energies Article
Development of a Diesel Engine Thermal Overload Monitoring System with Applications and Test Results Sangram Kishore Nanda 1,2 , Boru Jia 2, *, Andrew Smallbone 2 and Anthony Paul Roskilly 2 1 2
*
Wärtsilä Services Switzerland Ltd., CH-8401 Winterthur, Switzerland;
[email protected] Sir Joseph Swan Centre for Energy Research, Newcastle University, Newcastle upon Tyne NE1 7RU, UK;
[email protected] (A.S.);
[email protected] (A.P.R.) Correspondence:
[email protected]; Tel.: +44-075-4783-9154
Academic Editor: Wenming Yang Received: 19 April 2017; Accepted: 14 June 2017; Published: 22 June 2017
Abstract: In this research, the development of a diesel engine thermal overload monitoring system is presented with applications and test results. The designed diesel engine thermal overload monitoring system consists of two set of sensors, i.e., a lambda sensor to measure the oxygen concentration and a fast response thermocouple to measure the temperature of the gas leaving the cylinder. A medium speed Ruston diesel engine is instrumented to measure the required engine process parameters, measurements are taken at constant load and variable fuel delivery i.e., normal and excessive injection. It is indicated that with excessive injection, the test engine is of high risk to be operated at thermal overload condition. Further tests were carried out on a Sulzer 7RTA84T engine to explore the influence of engine operating at thermal overload condition on exhaust gas temperature and oxygen concentration in the blow down gas. It is established that a lower oxygen concentration in the blow down gas corresponds to a higher exhaust gas temperature. The piston crown wear rate will then be much higher due to the high rate of heat transfer from a voluminous flame. Keywords: diesel engine; thermal overload; monitoring system; thermocouple; lambda; wear rate
1. Introduction 1.1. Engine Thermal Overload The last couple of decades has seen a steady improvement of the power output from slow speed diesel engines with increase of propulsion power demands [1–3]. This has pushed engine researchers to increase the engine power density and reduce the specific fuel oil consumption (SFOC) [4,5]. An increase in power output from the cylinder results in an increase in fuel consumption. And the SFOC reduction can be achieved by operating the engine closer to stoichiometric conditions and keeping all the other parameters unchanged [3]. This has resulted in a reduction in design margins for the engines with higher component temperatures. However operating the engine closer to a thermal overload condition will reduce the operating life of combustion chamber components and may cause catastrophic failure in some instances [6,7]. 1.2. Current Engine Monitoring Technology Development As diesel engine technology is advancing, increased use of use of analytical methods has proven necessary to establish monitoring techniques able to predict performance and identify faults in the engine. The most common parameters used to monitor the thermodynamic performance of an engine
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are pressure and temperature at various points on the cycle, which can be found widely in the literature around engine research [8–13]. The most widely used technique for in-situ monitoring is a pressure volume trace, a technology historically referred to as an indicator card [14–17]. It is used to calculate the indicated power developed by a cylinder and when used with a light spring version, visualises the gas exchange process. The indicator instrument is used to obtain an out of phase diagram, commonly referred to as ‘draw card’, which helps detect faults during the injection and combustion period. This technique can fail to indicate certain faults in the thermodynamic process. It is because the technique relies on measuring pressure which is a function of temperature and has its limitations when it comes to monitoring present day diesel engines operating with lower air to fuel ratio. This can be explained in simple terms, if the mass of air and volume are kept constant then a 100 ◦ C change in maximum cycle temperature will change the pressure by a factor of 1.04 which is small and cannot be detected on an indicator diagram with absolute certainty. When operating closer to stoichiometric conditions, dissociation (an endothermic reaction that breaks the products back to reactants) takes place which reduces the cycle temperature. Therefore, significant changes in temperature and subsequently pressure are not observed. However, in a diesel engine cylinder with non-uniform air to fuel ratio across the cylinder the rate of combustion slows down in regions where the air-fuel mixture is rich. This influences the size of the flame and combustion period, increasing the rate of heat transfer to the combustion chanter components. It is not possible to identify such faults with the diagrams obtained from indicator instruments. 1.3. Aims and Objectives In this research, the development of a diesel engine thermal overload monitoring system is presented with applications and test results. Due to the limitation in conventional monitoring techniques for diesel engines, the requirement here is to develop a monitoring technique that can predict the air to fuel ratio within individual cylinders which will help engineers monitor the status of the engine thermal condition. 2. Diesel Engine Thermal Overload Then the hypothesis for the most probable cause of thermal overload condition on diesel engines is summarised as: (1) (2)
A low λ (excess air) ratio is the most probable cause of voluminous flame production, and there is an increase in flame size. A high surface temperature of engine component is caused by voluminous flame.
