Repository - Scientific Journals of the Maritime University of Szczecin - Effect of elevated coolant temperature...

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Maritime University of Szczecin

Akademia Morska w Szczecinie

2011, 28(100) z. 1 pp. 67–72 2011, 28(100) z. 1 s. 67–72

Effect of elevated coolant temperature on the useful

parameters of piston internal-combustion engine

Wpływ podwyższonej temperatury płynu chłodzącego

na parametry użyteczne silnika

Rafał Krakowski

Gdynia Maritime University, Mechanical Faculty Akademia Morska w Gdyni, Wydział Mechaniczny

81-225 Gdynia, ul. Morska 83, e-mail: r.krakowski@am.gdynia.pl

Key words: internal-combustion engines, cooling system, efficiency, experimental research, engine

charac-teristics

Abstract

The paper presents the characteristics to determine the effect of elevated temperature coolant in the cooling system on engine useful parameters, the torque, power, specific fuel consumption and efficiency as a function of the effective engine speed and specific fuel consumption, hourly fuel consumption and air consumption as a function of engine load. The most popular and widely used method of cooling is liquid cooling, which ensures uniformity of temperature around the combustion chamber and easy acquisition and transfer of heat, although the properties of water are limited to a maximum temperature of the coolant. Increase the efficiency of modern internal combustion piston engines is done by modern control systems units of each engine according to its operating conditions, reducing heat loss in engine cooling and recovering energy from exhaust gases (e.g.: turbine air compressors). The results of tests confirmed the benefits of increased coolant temperature. The set of characteristics that applies the pressure of the cooling system affect the fuel consumption, especially at high speed, which contributes to increase effective efficiency of the engine.

Słowa kluczowe: silniki spalinowe, chłodzenie silników, sprawność, badania eksperymentalne,

charaktery-styki silnika

Abstrakt

W artykule przedstawiono charakterystyki mające na celu określenie wpływu podwyższonej temperatury pły-nu chłodzącego w układzie chłodzenia na parametry użyteczne silnika, czyli moment obrotowy, moc, jed-nostkowe zużycie paliwa i sprawność efektywną w funkcji prędkości obrotowej silnika, a także jedjed-nostkowe i godzinowe zużycie paliwa oraz godzinowe zużycie powietrza w funkcji obciążenia silnika. Najpopularniej-szym i masowo stosowanym sposobem chłodzenia jest chłodzenie cieczowe, które zapewnia równomierność temperatury wokół komory spalania oraz łatwość przejmowania i przenoszenia ciepła, aczkolwiek właściwo-ściami wody ograniczona jest maksymalna temperatura chłodziwa. Wzrost sprawności współczesnych tłoko-wych silników spalinotłoko-wych odbywa się poprzez nowoczesne systemy sterowania poszczególnymi zespołami silnika odpowiednio do warunków pracy silnika, zmniejszenie strat energii cieplnej na chłodzenie silnika oraz odzyskiwanie energii ze spalinami (np. turbiny sprężarek powietrza). Wyniki badań potwierdziły korzyści wynikające ze zwiększenia temperatury cieczy chłodzącej. Z przedstawionych charakterystyk wynika, że za-stosowanie ciśnieniowego układu chłodzenia wpływa na mniejsze zużycie paliwa, szczególnie przy dużej prędkości obrotowej, co przyczynia się do wzrostu sprawności efektywnej silnika.

Introduction

Effective management of energy and low level of toxic emission are associate to energy conver-sion, and are the most important challenges of

to-day’s civilization. Evolution of civilization, as well as conditions of peoples’ life depend on sources of energy and effective exploitation. It includes energy used for propulsion of wheeled vehicles which are the fundamental means of transport in urban areas.

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These vehicles are still propelled by internal com-bustion engines. Comcom-bustion engines are the most common form of engine as a prime mover also. New models of the internal combustion engines being improved, first of all for increasing their effi-ciency and decreasing toxic emission and noise. This is achieved mainly by more perfect control systems.

A liquid cooling is the most popular and widely used way of cooling, which ensures more uniformi-ty temperature distribution around the combustion chamber and facilitates the acquisition and transfer of heat in comparison with direct air-cooled en-gines. Currently used liquid cooling systems using liquid-containing aqueous solutions, although the physical properties of water reduce the maximum temperature of the coolant [1].

Only a part of the energy received during burn-ing of fuel in the piston internal-combustion en-gines is converted into useful work (Fig. 1). The energy which isn’t exchanged for the useful work, is dissipated to the atmosphere by the hot exhaust gases, and discharged by the cooling system, as well as radiation out from the engine walls [2, 3].

