According to a poster on Quora.com: Why do steam locomotives have funnels?@Anyone Are the big inverted cone funnels spark arrestors, or for some other purpose?
I've only ever seen them on American steam locomotives.
Thanks for that information, Edd.According to a poster on Quora.com: Why do steam locomotives have funnels?
"What we Americans call the stack, the British call the chimney, which is more descriptive of it’s function. Hot gases rise, and if channeled in a vertical tube, can create a strong draft, sucking in air at the bottom. Factories, power plants and steamships can have tall chimneys, but railroad locomotives have clearance issues which limit the height, generally to around 15’. So they make the stack as tall as possible and still clear overhead structures.
Now to answer your question, the stack’s function is to create a draft through the firebox to promote combustion. If by “funnel” you mean the shape of the stack, early locomotives burned wood, which gave off sparks which were a major hazard, igniting fires in the surrounding countryside and passengers’ clothing. To try to trap the sparks, many different shapes were patented, with different combinations and arrangements of internal screens and baffles. After the civil war railroads transitioned to burning coal, with less (but not zero) sparks, and the elaborate diamond, funnel and cabbage shaped stacks were replaced by simpler straight stacks.
A final note on the induced draft. A very early breakthrough that made railroad locomotives practical was to direct the exhaust steam from the cylinders up the stack, drawing the gasses from the firebox with it. This dramatically increased the rate of combustion and hence the power generated. Compared to stationary or ship borne engines, locomotives sought to maximize power within size and weight limits and were willing to pay the expense of lower efficiency."