To validate the hypothesis above, experiments were undertaken to investigate the effect of λ ratio on flame size and temperature, and the effect of voluminous flame on component surface temperature. Detailed analysis of the thermal overload in diesel engines can be found in [18]. The flame visualisation test rig was manufactured using a pair of inter-connected combustion chambers. Combustion in this test rig was therefore used to replicate uniflow scavenged two stroke diesel engine combustion, with the trapped air to fuel ratio indicating conditions in the primary chamber and overall air to fuel ratio indicating condition across the combustor. During the course of initial testing with constant air flow rate and increasing levels of sub-stoichiometry it was observed that the flame lift off distance from the burner increased and the luminous flame became more voluminous. Figure 1 can be used to explain the structure of the flame at different λ. An indication that this has occurred will be an increase in exhaust temperature at the outlet probe as a results of closer proximity of the flame. The temperature at the probe increased from 775 ◦ C to 1000 ◦ C with λ changing from 1.12 to 0.71. This high temperature flame when close to or in contact with any combustion chanter component will result in an increased rate of heat transfer through the component and its consequent failure. Detailed information on the test rig development and test results analysis can be found in [18].
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Figure 1. 1. Flame position position indication. indication. Figure Figure 1. Flame position indication.
Piston crown crown temperature temperature estimation estimation was carried out on 7RTA847 engine (Sulzer, Winterthur, Piston wascarried carriedout outon onaaa7RTA847 7RTA847engine engine(Sulzer, (Sulzer,Winterthur, Winterthur, Piston crown temperature estimation was Switzerland) where wherehigh highrates rates of of hot hot corrosion corrosionwere wereevident evidenton onaa unit unit and and also also on on aa unit unit where where piston piston Switzerland) Switzerland) where highnormal. rates of Figure hot corrosion were evident on a unit and also on asurface unit where piston crown wear rates were 2a shows the thermal paint applied to the of the piston crownwear wearrates rateswere werenormal. normal.Figure Figure2a 2ashows showsthe thethermal thermalpaint paintapplied appliedto tothe thesurface surfaceof ofthe thepiston piston crown crown prior to the trial. Figure 2b shows the color shades on completion of the trial on the piston crownprior priorto tothe the trial. trial. Figure Figure2b 2bshows showsthe thecolor colorshades shadeson oncompletion completionof ofthe thetrial trialon onthe thepiston piston crown crown with the highest wear rate, which is very close to Matt Glaze and the surface temperatures crownwith withthe the highestwear wearrate, rate, whichisisvery veryclose closeto to Matt Glaze Glaze and and the the surface surface temperatures temperatures crown around the the hot hot highest zone, are are probably probablywhich much in in excess excess of of the theMatt design temperature. temperature. A comparison comparison of of the the around zone, much design A around the hot zone, are probably much in excess of the design temperature. A comparison of the thermal paint paint results results for for best best and and worst worst crown crown (Figure (Figure 2a,b) 2a,b) show show that that the the latter latter with with normal normal ware ware thermal thermal paint results for bestwith and yellowish worst crown (Figure 2a,b)Hot show that the latterhave withbeen normal ware rate has a dusty grey shade tinge at places. corrosion could caused by ratehas hasaadusty dustygrey greyshade shadewith withyellowish yellowish tinge places. Hot corrosion could have been caused rate tinge at at places. Hot corrosion could have caused by high crown surface temperature coupled with corrosive salt deposits which melt andbeen accelerate interby high crown surface temperature coupled with corrosive salt deposits melt and accelerate high crown surface temperature coupled with corrosive salt deposits whichwhich meltsalt and accelerate intergranular corrosion. The test results prove that high surface temperature and deposition on the inter-granular corrosion. The test results prove that high surface temperature and salt deposition on granular corrosion. The test results prove that high surface temperature and salt deposition on the crown in the heavily burned away regions could have been caused by flame and fuel impingement the crown in the heavily burned away regions could have been caused by flame and fuel impingement crown in the heavily burned away regions couldshould have been caused by flame andnot fuelcome impingement respectively. As in an ideal scenario, the flame be compact and should in contact respectively. As in an ideal scenario, the flame should be compact and should not come in contact with respectively. As in an ideal scenario, the flame should be compact and should not come in contact with the piston crown or exhaust valve [18]. the piston crown or exhaust valve [18]. with the piston crown or exhaust valve [18].
(a) (a)
(b) (b)
(c) (c)
Figure 2. View of thermal paint; (a) Before temperature estimation trial; (b) After trial with high wear Figure 2. After View of thermal paint; (a) Before estimation trial; (b) After trial with high wear rate; (c) with normal rate temperature [18]. Figure 2. Viewtrial of thermal paint;wear (a) Before temperature estimation trial; (b) After trial with high wear rate; (c) After trial with normal wear rate [18]. rate; (c) After trial with normal wear rate [18].
