**4.3 Experimental results**

In Fig. 13 and Fig. 14, specific fuel consumption comparison of SKM1 and SKM2 with standard engine are provided respectively. Specific fuel consumption changing with engine speed at full load for all engine configurations are given in Fig. 15. For partial load measurement points which are 40, 120 and 200 Nm, similar specific fuel consumption comparison graphics are given for all engine configurations at Fig. 16, 17 and 18 respectively. At first region in three dimensional performance map for specific fuel

Measurement points are 1100-1200-1400-1600-1800-2000-2200-2400-2600-2800 rev/min and 40-80-120-160-200-240 Nm and full load. Due to vast number of experimental results, only

Two different ceramic coated combustion chambers were compared with standard combustion chamber. In the first one, only cylinder heads and intake exhaust valves were coated. This configuration is represented by SKM1 in graphics. In second one, piston tops also coated with selected ceramic material. So, whole combustion chamber was coated in second configuration. Second configuration is represented as SKM2 in graphics. Three dimensional performance curves obtained in experimental study were evaluated and

An example graphic layout was given in Fig. 12 for previously mentioned regions. In two dimensional graphics, results are provided for 40, 120, 200 Nm and full load points. Before experiments, engine was heated by operating low and medium loads thus steady state was

Fig. 12. Three dimensional performance map and regions for evaluation

In Fig. 13 and Fig. 14, specific fuel consumption comparison of SKM1 and SKM2 with standard engine are provided respectively. Specific fuel consumption changing with engine speed at full load for all engine configurations are given in Fig. 15. For partial load measurement points which are 40, 120 and 200 Nm, similar specific fuel consumption comparison graphics are given for all engine configurations at Fig. 16, 17 and 18 respectively. At first region in three dimensional performance map for specific fuel

40, 120, 200 Nm and full load points are presented in this study.

provided in four different regions. These regions are;

1. Low load, low speed 2. High load, low speed 3. Low load, high speed 4. High load, high speed

**4.3 Experimental results** 

acquired.

consumption, SKM1 exhibits 4.5 percent and SKM2 9 percent low specific fuel consumption comparing with standard engine. These figures indicate that there is an important decrease in specific fuel consumption by the utilisation of ceramic thermal barrier coating. This decrease presents continuity at low and medium engine torques. At high torque and high engine speeds, in the other hand, specific fuel consumption decrease continues with a declining trend for ceramic coated engine.

For specific fuel consumption rate, especially second region gives better results. At 1100- 1800 rev/min engine speed and 160-200 Nm torque range, standard engine specific fuel consumption is 220 g/kWh while SKM1 has 210 g/kWh and SKM2 has 200 g/kWh.

Fig. 19 and 20 are presented for comparing exhaust gas temperature increase in SKM1 and SKM2 with standard engine respectively. Figures are clearly indicating high exhaust temperatures in ceramic coated engines. In third region, the difference between standard engine exhaust temperatures and ceramic coated engine exhaust temperatures are relatively strong.

Fig. 13. Three dimensional specific fuel consumption map for SKM1 and standard engine configuration

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 215

Fig. 16. Specific fuel consumption rate at 40 Nm load for all engine configurations

Fig. 17. Specific fuel consumption rate at 120 Nm load for all engine configurations

Fig. 14. Three dimensional specific fuel consumption map for SKM2 and standard engine configuration

Fig. 15. Specific fuel consumption rate at full load for all engine configurations

Fig. 14. Three dimensional specific fuel consumption map for SKM2 and standard engine

Fig. 15. Specific fuel consumption rate at full load for all engine configurations

configuration

Fig. 16. Specific fuel consumption rate at 40 Nm load for all engine configurations

Fig. 17. Specific fuel consumption rate at 120 Nm load for all engine configurations

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 217

Fig. 20. Three dimensional exhaust temperatures map for SKM2 and standard engine

Fig. 21. Volumetric efficiency change at full load for all engine configurations

One can expect that ceramic thermal barrier coating may decrease volumetric efficiency due to increased in-cylinder temperatures. Although exhaust gases and cylinder wall temperatures are high enough to make such effect, turbocharger causes an opposite effect in this study. Fig. 21 illustrates volumetric efficiency change of engine configurations with engine speed at full load. In a same way, Fig. 22, 23 and 24 are presented for 40, 120 and 200

configuration

Nm brake loads respectively.

