supplied with further air through air inlets 318 to burn all of the carbon monoxide to form carbon dioxide. Sub- stoichiometric conditions in the primary combustor 302 are achieved by maintaining the air flow rate substantially constant while increasing the fuel flow rate. It is observed during tests that by increasing the level of sub- stoichiometric condition, the flame lift off distance from the burner increases, and the flame becomes more voluminous . The structure of a flame at various excess air ratios can be explained with reference to Figure 12. If the primary combustor 302 of the test rig 300 is considered as equivalent to the combustion space of a diesel engine, and the location of the exhaust temperature probe 324 at the outlet is considered equivalent to the position of any critical combustion chamber component, such as a piston crown or cylinder liner, as mentioned above, if the fuel rate is increased at constant air mass flow rate, the excess air ratio decreases, and a decrease in adiabatic flame temperature is observed as the entire energy from the fuel fails to be released because of partial oxidation of carbon. However, if the reaction slows down as a result of lack of active radicals, the flame becomes voluminous, and this is observed by an increase in the temperature of exhaust gases at the outlet probe 326. The temperature at the probe 326 was found to increase from 775°C to 1000⁰C with excess air ratio changing from 1.12 to 0.71. Such high temperature flue gas in contact with any combustion chamber component would be expected to result in an increased rate of heat transfer through the component, and consequent failure of the component.

It is also possible to maintain the overall excess air ratio approximately constant for different primary chamber excess air ratios. This demonstrates the possibility of "differential thermal overload", as discussed above, even if the overall air to fuel ratio is above the threshold value for universal thermal overload. Since the air to fuel ratio across the combustion space is not uniform, a reduction in the average trapped air to fuel ratio would be expected to create local regions with stoichiometric or sub-stoichiometric conditions that would result in a voluminous flame and local hotspots.

For a diesel engine with constant injection timing and expansion ratio, a high adiabatic flame temperature would result in a high exhaust gas temperature and low oxygen concentration. This provides the possibility of predicting the size of the flame based on oxygen concentration and temperature of the blow down gas. In other words, the oxygen concentration and temperature characteristics of exhaust gases from the engine enable thermal overloading of the engine components to be identified. In order to prevent parts of the combustion chamber components from running above their threshold temperatures, it is advisable to have at least 8% oxygen in the blow down gas, which corresponds to Lambda =1.7. For a slow speed two stroke engine which relies solely on the differential pressure between scavenge and exhaust manifolds to remove the residual gas and charge the cylinder with fresh air, it is desirable to have one part of air in excess of the trapped Lambda to clean the cylinder.

As a result of the use of the temperature sensor of Figures 2 to 5, improved insight into the gas exchange process is provided, which enables better analysis and prediction of the quality of combustion. If the trapped air to fuel ratio is close to stoichiometric conditions, slow burning as a result of non availability of sufficient reactive species can result in a high exhaust gas temperature. This can be detected from a sharp rate of temperature rise at the start of the gas exchange process, indicating a much higher temperature compared to the mean exhaust temperature. If the expansion ratio is constant, a higher flame temperature as a result of slow burning would mean higher exhaust temperature. Similarly if there is a loss of fresh air towards the end of the gas exchange process, the temperature sensor would be expected to come into contact with low temperature air which will be indicated by a sharp reduction in temperature. The amplitude of this cyclic variation in temperature may be regarded as an indicator of combustion air lost at the end of the gas exchange process, which results in a lower trapped air to fuel ratio. A direct relationship can therefore be established between the oxygen concentration in the exhaust gases and the temperature peak reached during this process. The provision of the sensor of Figures 2 to 5 enables these parameters to be more easily detected than with conventional sensors, or in conditions in which they can not be detected at all using conventional sensors .

The results of a diagnostic test of a slow speed diesel engine having cylinders suffering from differential thermal overload in the form of differential piston crown burning are shown. The engine was tested by means of oxygen sensors fitted on the duct between the exhaust valve housing and the constant pressure exhaust manifold, proximity sensors mounted on the exhaust valve to measure valve timing, and a temperature sensor as described with reference to Figures 2 to 5 was placed in the exhaust gas stream. The results of tests carried out on four cylinders of the engine are shown in Figure 13, which shows the relationship between oxygen concentration in the exhaust gas and piston crank angle. Figure 14 shows the relationship between exhaust valve timing and crank angle for the individual cylinders, and it can therefore be inferred from Figures 13 and 14 that a cylinder with late exhaust valve closing has the lowest oxygen concentration in its blow down gas, indicating loss of charge air.

Figure 15 shows measurement of piston crown wear rate by means of a template conforming to bulge geometry of a new piston crown. It is found that the minimum concentration of oxygen can be correlated to the piston crown burn rate as a result of the high rate of heat transfer from a voluminous flame. Referring to Figures 13 and 15, cylinder 4 is found to have the lowest oxygen concentration and the highest relative piston crown wear rate, and cylinder 5 is found to have the highest oxygen concentration and lowest relative piston crown wear rate. Cylinders 6 and 7, having oxygen concentrations of 4.5% and 5.0% respectively, also follow a trend of less oxygen in the exhaust gases corresponding to higher piston crown burning rate .

Figures 16 and 17 show a coloration between exhaust gas temperature and oxygen concentration, from which is can be established that a lower oxygen concentration in the exhaust gas corresponds to a higher exhaust gas temperature. The lowest cyclic variation and lowest peak exhaust temperature suggest that there is minimal or no combustion air loss at the end of the scavenging process, which results in a high trapped air to fuel ratio, as in the case of cylinder 1.