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3. Design of the Thermal Overload Monitoring System 3.1. System Design Introduction In our previous research, the effect of λ on flame size was observed with tests conducted on a continuous combustion test rig. The flame became voluminous for lambda values of approximately less than 1.2. For compression ignition engines with intermittent combustion, it would occur at higher lambda values but this needs to be confirmed by conducting tests on a diesel engines. As a voluminous flame would increase the surface temperature of combustion chamber components, the most accurate way to validate this would be to measure temperatures on these components for different values of lambda. For a diesel engine, with constant injection timing and expansion ratio, a high flame temperature would result in high exhaust temperature and low oxygen concentration. This gives the possibility of predicting the size of the flame based on oxygen concentration and temperature of the blow-down gas. The proposed engine thermal overload monitoring system mainly consists two types of sensors, a lambda sensor and a fast response thermocouple. The lambda sensor is used to measure the oxygen concentration in the blow down gas, and the fast response thermocouple is adopted to measure the exhaust temperature. Other sensors for example crank angle sensor etc. are adopted for analysis of the engine operation performance. Cylinder pressure sensors are also used to assist to identify faults [19]. 3.2. Calculation of Oxygen Concentration in the Blow Down Gas In the previous section it has been identified that a voluminous flame in the vicinity of combustion chamber components will result in high thermal stress and this will be dependent on the flame temperature. Meanwhile, voluminous flame produces at low oxygen concentration. Therefore, it is necessary to establish a relationship between lambda and the oxygen concentration in the blow down gas leaving the cylinder. A simple calculation is made for a steady flow constant pressure combustion chamber operating on gas oil. Stoichiometric air demand for the fuel is 14.9 kg and it combustion is assumed to be complete, the products will be CO2 , H2 O and N2 . The general combustion equation, where λ is the excess air ratio is given by: C12 H26 + 18.5λ[O2 + 3.76N2 ] = bCO2 + cH2 O + dO2 + 69.56λN2
(1)
An elemental balance of the reactants and products returns the following molar volumes of the products of combustion: b = 12; c = 13; d = 18.5 × (λ − 1). Then the oxygen concentration in the exhaust gas, ϕ can be represented by: ϕ=
d b + c + 69.56λ
(2)
18.5(λ − 1) 25 + 69.56λ
(3)
Substituting b, c, d yields: ϕ=
The data shown in Figure 3 demonstrated the oxygen concentration in the blow down gas using Equation (3). The gas exchange process in a diesel engine is a phase during which the products of combustion from a cylinder are removed and replaced with a fresh charge of at for the subsequent combustion cycle. For a four stroke engine this process takes place in two dedicated strokes while in a two stroke engine this process takes place within a few rotational crank angle degrees around bottom dead centre. The air lost during this process is insignificant, and the difference between trapped and overall air to fuel ratio is not significant. Overall air to fuel ratios for medium speed four stroke engines will be in the range of 1.8 to 2.2. As a result, the overall lambda value for the sub-stoichiometric condition of the four stroke diesel engine would be lower than 1.8, which corresponds to an oxygen concentration of lower
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than 9% from Figure 3. Thus, when the detected oxygen concentration in the exhaust gas is lower than 9%,Energies it will2017, be of 10, high 830 possibility for the engine to be operated in a thermal overload condition.5 of 13
Figure 3. Calculation results of oxygen concentration in the blow down gas. Figure 3. Calculation results of oxygen concentration in the blow down gas.
3.3. Thermal Overload Monitoring System 3.3. Thermal Overload Monitoring System 3.3.1. Pressure and Oxygen Sensors 3.3.1. Pressure and Oxygen Sensors One of the most effective ways to monitor the performance and condition of an engine is by One of the most effective ways to monitor performance and condition of anPiezoelectric engine is by analysing the pressure of the gas in the cylinder the throughout the combustion cycle [20]. analysing pressure the gaspressure in the cylinder throughout theare combustion cycle [20].with Piezoelectric pressurethe sensors that of measure change in the cylinder used in conjunction a crank pressure sensors measure in thevolume cylinder are[21]. used in measurement conjunction with a crank angle sensor tothat provide pistonpressure positionchange and cylinder data The of oxygen concentration in engine exhaust is widely used in the automotive industry on spark ignition gasoline angle sensor to provide piston position and cylinder volume data [21]. The measurement of oxygen engine for fuel regulation and is known the Lambdaindustry sensor. A sensor capable concentration in engine exhaust is commonly widely used in theasautomotive onlambda spark ignition gasoline of measuring a wide band oxygen concentration been obtained Bosch (Gerlingen, engine for fuel regulation and isofcommonly known as thehas Lambda sensor. A from lambda sensor capable of Germany) and isband capable of measuring from veryhas high lambda values down to 0.65. Its response time measuring a wide of oxygen concentration been obtained from Bosch (Gerlingen, Germany) of 5 ms makes its suitable for use as a diagnostic tool for slow and medium speed diesel engine. and is capable of measuring from very high lambda values down to 0.65. Its response time of 5 ms The wide band sensor operates intool conjunction withmedium a specialspeed control unitengine. which acts as an makes its suitable for use as a diagnostic for slow and diesel interface between the operator and the diagnostic system. This interface is an ETAS LA4acts lambda The wide band sensor operates in conjunction with a special control unit which as an meter (Stuttgart, Germany), a precision measuring instrument which permits cost effective interface between the operator and the diagnostic system. This interface is an ETAS LA4 lambda meter measurement of exhaust gases in gasoline, diesel and gas engines in conjunction with the broadband (Stuttgart, Germany), a precision measuring