PSI - Issue 60

Sarath Chandran Nair S. et al. / Procedia Structural Integrity 60 (2024) 564–574 Sarath Chandran Nair S. / Structural Integrity Procedia 00 (2023) 000 – 000

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Fig. 1. Thermal barrier coating scheme in Semi-cryogenic engine

The combustion chamber with channel milled inner shell made of copper alloy having high thermal conductivity and high strength and brazed outer shell made of high strength stainless steel to form the coolant channel passages. The ribs provided on the inner shell act as the load transfer member to the outer wall and acts as conductive fins to aid the heat transfer efficiently. Isrosene is used as the regenerative coolant, which is also used as fuel for combustion. High heat flux in the critical zone in the combustion chamber is managed by: (1) providing helically milled coolant channels, (2) providing TBC on the inner wall and (3) by employing Autonomous Film Cooling (AFC) for throat region. Dissociation of Isrosene at higher temperature results in release of carbon particles which deposits on the walls. This carbon layer acts as an insulator and local heating will takes place. Due to ineffective cooling and localised heating, inner copper wall will puncture and structural failure will occur. Thermal Barrier Coating will not allow to rise the temperature in the channels above coking temperature and prevents coking of Isrosene. The features of a thermal barrier coating are: • High melting point • High thermal shock resistance • High coefficient of thermal expansion • Low thermal conductivity • Resistance to oxidation and chemical reaction • Resistance to mechanical erosion 3. Structure of Thermal Barrier Coating in Semi-cryogenic engine Thermal Barrier coating provided in Semi-cryogenic engine consists of Nickel coating for the cylindrical segment and Autonomous Film Cooling (AFC) segments and a combination of Nickel and Milk-Chrome coating for the convergent divergent segment. The coating thickness required to be achieved on these segments as per design specification is given in table 1. The coating scheme planned for cylindrical segment, AFC segments and convergent divergent segment (Nozzle first segment) is shown in fig. 2.

Table 1. Coating thickness in Semi-cryogenic engine Region Type of coating

Coating thickness

Cylindrical segment

Nickel coating

150 µm

AFC segment

Nickel coating

150 µm

Convergent divergent segment

Nickel and Chromium coating

300 µm