Single-port air-intake

When the airflow induced from the atmosphere is introduced through the singleport intake, the mixture formed in the forward part of the ramburner is fuel-lean because all the air induced from the single-port air-intake is introduced into the forward part. Thus, an excess-air mixture (fuel-lean mixture) is formed, the temperature of which becomes too low to initiate self-ignition. However, when a multi-port intake is used, the airflow is divided into two separate flows, entering at the forward part and the rear part of the ramburner. At the upstream flow, the air-to-fuel ratio can be made stoichiometric, which allows the mixture to ignite. At the downstream flow, the excess air is mixed with the combustion products and the temperature is lowered to increase the specific impulse. 

Fig. 15.23 Effect of air mixing process in the ramburner on combustion efficiency for two single-port intakes or two multi-port intakes as a function of boron particle size.

Historically, charcoal was produced by piling wood in a cone-shaped mound and covering it with dirt, turf, or ashes, leaving air intake holes around the bottom of the pile and a chimney port at the top (Moscowitz, 1978). The wood was set afire and allowed to bum slowly then the air holes were covered so the pile would cool slowly. In more modem times, the single-use charcoal pit was replaced by a stone, brick, or concrete kiln that would hold 25-75 cords of wood (1 cord = 4 ft x 4 ft x 8 ft). A large batch might bum for 3-4 weeks and take 7-10 days to cool. 

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