Fig. 18. Specific fuel consumption rate at 200 Nm load for all engine configurations

Fig. 19. Three dimensional exhaust temperatures map for SKM1 and standard engine configuration

Fig. 18. Specific fuel consumption rate at 200 Nm load for all engine configurations

Fig. 19. Three dimensional exhaust temperatures map for SKM1 and standard engine

configuration

Fig. 20. Three dimensional exhaust temperatures map for SKM2 and standard engine configuration

One can expect that ceramic thermal barrier coating may decrease volumetric efficiency due to increased in-cylinder temperatures. Although exhaust gases and cylinder wall temperatures are high enough to make such effect, turbocharger causes an opposite effect in this study. Fig. 21 illustrates volumetric efficiency change of engine configurations with engine speed at full load. In a same way, Fig. 22, 23 and 24 are presented for 40, 120 and 200 Nm brake loads respectively.

Fig. 21. Volumetric efficiency change at full load for all engine configurations

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 219

Fig. 24. Volumetric efficiency change at 200 Nm load for all engine configurations

Fig. 25. Engine power output change at full load for all engine configurations

Fig. 25 for engine power and in Fig. 26 for torque at full load.

Engine power output is increased between 1-3% and torque increased between 1,5-2,5% by ceramic coating comparing with standard diesel engine. These observations can be chased in

Fig. 22. Volumetric efficiency change at 40 Nm load for all engine configurations

Fig. 23. Volumetric efficiency change at 120 Nm load for all engine configurations

Fig. 22. Volumetric efficiency change at 40 Nm load for all engine configurations

Fig. 23. Volumetric efficiency change at 120 Nm load for all engine configurations

Fig. 24. Volumetric efficiency change at 200 Nm load for all engine configurations

Fig. 25. Engine power output change at full load for all engine configurations

Engine power output is increased between 1-3% and torque increased between 1,5-2,5% by ceramic coating comparing with standard diesel engine. These observations can be chased in Fig. 25 for engine power and in Fig. 26 for torque at full load.

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 221

Fig. 28. Heat transfer rate to coolant at 40 Nm load for all engine configurations

Fig. 29. Heat transfer rate to coolant at 120 Nm load for all engine configurations

Some of the heat after combustion can't be converted into mechanical energy and also it can't be transferred to coolant. This heat portion is carried with exhaust gases. Percentage rate

Fig. 26. Engine torque change at full load for all engine configurations

In Fig. 27, heat flux transferred to engine coolant changing with engine speed can be seen at full load for all engine configurations. In Fig. 28, 29 and 30, same graphic was drawn for 40, 120 and 200 Nm loads. In both coated engine configurations and standard engine, heat flux to coolant increase with increasing engine speed however its percentage to total heat is decreasing. These results are compatible with Wallace et. al. (1979; 1984). Experimental results show that heat flux was reduced at a rate of 19 percent by ceramic coating.

Fig. 27. Heat transfer rate to coolant at full load for all engine configurations

Fig. 26. Engine torque change at full load for all engine configurations

In Fig. 27, heat flux transferred to engine coolant changing with engine speed can be seen at full load for all engine configurations. In Fig. 28, 29 and 30, same graphic was drawn for 40, 120 and 200 Nm loads. In both coated engine configurations and standard engine, heat flux to coolant increase with increasing engine speed however its percentage to total heat is decreasing. These results are compatible with Wallace et. al. (1979; 1984). Experimental

results show that heat flux was reduced at a rate of 19 percent by ceramic coating.

Fig. 27. Heat transfer rate to coolant at full load for all engine configurations

Fig. 28. Heat transfer rate to coolant at 40 Nm load for all engine configurations

Fig. 29. Heat transfer rate to coolant at 120 Nm load for all engine configurations

Some of the heat after combustion can't be converted into mechanical energy and also it can't be transferred to coolant. This heat portion is carried with exhaust gases. Percentage rate

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 223

Fig. 32. Heat carried with exhaust gases at 40 Nm load for all engine configurations

Fig. 33. Heat carried with exhaust gases at 120 Nm load for all engine configurations

emissions for SKM1-standard engine and SKM2-standard engine comparisons.

One of the most dangerous exhaust emissions is nitrogen oxides in diesel engines. Nitrogen oxide emissions are generally generated over 1800 0C. Top temperature value during combustion can increase about 150-200 0C in ceramic thermal barrier coated engines. High in-cylinder temperatures cause an increase in nitrogen oxides emissions about 10% comparing with standard engine operation. Fig. 35 and 36 illustrates nitrogen oxides

increase of exhaust gas energy is inversely proportional with heat flux to coolant. According to experimental results, about 17.5% increase was observed in the heat energy that passes to exhaust gases. Exhaust heat energy changing with engine speed at full, 40 Nm, 120 Nm and 200 Nm loads for all engine configurations are given in Fig. 31, 32, 33 and 34 respectively.

