Chemical Engineering Science 61 (2006) 5427 – 5439 www.elsevier.com/locate/ces 3-D modelling of kerosene-fuelled HVOF thermal spray gun S. Kamnis, S. Gu ∗ School of Engineering and Applied Science, Aston University, Aston Triangle, Birmingham B4 7ET, UK Received 9 December 2005; received in revised form 6 March 2006; accepted 4 April 2006 Available online 21 April 2006 Abstract Liquid-fuelled high-velocity oxy-fuel (HVOF) thermal spraying systems are capable of generating more momentum output to powder particles in comparison with gas-fuelled systems. The use of low-cost fuel such as kerosene makes this technology particular attractive. High- quality coating requires thermal spraying systems delivering consistent performance as a result of the combustion during HVOF spraying. The combustion of kerosene is very complicated due to the variation of fuel composition and subsequently makes it extremely challenging for process control. This paper describes a 3-D simulation using mathematical models available in a commercial finite volume CFD code. The combustion and discrete particle models within the numerical code are applied to solve the combustion of kerosene and couple the motion of fuel droplets with the gas flow dynamics in a Lagrangian fashion. The effects of liquid fuel droplets on the thermodynamics of the combusting gas flow are examined thoroughly.  2006 Elsevier Ltd. All rights reserved. Keywords: CFD; HVOF; Gas dynamics; Combustion; Kerosene 1. Introduction The technology of high-velocity oxygen fuel (HVOF) ther- mal spraying has been transforming from gas-fuelled towards liquid-fuelled systems. An apparent benefit from that devel- opment is to use low-cost fuels such as kerosene. In addi- tion, liquid-fuelled HVOF guns are normally designed with a convergent–divergent nozzle, which gives superior acceler- ation to the gas flow and high momentum output to pow- der particles. Research on coating microstructure has shown that liquid-fuelled systems generate denser coating structure and better bonding without over-melting the powder particles in comparison to gas-fuelled systems (Zhang et al., 2003). During a liquid-fuelled HVOF thermal spraying as shown in Fig. 1, premixed fuel and oxygen streams are injected into combustion chambers and energy generated by the combustion process is transformed into a hot high-pressure gas that heats and accelerates powder particles. Powder is normally fed into the hot gas stream at upstream of the nozzle instead of being ∗ Corresponding author. Tel.: +44(0)1212043582; fax: +44(0)1213335809. E-mail addresses: kamniss@aston.ac.uk (S. Kamnis), s.gu@aston.ac.uk (S. Gu). 0009-2509/$ - see front matter  2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2006.04.005 directly fed into combustion chambers, which effectively re- duces over-heating to powder particles and contributes to the unique feature of high powder impact velocity without over- heating. The overall process of HVOF thermal spraying is very complicated with combustion, supersonic flow expansion, tur- bulent mixing and gas–solid interaction. As a critical element of the process, combustion not only generates the required en- ergy for powder heating but also affects the multiphase flow pattern. An efficient combustion process is very important to deliver consistent quality performance for HVOF spraying. The combustion of liquid fuel, such as kerosene is very compli- cated, due to the large variation of composition and fuel quality. A perfectly designed liquid-fuelled HVOF system specialised for the UK market may not have the same performance in the US or other European counties. It is expected that the evapo- ration of fuel droplet would influence the combustion process, therefore, the fuel atomisation mechanism needs to be carefully controlled. To date the research on thermal spraying has progressed in both experimental and modelling fashions. Experiments have been focused heavily on microstructure characterisation and certain element of in-flight particle diagnosis. Numeri- cal modelling has become an important tool to underpin the