Fig. 1. Example of the heat balance of the piston internal-combustion engine [4]

Rys. 1. Przykład bilansu ciepła tłokowego silnika spalinowego [4]

An analysis of the experiment results and litera-ture data shows that circa one third of the heat re-leased in the combustion process is transferred to the environment by the engine cooling system [5, 6, 7]. Reducing the heat discharge by the cooling sys-tem will cause an increase in the sys-temperature of the engine coolant and part of this heat can be used to increase the useful work.

Efficiency of liquid cooling systems, treated as comprehensive unit of energy management in vehicles, can be increased by controlling the electronic unit, as well as reducing the intensity of cooling the engine and thus reduce the flow of heat to the environment. The study of such a system indicate the possibility of increasing the overall efficiency and reduce the amount of toxic components in exhaust gases at low engine load, when the exhaust temperature of a classical system is too low for effective catalytic action [4, 8]. Object of research

The turbocharged Diesel engine 4CT90 680/59 was the object of research. It is a four-cylinder engine with indirect fuel injection into the vortex chamber (COMET RICARDO VB) performed in the cylinder head. 4CT90 engines are designed to drive vehicles with total weight up to 4.5 tons, and can be used as a source drive off-road vehicles, power generators and other stationary equipment. View of the engine dynamometer is shown in figure 2.

First, the engine was equipped with cooling sets including cooler with two electric independently powered fans and water pump (Fig. 2). Full and small water circulation in the system were changed by using electromagnetic valves instead the stand-ard thermostat.

The development and construction of a pressure cooling system problem is to ensure that there is no cooling system leak. A cooler is particularly sensi-tive to the pressure, therefore, a charge air cooler made of steel was used as a cooler, where all the elements are connected by welding and form a compact structure. In the model research this ex-changer fulfilled its role, whereas in the research on the real engine above a certain load there was an uncontrolled growth of both pressure and tempera-ture in the system. So finally, a shell-and-tube type heat exchanger was installed in the system.

During the tests, the engine was loaded by elec-tro rational brake Schenk W 230 with a maximum power of 230 kW. Between the brake housing and the base, the strain gauge torque meter was in-stalled, by which torque was measured. The brake was periodically calibrated using standard weights placed on saucers appearing over the load cell. The engine speed was measured using a pulse transduc-er cooptransduc-erating with a toothed rim located on the shaft brake. The air flow rate was measured using mass flow VORFLO Danfoss, acting on the basis of Karman vortices, placed in the channel inlet air to the engine. Fuel consumption measurement was performed by the volumetric flow Pierburg with

POWER

FRICTION

COOLING

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simultaneous measurement of temperature of the fuel flow, allowing the determination of fuel mass flow.

Measurements results

The speed and load characteristics with a pres-sure and a standard cooling system at a prespres-sure of 0.2 MPa (absolute pressure 0.3 MPa) during the testing dynamometer under steady state engine operating conditions was determined. Effect of rotational speed of the engine useful parameters were evaluated based on specified characteristics of the external velocity and engine load.

The speed characteristics

Waveforms of maximum torque as a function of engine speed indicates that the use of pressure cooling system and increase the engine coolant temperature up to about 118°C (Fig. 4a), reached at a pressure of about 0.2 MPa (absolute pressure of about 0.3 MPa), caused a significant increase in maximum torque over the entire range of engine speed (Fig. 3a). At a speed of 1500 rev/min and above this speed, torque increases average about 8÷10 Nm, an increase torque by about 5 to 6%. Only at low speed below 1250 rev/min torque changes were not noticeable. Simultaneously with the increase of torque and power output increased by about 3 to 5 kW (Fig. 3b).

Engine torque increase occurred at significantly lower fuel consumption (up to about 1 kg/h of top speed) with comparable fuel consumption in the

low engine speed. For this reason, a much im-proved engine economy, particularly at high engine speed above 2500 rev/min (Fig. 3c). Reduction of specific fuel consumption was approximately 20 g/kWh, an increase of about 7% in the speed range above 2500 rev/min. With the increase of coolant temperature was also effective to increase the absolute efficiency of the engine. The character-istics show that above n = 1500 rev/min is an increase in efficiency, which in the speed range of 2000÷4000 rev/min for approximately 2 to 3% (Fig. 3d).

Although the increase of engine temperature re-duces the air filling factor, the exhaust gas enthalpy increase probably causes the increase of air pres-sure in the intake duct what results with slightly larger air consumption than the standard engine. Increasing of the temperature of the fuel injection pump, causing the temperature rise of fuel and re-duce fuel consumption by dosed volume piston injection pump, although the engine power (torque) was larger.