Fig. 30. Heat transfer rate to coolant at 200 Nm load for all engine configurations

Fig. 31. Heat carried with exhaust gases at full load for all engine configurations

increase of exhaust gas energy is inversely proportional with heat flux to coolant. According to experimental results, about 17.5% increase was observed in the heat energy that passes to exhaust gases. Exhaust heat energy changing with engine speed at full, 40 Nm, 120 Nm and 200 Nm loads for all engine configurations are given in Fig. 31, 32, 33 and 34 respectively.

Fig. 30. Heat transfer rate to coolant at 200 Nm load for all engine configurations

Fig. 31. Heat carried with exhaust gases at full load for all engine configurations

Fig. 32. Heat carried with exhaust gases at 40 Nm load for all engine configurations

Fig. 33. Heat carried with exhaust gases at 120 Nm load for all engine configurations

One of the most dangerous exhaust emissions is nitrogen oxides in diesel engines. Nitrogen oxide emissions are generally generated over 1800 0C. Top temperature value during combustion can increase about 150-200 0C in ceramic thermal barrier coated engines. High in-cylinder temperatures cause an increase in nitrogen oxides emissions about 10% comparing with standard engine operation. Fig. 35 and 36 illustrates nitrogen oxides emissions for SKM1-standard engine and SKM2-standard engine comparisons.

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 225

Fig. 36. Three dimensional nitrogen oxides emissions map for SKM2 and standard engine

engine speed at full load, 40 Nm load, 120 Nm load and 200 Nm load respectively.

Fig. 37. Carbon monoxide change at full load for all engine configurations

In standard diesel engines, fuel air mixture ratio is changing with load condition and revolution rate of engine and usually engines are operated at lean fuel air mixture. In this situation, carbon monoxide is converted to carbon dioxide due to sufficient oxygen existence in combustion chamber. However, low combustion temperature, short combustion period and low oxygen content may lead to high carbon monoxide emissions. In ceramic coated engine configurations, carbon monoxide emissions reduced at a rate of 5 to 10% by the increased exhaust temperature. Fig. 37 to 40 show changes in carbon monoxide emissions according to

configurations

Fig. 34. Heat carried with exhaust gases at 200 Nm load for all engine configurations

Fig. 35. Three dimensional nitrogen oxides emissions map for SKM1 and standard engine configurations

Fig. 34. Heat carried with exhaust gases at 200 Nm load for all engine configurations

Fig. 35. Three dimensional nitrogen oxides emissions map for SKM1 and standard engine

configurations

Fig. 36. Three dimensional nitrogen oxides emissions map for SKM2 and standard engine configurations

In standard diesel engines, fuel air mixture ratio is changing with load condition and revolution rate of engine and usually engines are operated at lean fuel air mixture. In this situation, carbon monoxide is converted to carbon dioxide due to sufficient oxygen existence in combustion chamber. However, low combustion temperature, short combustion period and low oxygen content may lead to high carbon monoxide emissions. In ceramic coated engine configurations, carbon monoxide emissions reduced at a rate of 5 to 10% by the increased exhaust temperature. Fig. 37 to 40 show changes in carbon monoxide emissions according to engine speed at full load, 40 Nm load, 120 Nm load and 200 Nm load respectively.

Fig. 37. Carbon monoxide change at full load for all engine configurations

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 227

Fig. 40. Carbon monoxide change at 200 Nm load for all engine configurations

Fig. 41. *k* factor change at full load for all engine configurations

Fig. 38. Carbon monoxide change at 40 Nm load for all engine configurations

Smoke intensity can be evaluated by *k* factor in internal combustion engines. Since diesel engines have a smoke emission problem, the effects of ceramic thermal barrier coating to smoke emissions should be evaluated. Similarly to previous exhaust emission graphics, Fig. 41 to 44 show changes in *k* factor according to engine speed at full load, 40 Nm load, 120 Nm load and 200 Nm load respectively. When figures are investigated, it can be observed that *k* factor decreasing with increasing engine speed. This is due to improved combustion in cylinders owing to increasing temperature. Hence, ceramic coated engine configurations exhibit 18% better smoke emissions.

