**4.4 Discussion**

In this work, changes in engine performance of a four stroke direct injection four cylinder turbocharged diesel engine were investigated after it was ceramic thermal barrier coated with plasma spray coating method. For study, a specific experimental setup was utilized.

There are some significant problems between coating and coated materials due to thermal expansion ratios in aluminium-silisium alloyed pistons. To avoid these problems, 0.15 mm thick NiCrAlY was coated to base material as binding layer. Zirconia which was stabilized with yttria was used as ceramic coating material for all engine parts.

Fig. 44. *k* factor change at 200 Nm load for all engine configurations

A reduction between 4.5 to 9 percent in specific fuel consumption was achieved by ceramic coating in the study. These findings are in accordance with specific literature about ceramic coatings in diesel engines. For instance Coers et. al. (1984) reported 14%, Badgley et. al. (1990) reported 5%, Havstad et. al. (1986) reported 4-9% and Leising et. al. (1978) reported 6% specific fuel consumption reduction in thermal barrier coated engines.

Present experimental study shows that volumetric efficiency was slightly increased at low loads and engine speeds while it was increasing significantly at medium loads and engine speeds. At latter conditions, volumetric efficiency increase reached to 1-2.4%.

Ceramic coating increased exhaust gases temperatures at every operational condition. Exhaust gases temperatures were increased 150 to 200 0C according to standard engine configuration. This increase corresponds to 7 to 20 percent of standard engine exhaust gases temperatures. When a turbine is combined to the system, aforementioned excess of exhaust energy can be converted to useful mechanical energy.

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 mechanisms and low weight.

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 monoxide emission.

According to present study;

230 Ceramic Coatings – Applications in Engineering

In this work, changes in engine performance of a four stroke direct injection four cylinder turbocharged diesel engine were investigated after it was ceramic thermal barrier coated with plasma spray coating method. For study, a specific experimental setup was utilized.

There are some significant problems between coating and coated materials due to thermal expansion ratios in aluminium-silisium alloyed pistons. To avoid these problems, 0.15 mm thick NiCrAlY was coated to base material as binding layer. Zirconia which was stabilized

with yttria was used as ceramic coating material for all engine parts.

Fig. 44. *k* factor change at 200 Nm load for all engine configurations

6% specific fuel consumption reduction in thermal barrier coated engines.

speeds. At latter conditions, volumetric efficiency increase reached to 1-2.4%.

energy can be converted to useful mechanical energy.

A reduction between 4.5 to 9 percent in specific fuel consumption was achieved by ceramic coating in the study. These findings are in accordance with specific literature about ceramic coatings in diesel engines. For instance Coers et. al. (1984) reported 14%, Badgley et. al. (1990) reported 5%, Havstad et. al. (1986) reported 4-9% and Leising et. al. (1978) reported

Present experimental study shows that volumetric efficiency was slightly increased at low loads and engine speeds while it was increasing significantly at medium loads and engine

Ceramic coating increased exhaust gases temperatures at every operational condition. Exhaust gases temperatures were increased 150 to 200 0C according to standard engine configuration. This increase corresponds to 7 to 20 percent of standard engine exhaust gases temperatures. When a turbine is combined to the system, aforementioned excess of exhaust

**4.4 Discussion** 

