Re: Temperature of rocket fuel at time of blast off

Greetings:

Reference: Boeing Delta rocket web site:
http://www.boeing.com/defense- space/space/delta/delta4/delta4.htm

The difference between a jet engine and a rocket engine is that the jet
engine uses oxygen from the air for combustion with a hydrocarbon based fuel
while a rocket caries both the fuel and the oxygen supply for the combustion
process. The oxygen supply is called the oxidizer.

Early rockets typically used a common fuel such as kerosene and an acid
such as fuming nitric acid as the oxidizer. Both the fuel and the oxidizer
were kept at the ambient temperature of the local environment until they
were combined in the rocket engine to explode during the combustion process.
As larger rockets with more power for greater payloads were developed by
the Germans during World War 2, liquid oxygen was used to replace the nitric
acid as the oxidizer and kerosene remained the fuel. Liquid oxygen must be
stored in oxidizer tanks at temperatures below - 183 degrees C (- 297 degrees F)
the boiling point of oxygen. Typically the liquid oxidizer is pumped in tubes around
the bell of the rocket engine to heat the oxygen to a gaseous state and to
also cool the structure of the rocket bell at the same time.

The performance of all engines are governed by the laws of thermodynamics
which simply stated says that the greater the temperature difference between
the gasses before and after combustion, the greater will be the engines
power output. Thus using a very cold oxidizer gas with fuel at an ambient
temperature greatly increased the temperature difference of the gasses which
greatly increases the output power of the rocket engine.

Today we have rocket engines with very great power. Both the Space Shuttle
and the new Boeing Delta IV launch vehicles use liquid hydrogen as a fuel with
a boiling point of -253 degrees C (- 423 degrees F) and liquid oxygen as the
oxidizer. Each vehicle also uses two or more solid propellant boosters to
assist during the initial launch phase of the flight. While the Space Shuttle
uses two large solid propellant engines the Delta series of rockets, depending
on the payload weight, use different numbers of solid propellant rocket
engines strapped around the liquid engines. The solid propellant fuel is kept
at ambient temperature; however, it tends to be cooled by being close to the
very cold fuel and oxidizer tanks. You may recall that the Space Shuttle
Challenger disaster was caused by hot exhaust gas from the solid propellant
boosters leaking through gaskets in the solid propellant rocket motor casing
because the gaskets were to cold and they lost their flexability.

The Boeing Delta web site referenced above has pictures and drawings of the
Delta's liquid and solid rocket engine configurations. The following is quoted
from the web site:

"Delta IV Vehicle Description
The Delta IV family blends new and mature technology to launch virtually any
size medium or heavy payload into space. It is composed of five vehicles based
on a common booster core (CBC) first stage. Delta IV second stages are derived
from the Delta III second stage, using the same RL10B-2 engine, but with two
sizes of expanded fuel and oxidizer tanks, depending on the model.
In designing the five Delta IV configurations, Boeing conducted extensive
discussions with government and commercial customers concerning their present
and future launch requirements. Proven technical features and processes were
carried over from earlier Delta vehicles to Delta IV. New technologies and
processes were incorporated where they added capability or reduced cost.
RS-68 Main Engine
Delta IV uses the new Boeing Rocketdyne-built RS-68 liquid hydrogen and liquid
oxygen engine, which produces 2,891 kN (650,000 lb) of thrust. This engine is
mounted on a CBC first-stage structure, which has been designed for ease of
manufacture. Thirty percent more efficient than conventional liquid
oxygen/kerosene engines, the RS-68 is environmentally friendly, producing
only steam as a combustion by-product.

Delta IV Medium
The Delta IV Medium vehicle is built around the CBC first stage and includes
the baseline second stage derived from the Delta III, but with stretched fuel
and oxidizer tanks for increased performance. This Delta version can lift up
to 4,210 kg (9,285 lb) to geosynchronous transfer orbit (GTO). The payload is
encapsulated in a 4-m (13.1-ft) diameter fairing for protection.

Delta IV Medium-Plus
Three Delta IV Medium-Plus vehicles use the common booster core and are
augmented by either two or four solid rocket strap-on graphite-epoxy motors
(GEMs). These vehicles are designated first by the diameter in meters of the
upper stage and payload fairing and then by the number of GEMs added to the
first stage for boost assist; for example, (4,2)."


Best regards, Your Mad Scientist
Adrian Popa