Fig. 39. Carbon monoxide change at 120 Nm load for all engine configurations

Fig. 38. Carbon monoxide change at 40 Nm load for all engine configurations

Fig. 39. Carbon monoxide change at 120 Nm load for all engine configurations

exhibit 18% better smoke emissions.

Smoke intensity can be evaluated by *k* factor in internal combustion engines. Since diesel engines have a smoke emission problem, the effects of ceramic thermal barrier coating to smoke emissions should be evaluated. Similarly to previous exhaust emission graphics, Fig. 41 to 44 show changes in *k* factor according to engine speed at full load, 40 Nm load, 120 Nm load and 200 Nm load respectively. When figures are investigated, it can be observed that *k* factor decreasing with increasing engine speed. This is due to improved combustion in cylinders owing to increasing temperature. Hence, ceramic coated engine configurations

Fig. 40. Carbon monoxide change at 200 Nm load for all engine configurations

Fig. 41. *k* factor change at full load for all engine configurations

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 229

Fig. 43. *k* factor change at 120 Nm load for all engine configurations

Fig. 42. *k* factor change at 40 Nm load for all engine configurations

Fig. 42. *k* factor change at 40 Nm load for all engine configurations

Fig. 43. *k* factor change at 120 Nm load for all engine configurations

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 231

Heat flux to coolant is also decreased at a rate of 19 percent in present work. This is an important result owing to the possibility of downsizing of cooling system. Reducing sizes of cooling system would be returned as low mechanical energy consume to pumping

Carbon monoxide emission was decreased 12%, and soot was decreased about 28% in present experimental work. However nitrogen oxides were increased at a rate of 20%. In thermal barrier coating literature for internal combustion engines, reduction of carbon monoxide and soot was emphasized by a lot of researchers. Sudhakar (1984), Toyama et. al. (1989), Assanis et. al. (1991), Amann (1988), Bryzik et. al. (1983) and Matsuoka et. al. (1993) are some of these researchers. Assanis et. al. (1991) reported 30-60% reduction in carbon

ZrO2 stabilized with Y2O3 over NiCrAlY binding layer as a coating material gives good

As ceramic coating material, ZrO2 stabilized with Y2O3 is expensive for practical usage.

Injection systems may be tuned for a proper operation in ceramic coated engines. Thus,

 Alternative fuels can be tested in ceramic coated engines since combustion temperature is increased. Some fuels react positively to this temperature increase as they can be

Afify, E.M. & Klett, D.E. (1996), *The Effect Of Selective Insulation On The Performance,* 

Alkidas A.C. (1989), *Performance and Emissions Achievements with an Uncooled Heavy Duty,* 

Amann, C.A. (1988), *Promises and Challenges of the Low-Heat Rejection Diesel*, Journal of

Anonymous, (2004), *Coating Methods,* Senkron Metal A.S., 02.10.2004, Available from

Assanis, D., Wiese, K., Schwarz, E. & Bryzik, W. (1991), *The Effects Of Ceramic Coatings On* 

Badgley, P., Kamo, R., Bryzik, W. & Schwarz, E. (1990), *Nato Durability Test of an Adiabatic* 

Balc, M. (1983). *Heat Release Characteristics of a Diesel Type Combustion Chamber,* Msc Thesis,

Beg, R.A., Bose, P.K., Ghosh, B.B., Banerjee, T.Kr. & Ghosh, A. Kr. (1997), *Experimental* 

*Diesel Engine Performance And Exhaust Emissions*, International & Congress and

*Investigation On Some Performance Parameters Of A Diesel Engine Using Ceramic Coating On The Top Of The Piston,* International Congress & Exposition Detroit,

*Combustion, And NO Emissions Of A DI Diesel Engine*, International & Congress and

mechanisms and low weight.

monoxide emission.

According to present study;

results for aluminium alloyed pistons.

improvements can be enhanced.

burned more efficiently.

**5. References** 

More research should be performed to reduce its cost. Cylinder walls also can be coated to reduce heat rejection.

Exposition, Detroit, Michigan February 26-29

www.senkronmetal.com.tr (in Turkish)

Exposition, Detroit, Michigan, USA

The Univesrsity of Bath, England

Michigan, February 24-27

*Truck Engine*, SAE, Paper 900621, USA

*Single Cylinder Diesel Engine*, SAE, Paper 890144, USA

Engineering for Gas Turbines and Power, Vol. 110