instrument which permits cost effective measurement of lambda sensors. The instrument uses fuel specific maps to convert the oxygen content and can display exhaust gases in gasoline, diesel and gas engines in conjunction with the broadband lambda sensors. both the current λ values and the air fuel ratio. The instrument permits the measurement of the The instrument uses fuel specific maps to convert the oxygen content and can display both the current following parameters shown in Table 1. λ values and the air fuel ratio. The instrument permits the measurement of the following parameters shown in Table 1. Table 1. Measurement range of testing instrument. Range TableParameters 1. Measurement range of testing instrument. Lambda 0.700–32.767 Range OxygenParameters concentration (%) 0–24.41 Air Lambda to fuel ratio 10.29–327.67 0.700–32.767 Oxygen concentration (%) 0–24.41 Airoftothe fuel ratio for use on a slow10.29–327.67 To check the effectiveness system speed diesel engine, a test for proof of
concept was conducted on a medium speed Ruston diesel engine in the Jones Marine Engineering laboratory. the engine running a constant rpm and load of 500 kW, three To checkWith the effectiveness of theatsystem for speed use onofa720 slow speed diesel engine, a testdifferent for proof conditions were simulated: normal, partial, and excessive fuel injections. As the engine was operating of concept was conducted on a medium speed Ruston diesel engine in the Jones Marine Engineering with a constant pressure ratio across all the cylinders, it was assumed that each of them will trap approximately the same mass of air for combustion. As the data in Figure 4 is used to present the pressure difference and verify the effectiveness of the sensing system, detailed analysis is not
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laboratory. With the engine running at a constant speed of 720 rpm and load of 500 kW, three different conditions were simulated: normal, partial, and excessive fuel injections. As the engine was operating with a constant pressure ratio across all the cylinders, it was assumed that each of them will trap approximately the same mass of air for combustion. As the data in Figure 4 is used to present Energies 2017, 10, 830 6 ofthe 13 pressure difference and verify the effectiveness of the sensing system, detailed analysis is not provided in this paper. It can be seen from 4 that where injection resulted in aresulted higher peak provided in this paper. It can be Figure seen from Figure 4 excessive that wherefuel excessive fuel injection in a pressure. Similar patterns were observed with normalwith and normal partial fuel Hence, the sensing higher peak pressure. Similar patterns were observed andinjection. partial fuel injection. Hence, system will system work satisfactorily when used to monitor speeda diesel engine. the sensing will work satisfactorily when usedatoslow monitor slow speed diesel engine.
Figure 4. Cylinder pressure for varing fuel injection conditions.
3.3.2. Fast Response Thermocouple Temperature is one of the most measured physical parameters for process control and fault diagnosis. The K-type thermocouple, nickel-chromium versus nickel-aluminium, nickel-aluminium, is the most widely used [22,23]. The standard robust thermocouples fitted on diesel The standard robust thermocouples fitted on diesel engines to monitor exhaust gas temperatures fromindividual individual cylinders as of part of continuous health monitoring, their temperatures from cylinders as part continuous health monitoring, have their have limitations limitations when it comes to critical fault diagnosis. They can be used to identify major and obvious when it comes to critical fault diagnosis. They can be used to identify major and obvious problems, such problems, such as lossthrough of compression leaking exhaust valverings or broken rings or any as loss of compression a leakingthrough exhaust avalve or broken piston or any piston associated problem associated that results in an increase in gas steady state exhaust temperature. response that resultsproblem in an increase in steady state exhaust temperature. The gas response time of aThe temperature time ofisadependent temperature is dependent onofthe properties of thecoefficient, sensor, theitsheat sensor on sensor the thermal properties thethermal sensor, the heat transfer sizetransfer and the coefficient, itsofsize theprocessing response associated time of any signal associated with it. In diesel response time anyand signal with it. Inprocessing a diesel engine, the temperature of aexhaust engine, the oftemperature exhaust coming out of dynamically. the cylinderThe is not constant and changes coming out the cylinder of is not constant and changes selection of a thermocouple dynamically. The selection of a thermocouple for a duration particularofsensing application, physical type for a particular sensing application, physicaltype condition, exposure, sensor lifetime and condition, sensor lifetime and accuracy all have to be considered. accuracy allduration have to of beexposure, considered. The use of very fine thermocouple i.e., K-type K-type of 0.025 mm inside inside a ceramic insulating insulating tube, tube, protected by a stainless steel outer tube is tested on aa high high speed speed diesel diesel engine engine operating operating at at 1500 1500 rpm. rpm. The entire assembly was shielded to minimise Radio Frequency Interference (RFI) problems and connected to an amplification amplification and and temperature temperature compensation compensation circuit. circuit. The exposed thermocouple junction has hasa atime time constant of 0.004 in a moving In practice, fabricating theseis sensors is constant of 0.004 s in as moving gas. Ingas. practice, fabricating these sensors extremely extremely difficult and time consuming due to nature the fragile nature of theinvolved. materialsFigure involved. Figure 5 difficult and time consuming due to the fragile of the materials 5 shows one shows one of these thermocouples in situ on the exhaust manifold between the cylinder and of these thermocouples in situ on the exhaust manifold between the cylinder and turbocharger. This turbocharger. Thislasted particular lasted before only a few hours failure and due to and gas the particular sensor only sensor a few hours failure duebefore to vibration thevibration blow down blow down gas temperature exceeding the maximum recommended for a thermocouple for this size, but produced useful results during this time.
