Reduction of heat transfer and heat load in internalcombustion engines
Background
In a modern light duty diesel engine, about 20%of the fuel heat escapes from the combustionchamber to the coolant. This leads to loss of effi-ciency and high thermal loads on engine compo-nents. One way to reduce these heat losses andthermal loads is to apply thermal barrier coat-ings (TBC) on the combustion chamber walls.However, state of the art TBCs are not very ef-fective and need to be improved to be of use ininternal combustion engines.
Method
The approach in this project is experimental,based on cylinder pressure measurements in asingle cylinder light duty diesel engine. In thefirst experimental campaign, two typical state ofthe art TBCs; plasma sprayed zirconia and hardanodized alumina were tested. In the second ex-perimental campaign, novel coatings were eval-uated, see Figure 1.
Figure 1. Pistons with air plasma sprayed (APS)and suspension plasma sprayed (SPS) coatingsof zirconia (YSZ) and gadolinium (GZO).
A new finer coating structure and a new mate-rial were applied, created by suspension plasmaspraying and the use of gadolinium-zirconate.
The typically rough and porous coatings werepolished to reduce heat losses and one set of pis-tons was sealed with a polysilazane.
Results
High surface roughness was identified as onecause for poor TBC performance in the first ex-periments. The second experiments show poten-tial for the combination of SPS and gadolinium-zirconate as shown in Figure 2. Sealing thesurface was not effective except for SPS zirco-nia.
44.5%
45.0%
45.5%
Reference
YSZ-APS-open
YSZ-SPS-open
GZO-SPS-open
YSZ-APS-sealed
YSZ-SPS-sealed
GZO-SPS-sealed
IndicatedEffi
cien
cy[%
]
Mediumload:1500rpm,30mgfuel/str
Figure 2. Efficiency of the coated pistons com-pared to an uncoated reference piston. Error barsshow the 95% confidence intervals.
Conclusions and outlook
Small improvements were made by reductionof coating surface roughness and the use ofgadolinium-zirconate and SPS. Surface sealingwith plasma sprayed metal and dense aluminaare the subject of the next experiments.
Contact information:Joop Somhorst, +46 (0)723 [email protected]
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