5121 Combustor Overiew

Scaling techniques for the design of mini combustors are less defined, due, in part, to the effects of (1) surface area/volume changes with size, (2) increased effects of wall quenching, (3) low fuel flows necessitating a small number of injectors and orifice sizing, and (4) increased effect of leakage gaps on pattern factor.

As a consequence, there is reluctance to directly apply scaling from larger combustors, and alternative design solutions have been considered, for example, by Rodgers (1974), where a single injector rotating cup fuel atomizer was successfully used to enhance cold starting with very low fuel flows.

The key combustor sizing parameter is defined as the heat release rate (HRR):

HRR = Fuel flow x LHV/(Primary volume x Pressure Ratio)

Typical HRRs for small single can combustors range from 6 to 10 million kJ/m3/bar; lower HRRs provide increased residence time and are conducive to reducing CO emissions. Relatively high HRRs can be obtained with catalytic combustors (CC), but they require the addition of some form of preburner (to 430°C) plus additional downstream volume for combustion completion. As a consequence, overall combustor volumes are similar to conventional fuel injection burners. Ultra-lean burn CCs with compressor inlet injection require expensive catalysts such as platinum or palladium.

Emissions and carbon dioxide release are rapidly becoming the dominant criteria in the design of small MTs for hybrid electric vehicles, to the point that the whole engine design may be focused upon the combustor environment and operation. The MT flowpaths shown in Figure 5.1 include a reverse flowpath focused on access and flow uniformity into a single can combustor. The preferred fuel to minimize emissions is clearly natural gas.

Solar Stirling Engine Basics Explained

Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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