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temperature exceeding the maximum recommended for a thermocouple for this size, but produced useful results Energies 2017, during 10, 830 this time. 7 of 13
Figure 5. Fast responsethermocouple thermocouple results results for gasgas temperature. Figure 5. Fast response for cylinder cylinderpressure pressureand andexhaust exhaust temperature.
It is seen that the temperature of the exhaust gas in the manifold increased sharply after the
It is seen that the temperature of the exhaust gas in the manifold increased sharply after the cylinder pressure pulse at approximately 0.05 s, adjacent to a noticeable drop in cylinder pressure cylinder pulse of at the approximately adjacent to a gas noticeable drop in cylinder pressure causedpressure by the opening exhaust valve.0.05 Thes, wave of exhaust exiting the cylinder is evidenced caused by the opening of the exhaust valve. The wave of exhaust gas exiting the cylinder is evidenced by the rapid increase in temperature, and the subsequent shape of the temperature trace is due to the by the rapid in temperature, andinto thethe subsequent of the temperature trace is due to the cooling of increase the exhaust gas as it expands manifold.shape The pressure pulse shows the combustion cooling of the exhaust gas asshows it expands into the manifold. The pressure shows the combustion and the temperature pulse the exhaust phase of the cycle. Also seenpulse at approximately 0.03 and and0.8 thes are temperature pulse shows the exhaust phase Also seen at approximately 0.03 and small but significant temperature pulses dueof tothe the cycle. exhaust exchange process for the adjacent cylinders. The tests were used to demonstrate the possibility of utilising dynamic temperature 0.8 s are small but significant temperature pulses due to the exhaust exchange process for the adjacent sensingThe faulttests diagnostics. cylinders. were used to demonstrate the possibility of utilising dynamic temperature sensing fault diagnostics. 4. Testing Results of the Thermal Overload Monitoring System
4. Testing Results of the Thermal Overload Monitoring System 4.1. Test Engine Description
4.1. Test A Engine Description medium speed Ruston diesel engine was instrumented to measure the required engine process parameters. carried outwas using a cylinder pressure sensorthe andrequired oxygen sensor A medium speed Testing Ruston was diesel engine instrumented to measure enginefitted process to cylinder 3. The configurations for the selected engine are listed in Table 2. parameters. Testing was carried out using a cylinder pressure sensor and oxygen sensor fitted to
cylinder 3. The configurations for the selected engine are listed in Table 2.
Table 2. Configurations for the selcted Ruston diesel engine.
Table 2. Configurations diesel engine. Engine Marker/Modelfor the selcted Ruston Ruston 6AP3 Operating cycle
Four stroke
Engine Marker/Model
Ruston 6AP3
Operating cycle
Four stroke 1000 750 203 1000 203 273 273 12.2:1 12.2:1 Pulse Pulse
Rated power (kW)
Rated (rpm) Ratedspeed power (kW) Borespeed (mm) (rpm) Rated Bore (mm) Stroke (mm) Stroke (mm) Compression ratio Compression ratio Turbocharging system Turbocharging system
750
It was expected to identify an engine thermal overload condition the novel monitoring It was expected to identify an engine thermal overload condition withwith the novel monitoring system. system. A fast response thermocouple and exhaust valve timing proximity sensors are fitted. The A fast response thermocouple and exhaust valve timing proximity sensors are fitted. The pressure pressure sensor used is a Bosch LSU 4.9 mounted on the exhaust duct between the cylinder head and
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sensor used is a Bosch LSU 4.9 mounted on the exhaust duct between the cylinder head and the common manifold. Two markers, for the start of fuel injection and the piston at top dead centre Energies 2017, 10, 830 8 of 13 (TDC) for Cylinder 3, are installed on the flywheel and a proximity sensor mounted to provide the indication. and oxygen concentration dataand is acquired aidcentre of a data the commonCylinder manifold.pressure Two markers, for the start of fuel injection the pistonwith at topthe dead (TDC) for Cylinder 3, are installed on Corporation, the flywheel and a proximity sensor mounted topost-processing provide the acquisition card (National Instruments Austin, TX, USA) and Matlab Cylinder pressure andother oxygen concentration acquired using with the aid of aDK data DAQindication. (Data acquisition) code. All monitored data data was isrecorded a Doctor 2 data acquisition card (National Instruments Corporation, Austin, TX, USA) and Matlab post-processing acquisition system developed by Icon Research (West Lothian, UK). DAQ (Data acquisition) code. All other monitored data was recorded using a Doctor DK 2 data
acquisition systemSensing developed by Icon (West Lothian, UK). 4.2. Thermal Overload System Set Research up