Figure 18 shows the results of theoretical calculations carried out on a slow speed diesel engine operating at 68 rpm to predict the effect of late exhaust valve closure on the trapped air to fuel ratio. Delayed closing of exhaust valve reduces the trapped air to fuel ratio, which can be indicated by a lower oxygen concentration in the exhaust gas. Also, a lower tapped air to fuel ratio may be as a result of malfunctioning of a component involved in the gas exchange process.

As a result of the provision of the sensor of Figures 2 to 5, the onset of thermal overload can be predicted, and tests on a slow speed diesel engine have been able to identify the cause of accelerated piston crown burn rate. It can be concluded that the size of the flame is a function of the air to fuel ratio which can be linked to the amount of residual oxygen left in the exhaust gases. The high surface temperature of a combustion chamber component may be due to a voluminous flame, which increases the rate of heat transfer. Cylinders with the lowest oxygen concentration in the exhaust gas and the highest cyclic fluctuation in exhaust gas temperature are found to have the highest burn rate, and cylinders with the lowest oxygen concentration also had delayed closing of the exhaust valves, resulting in loss of air from the cylinder which reduced the trapped air to fuel ratio.

It will be appreciated by person skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, instead of forming the temperature sensor using etching techniques, one or more of the metal layers may be formed by means of a lift-off process which will be familiar to persons skilled in the art. In addition, instead of forming the support for the temperature sensor from silicon, the support may comprise aluminium on which an oxide membrane has been grown, such as by anodisation, facilitating selective removal of the aluminium from the underside of said membrane by chemical etching.

Claims

1. A temperature sensor for determining the temperature of exhaust gases of an internal combustion engine, the temperature sensor comprising a support and at least one electrically conducting layer having an electrical property dependent upon temperature.

2. A temperature sensor according to claim 1, wherein at least one said electrically conducting layer has an electrical resistance dependent upon temperature.

3. A temperature sensor according to claim 2, wherein at least one said electrically conductive layer includes at least one metal.

4. A temperature sensor according to claim 2 or 3, wherein at least one said electrically conductive layer includes at least one metal oxide and/or at least one metal nitride.

5. A temperature sensor according to claim 3 or 4 , wherein at least one said metal includes at least one of platinum, gold, iridium, rhodium, niobium, tantalum, tungsten, molybdenum, palladium, vanadium and/or alloys and/or mixtures thereof.

6. A temperature sensor according to any one of the preceding claims, wherein at least one said electrically conducting layer includes at least two metals forming at least one thermocouple.

7. A temperature sensor according to claim 6, wherein at least one said thermocouple includes at least one metal alloy .

8. A temperature sensor according to claim 6 and 7, wherein at least one said electrically conducting layer includes platinum and rhodium and/or tungsten and rhenium.

9. A temperature sensor according to any one of the preceding claims, wherein said support includes silicon.

10. A temperature sensor according to any one of the preceding claims, wherein at least one said electrically conductive layer has a meandering structure.

11. A temperature sensor according to any one of the preceding claims, further comprising at least one thermal insulator member for resisting conduction of heat from at least one said electrically conducting layer to said support .

12. A temperature sensor according to claim 11, wherein at least one said thermal insulator member includes at least one oxide and/or nitride.

13. A temperature sensor according to claim 11, wherein at least one said thermal insulator member includes at least one of silicon oxide, silicon nitride, silicon oxynitride, aluminium oxide and/or aluminium nitride.

14. A temperature sensor according to any one of the preceding claims, further comprising at least one passivation layer for resisting corrosion of at least part of the sensor.

15. A temperature sensor according to claim 14, wherein at least one said passivation layer includes at least one oxide and/or nitride and/or diamond and/or ceramic material and/or so-called Diamond-like carbon.

16. A temperature sensor according to any one of the preceding claims, further comprising at least one reference sensor element.

17. A temperature sensor according to any one of the preceding claims, further comprising at least one heating element.

18. A temperature sensor according to claim 17, wherein at least one said heating element is an electrical heating element located adjacent a said electrically conductive layer.

19. A data logging apparatus for logging operation data from an internal combustion engine, the apparatus comprising a temperature sensor according to any one of the preceding claims, and data storage means for storing operation data from the engine and temperature data from the temperature sensor.

20. An internal combustion engine having at least one combustion chamber and at least one temperature sensor according to any one of claims 1 to 18 for monitoring the temperature of exhaust gases expelled from a respective said combustion chamber.

21. An engine according to claim 20, further comprising at least one oxygen sensor for monitoring oxygen content of exhaust gases expelled from a respective said combustion chamber.

22. An engine according to claim 20 or 21, further comprising control means for controlling operation of the engine in response to inputs from at least one said temperature sensor and/or at least one said oxygen sensor.

23. A method of monitoring operation of an internal combustion engine having at least one combustion chamber, the method comprising monitoring temperature of exhaust gases expelled from at least one said combustion chamber by means of at least one temperature sensor according to any one of claims 1 to 18.

24. A method according to claim 23, further comprising the step of determining oxygen content of exhaust gases expelled from at least one said combustion chamber.

25. A method according to claim 23 or 24, further comprising the step of controlling operation of the engine in response to inputs from at least one said temperature sensor and/or at least one said oxygen sensor.