There is ongoing demand for increased turbine entry temperhotter particles are more likely to deposit and hotter surfaces atures, and hence improved engine efficiency. This applies to both power generation turbines and those used for propulsion (aero and marine). Ingested particulate, such as sand, fly ash, and volcanic ash (VA), often referred to generically as calcia– magnesia–alumina–silica (CMAS), can cause significant problems in both types of turbine. Such particles may melt, or at least soften, in flight, making it more likely that they will adhere to surfaces within the turbine on impact. Increased turbine entry temperatures clearly raise the danger of this happening. Particulate CMAS from volcanoes, provided it does adhere (rather than simply passing through the engine), can be quite severely deleterious in aeroengines. Such ash can be more erosive, and have a significantly lower melting point, compared to conventional air borne dust. In the combustion chamber, where the flame temperature may be as high as 1650 °C, silica-based slag deposits have been observed to plug combustor liner cooling holes, thus creating hot spots that can lead to premature failure. Deposits can also form on blade surfaces and along nozzle guide vanes, causing local overheating. Both erosion and deposition are known to increase levels of surface roughness, which produces corresponding increases in heat transfer (up to 50%) and skin friction (up to 300%). Among the most important parameters determining the level of deposition are the gas (and particle) temperature and also the turbine surface temperature. The particle temperature at the end of its flight determines its physical state, which in turn influences whether it will cause erosion upon impact or deposition. Lower deposition levels were observed in areas with reduced turbine surface temperature. Experiments conducted by Crosby et al., using an accelerated deposition facility, showed that larger and