Three set ofOverload sensorsSensing were fitted onSet the 4.2. Thermal System upcylinder, a proximity sensor was used to measure exhaust valve timing, a lambda sensor and a fast response thermocouple to measure the oxygen concentration Three set of sensors were fitted on the cylinder, a proximity sensor was used to measure exhaust and the temperature of thesensor gas leaving theresponse cylinderthermocouple respectively.toThe oxygen profile and valve timing, a lambda and a fast measure theconcentration oxygen concentration the dynamic exhaust gas temperature, recorded with respect to the crank angle during the blow-down and the temperature of the gas leaving the cylinder respectively. The oxygen concentration profile and scavenging process, will an indication of with the thermal combustion quality and gas and the dynamic exhaust gasgive temperature, recorded respect toload, the crank angle during the blowexchange for the cylinder. Digital sensors wereofmounted onload, a bracket close to flywheel downprocess and scavenging process, will give an indication the thermal combustion quality and and gas exchange process for the TDC cylinder. Digitaland sensors were mounted on a bracket close to flywheel adjusted to measure the piston position operation speed. Although not an integral part of and adjusted to measure the piston TDC position and operation speed. Although not an integral part the proposed monitoring system, the cylinder pressure was recorded to establish a co-relation between of the proposed monitoring system, the cylinder was recordedTapping to establish co-relation the trapped lambda values and rate of pressure rise pressure due to combustion. werea fitted upstream between the trapped lambda values and rate of pressure rise due to combustion. Tapping were fitted and downstream of the turbocharger turbine to measure pressure at inlet and outlet for performance upstream and downstream of the turbocharger turbine to measure pressure at inlet and outlet for and air flow calculations. performance and air flow calculations.
4.3. Initial Test Results and Discussion
4.3. Initial Test Results and Discussion
It has discussed that overloadis is most probably caused It been has been discussed thatthe thediesel diesel engine engine thermal thermal overload most probably caused by by sub-stoichiometric conditions chamber. sub-stoichiometric conditions sub-stoichiometric conditionsininthe the combustion combustion chamber. TheThe sub-stoichiometric conditions can be can be achieved keepingthe the flow constant increasing the fuel flow or vice achievedby byeither either keeping airair flow raterate constant whichwhich increasing the fuel flow rate or vicerate versa. thethe testing, the the air flow rate is kept and theand fuelthe injection amount isamount increaseistoincrease reach to versa.During During testing, air flow rate isconstant, kept constant, fuel injection condition. Results from the the measurements taken on the engine at at reachthe thesub-stoichiometric sub-stoichiometric condition. Results from measurements taken on selected the selected engine constant load and variable fuel delivery i.e., normal and excessive injection are shown in Figures 6–8. constant load and variable fuel delivery i.e., normal and excessive injection are shown in Figures 6–8. The exhaust valve open/close signals are set the same for both injection conditions, and the other The exhaust valve open/close signals are set the same for both injection conditions, and the other operation parameters except for the fuel injection amount are remained unchanged during the operation parameters except for the fuel injection amount are remained unchanged during the testing. testing.
Figure 6. Exhaustvalve valvetiming timing for for different conditions. Figure 6. Exhaust differentinjection injection conditions.
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The oxygen concentration leaving the cylinder cylinderis seento fluctuate The oxygen concentrationin inthe theexhaust exhaust gas gas leaving leaving the the cylinder isisseen seen totofluctuate fluctuate inin The oxygen concentration in the exhaust gas in aa a symmetrical signal with a constant deviation, which is demonstrated in Figure 7. This is indicative symmetrical signal signal with with aa constant constant deviation, deviation, which which is is demonstrated demonstrated in in Figure Figure 7. 7. This This is is indicative indicative of of symmetrical of aa reduction reduction inthe thetrapped trappedair air fuel ratio due to excessive injection and the fluctuating reduction in in the trapped air fuel ratio due to excessive excessive fuelfuel injection and the the fluctuating fluctuating signalsignal is aa fuel ratio due to fuel injection and signal is consequence ofofpulse pulse type turbocharging. If If the oxygen concentration percentage drops below is aconsequence consequenceof pulsetype typeturbocharging. turbocharging. theoxygen oxygenconcentration concentration percentage drops below If the percentage drops below aa a particular value of 9%, 9%, then the engine test engine engine is of ofrisk high risk to be be operated operated at thermal thermal overload particular value of the test is high to at particular value of 9%, thenthen the test is of high torisk be operated at thermal overloadoverload condition, condition, whichinduce will further further induce to fatigue fatigue problem of the the cylinder component. component. From the test test condition, which will induce to problem of cylinder From the which will further to fatigue problem of the cylinder component. From the test results, it is results, is oxygen found that that the oxygen oxygenfor concentration for excessive excessive injection is obvious obvious lower thatinjection, of the the results, is found the concentration for injection is lower that of found thatititthe concentration excessive injection is obvious lower that of the normal normal injection, which will willof ofthermal high possibility possibility of operation. thermal overload overload operation. operation. normal which of high of thermal which willinjection, of high possibility overload
Figure 7.Oxygen Oxygenconcentration concentration for for different different injection injection conditions. Figure Oxygen concentration Figure 7.7. different injectionconditions. conditions.