Increase the pressure in the engine cooling sys-tem of 0.2 MPa by evaporation, caused an increase in coolant temperature of the liquid flowing from the engine to about 118C in the rotational speed above 2000 rev/min (Fig. 4a) and remained at a similar level to 4000 rev/min. Obtained in this way nearly 40 degree rise in temperature of the liquid flowing out of the engine speed range 1000÷2000 rev/min decreasing the temperature rises to about 25÷20C in the speed range 3500÷4000 rev/min. Obtaining such a temperature increase in the engine

a) b)

Fig. 2. 4CT90 engine on the dynamometer: a) the stand of the cooling system carried over from the model stand, b) stand of the cooling system after the change of the heat exchanger

Rys. 2. Silnik 4CT90 na stanowisku dynamometrycznym: a) stanowisko z układem chłodzenia przeniesionym ze stanowiska mode-lowego, b) stanowisko z układem chłodzenia po zmianie wymiennika ciepła

Shell-and-tube type heat exchanger 4CT90 engine Electrically driven water pump

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caused the need for more intensive cooling of the liquid in the radiator, making the temperature of the liquid from the cylinder block, was reduced to 60C

at 1000 rev/min and to 95C at 4000 rev/min (Fig. 4b). This temperature is only 7C to 8C higher than when using a standard cooling system.

a) b)

c) d)

Fig. 3. The speed characteristics of the engine 4CT90 with standard and pressure cooling system: a) torque, b) the power, c) specific fuel consumption, d) effective efficiency

Rys. 3. Charakterystyki prędkościowe silnika 4CT90 ze standardowym i ciśnieniowym układem chłodzenia: a) moment obrotowy, b) moc, c) jednostkowe zużycie paliwa, d) sprawność efektywna

a) b)

Fig. 4 The speed characteristics of the engine 4CT90 with standard and pressure cooling system: a) coolant temperature before radiator, b) coolant temperature before the engine block

Rys. 4. Charakterystyki prędkościowe silnika 4CT90 ze standardowym i ciśnieniowym układem chłodzenia: a) temperatura płynu chłodzącego przed chłodnicą, b) temperatura płynu chłodzącego przed blokiem silnika

100 120 140 160 180 200 1000 1500 2000 2500 3000 3500 4000 Mo [ Nm ] n [rpm]

standard cooling system pressure cooling system

0 10 20 30 40 50 60 70 1000 1500 2000 2500 3000 3500 4000 Ne [ kW ] n [rpm]

250 270 290 310 330 350 370 1000 1500 2000 2500 3000 3500 4000 ge [ g/k W h] n [rpm]

0,25 0,26 0,27 0,28 0,29 0,30 0,31 0,32 0,33 1000 1500 2000 2500 3000 3500 4000 he n [rpm] standard cooling system pressure cooling system

50 60 70 80 90 100 110 120 1000 1500 2000 2500 3000 3500 4000 T8 [ C] n [rpm]

50 60 70 80 90 100 1000 1500 2000 2500 3000 3500 4000 T0 [ C] n [rpm]

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The load characteristics

Partial engine load is very important within the scope of work, because most of the time the engine is running at light loads up to 50%. Only occasion-ally the engine develops full power. The character-istics of the engine load in the range 1500÷4000 rev/min at 500 rev/min was determined. In the zone of load between zero at about 30 Nm, up to the maximum load, results of measurement obtained from the engine were varied. The graphs missed the point the engine idling (Mo = 0) due to the fact that this is not a useful load. In the article the load char-acteristics for the speed of maximum torque motor – 2500 rev/min were presented.

The load characteristics of useful parameters of engine in comparison with standard parameters of the engine cooling system were shown in figure 5. On the load characteristics can be clearly observed reduction of hourly fuel consumption at any engine speed (Fig. 5b), reflecting the greater economic efficiency of the engine cooling system pressure. Difference in specific fuel consumption increases with increasing engine speed and reduce its load. At 1500 rev/min and 30 Nm load differential specific fuel consumption was about 30 g/kWh (reduction of about 6%), while at 4000 rev/min this difference increased to 90 g/kWh (reduction of about 12%).

When the load increases, the absolute difference in specific fuel consumption decreases by about 13 g/kWh (reduction of 4.3%) at speed of 1500 rev/min and 30 g/kWh (reduction of about 8%) at 4000 rev/min (Fig. 5a). Generally, it can be as-sumed that the specific fuel consumption is at the lower cooling system pressure by about 7%.

