Regarding this picture of a Pittsburgh & Lake Erie (NYC) 2-8-4: Could anyone tell me what the canister-like objects on the side of the firebox are? I've never seen anything like this on any other steamers. Did any other locos have these?



mckay1995@comcast.net

Would they be injection molding sprues?

They are called overfire jets, a device to introduce air over the fire to promote combustion and reduce smoke.


captbuck@comcast.net

If you ever closely watch coal as it burns you will see that as it heats up it swells up and gasses are driven off. These gasses are volatiles and will burn as a gas. The problem is that with most locomotives most of the air comes in from underneath. This is what we call primary air and this air supplies the bulk of the air required for the process of combustion.

As boilers and combustion were studied it was determined that these volatile gasses can and will burn adding more heat content, reducing smoke, and increasing overall efficiency. Depending upon the boiler configuration over-fire (sometimes called secondary) air is added to provide the required oxygen to allow the volatiles to burn more completely.

Over-fire air serves two important; it provides oxygen required to burn the volatile gasses completely and it also provides turbulence to allow for thorough mixing of these volatile gasses and the air. In firebox design it is always important to consider the three “Ts” of good combustion; time, temperature, and turbulence.

Just to add to a tad bit more info, the method of adding the overfire air came in two varieties. There is the type shown in the photo where steam jets act to force air in while the other method is to simply to let the front end draught pull secondary air in through tubes that run through the water legs over the fire. The steam jets were more popular with most lines as they are very effective buy also loud and not self regulating.

Roger

> If you ever closely watch coal as it burns
> you will see that as it heats up it swells
> up and gasses are driven off. These gasses
> are volatiles and will burn as a gas. The
> problem is that with most locomotives most
> of the air comes in from underneath. This is
> what we call primary air and this air
> supplies the bulk of the air required for
> the process of combustion.

> As boilers and combustion were studied it
> was determined that these volatile gasses
> can and will burn adding more heat content,
> reducing smoke, and increasing overall
> efficiency. Depending upon the boiler
> configuration over-fire (sometimes called
> secondary) air is added to provide the
> required oxygen to allow the volatiles to
> burn more completely.

> Over-fire air serves two important; it
> provides oxygen required to burn the
> volatile gasses completely and it also
> provides turbulence to allow for thorough
> mixing of these volatile gasses and the air.
> In firebox design it is always important to
> consider the three “Ts” of good combustion;
> time, temperature, and turbulence.


belpaire@aol.com