As demonstrated demonstrated in Figure Figure 8, 8, the the use use of of aa fast fast response response thermocouple thermocouple gives greater greater insight insight into into AsAs demonstrated ininFigure 8, the use of a fast response thermocouplegives gives greater insight into the gas gas exchange exchange process process and and assists assists in in predicting predicting the the quality quality of of combustion. combustion. the the gas exchange process and assists in predicting the quality of combustion.
Figure 8.Exhaust Exhaustgas gastemperature temperature for for different different injection injection conditions. Figure Exhaust gas temperature Figure 8.8. different injectionconditions. conditions.
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IfIfthe tofuel fuelratio ratioisisclose close stoichiometric conditions, burning due the the trapped trapped air to to to stoichiometric conditions, slowslow burning due to theto nonnon-availability of sufficient reactive species (local conditions) will result in a high exhaust gas availability of sufficient reactive species (local conditions) will result in a high exhaust gas temperature. marginal deviation deviation in in temperature temperature temperature.However, However,the thefast fastresponse response thermocouple thermocouple shows a marginal over However,ititdoes does overaacycle cyclebut butits itstime timeresponse responseisisnot notfast fast enough enough for for medium medium speed engines. engines. However, indicatethat thatthe thedeviation deviationin inexhaust exhaust temperature temperature due to excessive injection indicate injection can can be be detected detectedwith withaa standardthermocouple. thermocouple. A appropriately thermocouple can diagnose an thermal engine overload thermal standard A appropriately sizedsized thermocouple can diagnose an engine overload condition operating by condition by observing a sharp rate of temperature at of thethe start the gas operating observing a sharp rate of temperature rise at therise start gasofexchange exchange process (blow down) indicating a much higher temperature competed to the mean exhaust process (blow down) indicating a much higher temperature competed to the mean exhaust temperature temperature (shown in Figureif 4). Similarly, thereair is loss of fresh air towards the end of the gas (shown in Figure 4). Similarly, there is loss ofif fresh towards the end of the gas exchange process exchange process (scavenging),will thecome thermocouple will come in contact with low temperature air (scavenging), the thermocouple in contact with low temperature air which will be indicated which will be indicated by a sharp reduction in temperature. The amplitude of this cyclic variation by a sharp reduction in temperature. The amplitude of this cyclic variation in temperature may be in temperature may be regarded as an indicator combustion airscavenging, being lost atwhich the end of scavenging, regarded as an indicator of combustion air being of lost at the end of results in a lower which results in a ratio. lower trapped air to fuel ratio. trapped air to fuel InfluenceofofEngine EngineThermal ThermalOverload Overload 5.5.Influence
5.1. 5.1.Test TestEngine EngineConfiguration Configuration The engine having having high high piston piston Thetests testswere werecarried carried out out on on four four cylinders cylinders of a Sulzer 7RTA84T engine crown 80% of of maximum maximumcontinuous continuous crownburn burnrates. rates.Power Powerdeveloped developed by by the the engine engine during the test was 80% rating obtained and andwere werefound foundtotobe berepeatable. repeatable. rating(27,160 (27,160kW). kW).AAlarge largenumber number of of measurements were obtained Asscavenging scavengingair airflow flowthrough througheach each cylinder cylinder is is different different the oxygen concentration As concentration values valuesused usedto to predictthe thetrapped trappedlambda lambdaare aretaken takenas as the the minimum minimum value observed during predict during the theprocess. process.Tests Testswere were carriedout outatataalater laterstage stagewith withan an additional additional sensor, a fast response thermocouple, carried thermocouple, to toinvestigate investigatethe the correlationbetween betweengas gastemperature temperatureand andoxygen oxygenin in the the exhaust exhaust gas. This was correlation was carried carriedout outon ontwo twoship ship engines,Ship ShipAAand andB, B,which which had had the the engine engine piston crown engines, crown wear wear rates rates as as shown shownbelow belowininFigure Figure9.9. Thewear wearrate ratemeasurement measurementcan canbe befound foundin inelsewhere elsewhere [24]. [24]. The
Figure9.9. Piston Piston crown crown wear wear rate rate (Ship (Ship A A and Figure and Ship Ship B). B).
