**4.2. Experimental method**

Determining ceramic coating effects on performance and exhaust emissions of turbocharger diesel engine requires standard values for performance indicators. For this purpose, test engine was operated without ceramic coatings according to 1231 numbered Turkish Standards (TS) experimental essentials and results were recorded. Ceramic coatings were applied after those standard tests. Cylinder heads, piston tops and intake exhaust valves were machined at 0.5 mm depth. Machining was done for achieving same compression rate with conventional combustion chamber after ceramic coating. Ceramic coating was applied by plasma spray coating system in Metal & Seramik Kaplama Ltd. Sti. in Turkey.

The most critical coated engine part is pistons due to its thermal expansion rate which is very different from selected ceramic material. In literature, ZrO2 stabilized with Y2O3 and Si3N4 ceramic coating materials are told as positive result giving materials. At cylinder heads and intake exhaust valves, ZrO2 stabilized with MgO can be utilized safely. Another important point in ceramic coatings is the binding layer composition. Coating durability is increased when NiCrAlY is used as binding layer.

Surfaces to be coated were cleaned from lubricants and other unwanted dirt after machining before roughed by sandblasting and prepared for ceramic coating. When surface preparation was done, surface was first coated with binding layer at 0.15mm thickness and then coated with 0.35 mm thick ceramic material layer. Reduction of thermal instability (high heat conduction difference) between coating layer and target surface is aimed by this way. Hence, the failure risk for coating layer is lowered. In Fig. 10, coated piston tops can be seen. Fig. 11 contains two different figures which are illustrating cylinder head and valves before coating and after coating respectively.

Ceramic materials used for coating are;


After coating process was done, coated engine parts were mounted to engine. Same circumstances with standard engine test were applied to coated engine tests. Experimental measurements were evaluated via MS Excel and Matlab v6.5 software.

In diesel engines, power output, torque and fuel consumption values according to engine speeds are named as engine characteristics. Differences in these characteristics at different load and engine speeds are illustrated with graphical curves. These curves are called as characteristic curves. Engine characteristic curves provide important information about engine performance at real time operational circumstances. Experimental measurements not always give directly the desired data. These data should be calculated using experimental measurements. Experimental measurements generally consist of torque, engine revolution rate, fuel consumption, charge air flow rate, coolant flow rate, ambient temperature, pressure and humidity, exhaust gases temperatures, coolant entrance and exit temperatures. The most important performance characteristics calculated from these measurements are effective power, torque, mean effective pressure and specific fuel consumption (Ciniviz, 2005).

Fig. 10. Ceramic coated piston tops

210 Ceramic Coatings – Applications in Engineering

1 0C accuracy thermometer which have 130 0C gauge and Precision branded barometer which has measurement range of 710-800 mmHg were used during experiments. A chronometer with 0.01 second resolution was employed while fuel consumption rate was

Determining ceramic coating effects on performance and exhaust emissions of turbocharger diesel engine requires standard values for performance indicators. For this purpose, test engine was operated without ceramic coatings according to 1231 numbered Turkish Standards (TS) experimental essentials and results were recorded. Ceramic coatings were applied after those standard tests. Cylinder heads, piston tops and intake exhaust valves were machined at 0.5 mm depth. Machining was done for achieving same compression rate with conventional combustion chamber after ceramic coating. Ceramic coating was applied

The most critical coated engine part is pistons due to its thermal expansion rate which is very different from selected ceramic material. In literature, ZrO2 stabilized with Y2O3 and Si3N4 ceramic coating materials are told as positive result giving materials. At cylinder heads and intake exhaust valves, ZrO2 stabilized with MgO can be utilized safely. Another important point in ceramic coatings is the binding layer composition. Coating durability is

Surfaces to be coated were cleaned from lubricants and other unwanted dirt after machining before roughed by sandblasting and prepared for ceramic coating. When surface preparation was done, surface was first coated with binding layer at 0.15mm thickness and then coated with 0.35 mm thick ceramic material layer. Reduction of thermal instability (high heat conduction difference) between coating layer and target surface is aimed by this way. Hence, the failure risk for coating layer is lowered. In Fig. 10, coated piston tops can be seen. Fig. 11 contains two different figures which are illustrating cylinder head and valves



After coating process was done, coated engine parts were mounted to engine. Same circumstances with standard engine test were applied to coated engine tests. Experimental

material + 0.15 mm thick NiCrAl + 0.35 mm thick Y2O3 – ZrO2.

measurements were evaluated via MS Excel and Matlab v6.5 software.

by plasma spray coating system in Metal & Seramik Kaplama Ltd. Sti. in Turkey.

**Measured parameter Measurement range Accuracy**  *k* factor 0-10 (m-1) ±0.01 Smoke intensity 0-99 (%) ±0.01 Engine revolution 0-9999 rev/min 1 rev/min

Table 5. OVLT-2600 measurement ranges and accuracies

increased when NiCrAlY is used as binding layer.

before coating and after coating respectively.

Ceramic materials used for coating are;

0.35 Y2O3 – ZrO2.

measuring.

**4.2. Experimental method** 

a) Cylinder heads and valves without coating b) Ceramic coated cylinder heads and valves Fig. 11. Cylinder head and valves before coating and after coating

During experiments, intake and exhaust valve adjustments were made according to engine catalogue values and injectors were tested at 200 bar injection pressure. Piston rings were renewed. To measure exhaust gas composition, exhaust pipe was drilled after one meter distance from exhaust pipe entrance and measurement probe was fitted to the hole. Experiments were conducted at ten different engine speeds changing between 1100 rev/min and 2800 rev/min and seven different brake loads changing between 40 Nm and full load.

Ceramic Coating Applications and Research Fields for Internal Combustion Engines 213

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

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

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

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

consumption is 220 g/kWh while SKM1 has 210 g/kWh and SKM2 has 200 g/kWh.

declining trend for ceramic coated engine.

strong.

configuration

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

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 provided in four different regions. These regions are;


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 acquired.

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