Reduction of specific fuel consumption is the result of reducing the hourly fuel consumption, which is also lower in the whole range of engine load in a similar proportion as the consumption unit (Fig. 5a).

Hourly air consumption also is reduced in the entire range of engine load, regardless of its speed (Fig. 5c). Air consumption is less than about 2 kg/h (decrease by 3%) at speed of 1500 rev/min to about 5 kg/h (decrease by about 1%) at 4000 rev/min. However, the greatest reduction in air consumption, because about 20 kg/h (relative decrease by 7 to 6%) had an average speed of 2500÷3000 rev/min. Conclusions

Pressure cooling system has been tested on the dynamometer running turbocharged compression ignition type 4CT90. The results show that this system ensures the maintenance of a stable coolant temperature test object over a longer period of time.

a)

b)

c)

Fig. 5. The load characteristics of the engine 4CT90 with standard and pressure cooling system at n = 2500 rev/min: a) specific fuel consumption, b) hourly fuel consumption, c) hourly air consumption

Rys. 5. Charakterystyki obciążeniowe silnika 4CT90 ze stan-dardowym i ciśnieniowym układem chłodzenia przy n = 2500 obr/min: a) jednostkowe zużycie paliwa, b) godzinowe zużycie paliwa, c) godzinowe zużycie powietrza

Controlled increase also allowed the pressure to increase the boiling point of liquid, which further increased the temperature of this liquid.

The increase in coolant temperature definitely influenced the increase in economic efficiency and increase engine maximum torque motor. On aver-age air consumption unit working on the coolant

250 300 350 400 450 500 550 20 40 60 80 100 120 140 160 180 200 ge [ g/k W h] Mo [Nm] n = 2500 [rpm]

2 4 6 8 10 12 14 16 20 40 60 80 100 120 140 160 180 200 Ge [ kg /h ] M_o [Nm] n = 2500 [rpm]

120 140 160 180 200 220 240 260 280 300 20 40 60 80 100 120 140 160 180 200 Gp [ kg /h ] M_o [Nm] n = 2500 [rpm]

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temperature at 120C is lower by about 7%, while maximum torque increased by about 5 to 6%. Cal-culated overall engine efficiency increased by about 2 to 3%.

Improving the efficiency of the engine was found for speeds above 1500 rev/min at very low speed not noticed significant changes in engine operating parameters.

Practical application of the pressure cooling sys-tem in engines requires new technologies and struc-tural solutions in electronic control of the cooling system units, in this an independently driven and controlled pump of the cooling liquid, as well as flexible materials connecting the system units re-sistant to increased temperature and pressure. References

1. WALENTYNOWICZ J., KRAKOWSKI R.: Decreasing thermal energy looses in internal combustion engines. RSM “Sys-tem Level Thermal Management for Enhanced Platform Mobility” NATO RTO AVT – 178, Bucharest 4-7.10.2010. 2. LUFT S.: Podstawy budowy silników. Warszawa, WKŁ

2006.

3. NIEWIAROWSKI K.: Tłokowe silniki spalinowe. WNT, War-szawa 1992.

4. BERNHARDT M., DOBRZYŃSKI S., LOTH E.: Silniki samo-chodowe. WKŁ, Warszawa 1988.

5. AP N.S.,MAIRE A.,JOUANNY P.,LE PRIGENT C.: Economi-cal engine cooling system. SAE TechniEconomi-cal Paper Series, 2001-01-1708.

6. OGRODZKI A.: Chłodzenie trakcyjnych silników spalino-wych. WKŁ, Warszawa 1974.

7. WALENTYNOWCZ J.: Chłodzenie tłokowych silników spali-nowych. WPT nr 12/1996.

8. KRAKOWSKI R.,WALENTYNOWICZ J.: Wpływ podwyższonej temperatury płynu chłodzącego na działanie układu chło-dzenia tłokowego silnika spalinowego. Światowy Zjazd Inżynierów Polskich, Warszawa 2010.

Others:

9. CORTONA E.,ONDER CH.H.: Engine Thermal Management with Electric Cooling Pump. SAE 2000-01-0965, Michigan 2000.

10. WALENTYNOWICZ J., KAŁDOŃSKI T., SZCZĘCH L., K AR-CZEWSKI M.,RAJEWSKI M.: Sprawozdanie końcowe reali-zacji projektu badawczego pt.: Układ chłodzenia tłokowe-go silnika spalinowetłokowe-go o podwyższonej temperaturze płynu chłodzącego. PBG 457/WAT/2001.