T-Stoff - The Oxidant 1

The basis for almost all Walter rocket motors is hydrogen peroxide. With the chemical formula of (H₂O₂) it is an oxygen rich liquid which, upon decomposition, gives out heat at a rate equivalent to gunpowder.

T-Stoff is volatile and will naturally decompose, but the Walter Werke carried out a large amount of work to establish the correct dilutions and proportions to make the substance powerful enough for a motor, stable enough to store and capable of being controlled during decomposition.

T-Stoff was generally an 80% concentrated form, diluted with water, 20% by weight. When brought into contact with a catalyst, the peroxide decomposes into a mixture of superheated steam and oxygen, at around 500^o centigrade. Fed directly to an expansion venturi, thrust will result. This basic process was used as the principle of Walter's so-called "Cold" Motors.

C-Stoff - The Fuel 1

To increase the efficiency of the motor, a fuel was injected into the mixture, utilising the oxygen released during decomposition to promote combustion.

The liquid fuel used was methyl alcohol, mixed with a compound called hydrazine hydrate. This latter was used to ensure the smooth, continuous combustion of the fuel.

The theoretical heat of this reaction would raise the temperature at the combustion chamber to over 1850^o, so the actual C-Stoff fuel used, was a dilution with water. This kept the combustion chamber to a manageable 1750^o. The difference in temperatures between this and the plain decomposition engine led to the fuelled motor being referred to as the "Hot" motor.

T-Stoff - In Detail 2

Hydrogen Peroxide	H2O2	80% by Weight
Water	H2O	20% by Weight
Stabilisers		Phosphoric Acid Sodium Phosphate 8-Oxyquinoline

The 20% dilution factor was tested by experiment. Walter research indicated that at concentrations greater than 85%, the peroxide would detonate rather than decompose in a controlled fashion.

The additives to the T-Stoff were to stabilise it, preventing it from decomposing during storage.

Walter Werke had also done a lot of research into suitable materials for engine components, as a number of metals will spontaneously decompose T-Stoff. To be avoided, were copper and lead and any organic materials. At least one explosion at the Japanese factory attempting to develop their own copy of the Walter engine, was due to using an organic-based gasket within a pump.

All organic and combustible materials had to be avoided, because contact with the 85% peroxide would cause spontaneous combustion. Peroxide is also extremely caustic and contact with the skin would result in serious burns in seconds. Therefore, during any operations involving the movement or dispensing of T-Stoff, hoses of running water were always on hand to wash away and dilute any accidental spillage.

Materials that could be used, were austenitic steels, aluminium and polyvinylchloride (PVC) products.

C-Stoff - In Detail 2

Methyl Alcohol	CH3OH	57% by Weight
Hydrazine Hydrate	N2H4.H2O	30% by Weight
Water	H2O	13% by Weight
Catalyst 431 Potassium Cuprous Cyanide	K3Cu(CN)4

The fuel mixture was again discovered through careful experiment. The methyl alcohol (which was referred to as M-Stoff), was mixed with hydrazine hydrate (B-Stoff) which promoted an auto-ignition reaction in the combustion chamber and smooth combustion during operation.

An ideal ratio would have been to use 50% B-Stoff, but the experiments showed that a 30% ratio mixture was just as effective and a cheaper option.

The useable fuel was produced by diluting the chemical components with water.

To decompose the T-Stoff on demand, required the presence of a chemical catalyst to promote the reaction. A number of chemical salts carry this property, including manganese salts. However, in the final Walter motors, potassium cuprous cyanide was used, called Catalyst 431. This copper salt was preferred, as it did not produce any deposits in the motor during combustion.

The catalyst itself was mixed in bulk with the C-Stoff fuel in the storage tanks. The liquid was then blown through with air to mix the catalyst and distribute it evenly in the propellant.

During operation, the correct proportions of C-Stoff and T-Stoff were sprayed into the combustion chamber. The presence of the catalyst decomposed the peroxide and the resultant heat of reaction with the presence of the hydrazine hydrate caused the auto-ignition of the methyl alcohol fuel.

The correct ratio of chemical fuels was C-Stoff:T-Stoff, 0.36:1. However, in order to more closely guarantee combustion, a slight excess of T-Stoff at the combustion chamber was preferred, so the actual ratios were closer to 0.29-0.32:1.

The Reactions 2

The peroxide, sprayed into intimate contact with the fuel in the combustion chamber undergoes the following chemical reactions.

With the Hydrazine Hydrate, the Peroxide is decomposed into nitrogen and very high temperature steam.

The methanol reacts with the peroxide to produce carbon dioxide and again water, although as we know, the temperature of reaction raises the state of this product to super-heated steam.

As a result, with complete combustion, the exhaust gases are comparatively safe and inert, although the temperature of the jet efflux will be in excess of 1800^o centigrade.

In the earlier Walter motors for the Messerschmitt Me 163A Series, the "cold" reaction was initiated by a permanganate catalyst which stained the motor efflux purple.

Here, the catalyst was more neutral, and the motor exhaust was much paler, with a yellow/green, almost transparent colour, until the steam condensed into a dense vapour trail in the air. The power of the reaction, the velocity of exhaust gases and the narrowness of the venturi opening of the motor often led to "diamond" shock waves appearing in the high speed exhaust as Messerschmitt Komet aircraft began their "sharp starts" at take-off. The noise is described in a number of accounts in very colourful language, but must have been ear-splitting.

References.

1	Baxter, AD: Walter Rocket Motors for Aircraft. RAE Technote Aero 1668 September 1945
2	Baxter, AD: Walter Experience with Hydrogen Peroxide and Related Chemical and Metallurgical Features. RAE Technote Aero 1669 July 1945

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