5.2.Test TestResults Resultsand andAnalysis Analysis 5.2. Figures 10 10 and and 11 11 show show that that the the correlation correlation between between exhaust exhaust temperature Figures temperature and and oxygen oxygen concentration (except oxygen concentration of Cylinder 1 due to failed sensor), it can be established concentration (except oxygen concentration of Cylinder 1 due to failed sensor), it can be established that a oxygen lower oxygen concentration in the blow gas corresponds a higher gas a that lower concentration in the blow down gasdown corresponds to a highertoexhaust gas exhaust temperature. temperature. The lowest cyclic variation and lowest peak exhaust temperature suggests there is The lowest cyclic variation and lowest peak exhaust temperature suggests there is minimal or no minimal or no combustion air loss at the end of the scavenging process, which results in a high combustion air loss at the end of the scavenging process, which results in a high trapped air to fuel
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ratio as in the case Cylinder 1. The temperature of Cylinder 1 is lowest, and shows lowest trapped air to fuelofratio as in the caseexhaust of Cylinder 1. The exhaust temperature of Cylinder 1 is lowest, trapped airlowest to fuel ratio as in thewear case rate. of Cylinder 1. The exhaust temperature of Cylinder 1 is lowest, piston crown wear rate. and shows piston crown and shows lowest piston crown wear rate.
Ship A Ship A
Ship B Ship B
Figure 10. Temperature of blow down gas. Figure 10. Temperature of blow down gas. Figure 10. Temperature of blow down gas.
From the data shown in Figure 11, the oxygen concentration in Cylinder 4 is lowest (nearly 6%), From thethe data shown ininFigure concentration in Cylinder Cylinder (nearly 6%), From data shown Figure 11,the theoxygen oxygen concentration in 44isislowest (nearly 6%), and the exhaust gas temperature is11, highest. According to the analysis presented inlowest Section 3, when andthe the exhaust gas temperature is highest. According to the analysis presented in Section 3, when the anddetected the exhaust gas concentration temperature isinhighest. According the analysis in high Section 3, when oxygen the exhaust gas is to lower than 9%,presented it will be of possibility detected oxygen concentration theinexhaust gas condition. is lower than it will be of high possibility thethe detected concentration theoverload exhaust gas is lower 9%, it will be ofcrown high possibility for engineoxygen to be operated atinthermal Asthan a9%, result, the piston wear ratefor for the engine to be operated at thermal overload condition. As a result, the piston crown wearfrom rateof theof engine to be operated at thermal overload condition. As a result, the piston crown wear rate Cylinder 4 is much higher than that of the other cylinder, due to the high rate of heat transfer of Cylinder 4 is much higher than that of the other cylinder, due to the high rate of heat transfer from Cylinder 4 is much higher than that of the other cylinder, due to the high rate of heat transfer a a voluminous flame. a voluminous flame. voluminous flame.
Figure 11. Oxygen concentration in blow down gas. Figure 11.Oxygen Oxygenconcentration concentration in in blow blow down Figure 11. down gas. gas.
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6. Conclusions In this research, the development of a diesel engine thermal overload monitoring system is presented with application and test results. The designed diesel engine thermal overload monitoring system mainly consists two set of sensors, i.e., a lambda sensor to measure the oxygen concentration and a fast response thermocouple to measure the temperature of the gas leaving the cylinder. From the calculation of oxygen concentration in the blow down gas, it is suggested that if the oxygen concentration percentage drops below a particular value of 9%, then the test engine is of high risk to be operated at thermal overload condition, which will further induce to fatigue problem of the cylinder component. A medium speed Ruston diesel engine is instrumented to measure the required engine process parameters. Measurements are taken on the selected engine at constant load and variable fuel delivery i.e., normal and excessive injection. From the test results, it is found that the oxygen concentration for excessive injection is obvious lower that of the normal injection, which will of high possibility of thermal overload operation. With the application of the designed diesel engine thermal overload prediction system, it is able to help monitor the engine thermal conditions. Tests were carried out on four cylinders of a Sulzer 7RTA84T engine having high piston crown burn rates to explore the influence of engine operating at thermal overload condition. It is established that a lower oxygen concentration in the blow down gas corresponds to a higher exhaust gas temperature. The oxygen concentration in Cylinder 4 is lowest (nearly 6%), and the exhaust gas temperature is highest. As a result, the piston crown wear rate of Cylinder 4 is much higher than that of the other cylinder, due to the high rate of heat transfer from a voluminous flame. Acknowledgments: This work was funded using the EPSRC (Engineering and Physical Sciences Research Council) Impact Acceleration Account EP/K503885/1. Data supporting this publication is openly available under an Open Data Commons Open Database License. Additional metadata are available at: http://dx.doi.org/10.17634/ 123306-3. Please contact Newcastle Research Data Service at
[email protected] for access instructions. Author Contributions: Sangram Kishore Nanda and Anthony Paul Roskilly conceived and designed the experiments; Sangram Kishore Nanda performed the experiments; Boru Jia and Sangram Kishore Nanda analyzed the data and wrote the paper; Andrew Smallbone revised the manuscript. Conflicts of Interest: The authors declare no conflict of interest.
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