Hey tomo pauk,
re
Would it really be 130 grade fuel they used in, I assume, 1940?
The UK Air Ministry began using the single-cylinder CFR test method as standard in 1935orB4. The British Air Ministry subsequently developed a standard single cylinder RMR (Rich Mixture Rating) procedure based on a Pegasus engine 8:1 CR cylinder (which was representative of the 'most severe service engine' in use at the time) in which fuel batches were checked against the various reference fuels. The new CFR test method was designated the British Air Ministry modified Motor Method. The Pegasus type cylinder used by the test engine was later changed to a Hercules cylinder (I have no idea why). Note that the abbreviation B.A.M. stands for British Air Ministry.
The designation B.A.M.100 (or BAM.100) that we often see used to reference pre- and early-war UK '100 octane' was actually the
testing procedure designation that was to be used for proofing the fuel material batches, rather than the designation for the actual '100 octane'
fuel material. The UK started using the term BAM.100 in January 1937 as a provisional designation for the new '100 octane' fuel.
Approximately 1000 tons of '100 octane' Avgas was trialed at RAF Sqn level beginning in June 1937, with the tests ending in September 1938. These tests gave the Air Ministry important information as to what appeared practical to achieve with the new fuel and what possible fuel blends allowed the desired improvements in engine performance.
The lean and rich mixture 100/130 PNs were set in September 1938 and remained the same for the rest of the war. (I believe Snowygrouch referenced this as well in one of his posts but I could not find it using Snowygrouch, as the search term is no longer usable due to his leaving the forum.
) The BAM.100 testing procedure, which defined what method was to be used (in this case the British Air Ministry modified Motor Method for '100 octane') defined the PN (Performance Numbers) that had to be met by the actual fuel material. 72,000 tons of BAM.100 fuel were ordered in November 1938. First delivery of BAM.100 to England was in June 1939 (I think).
As to what fuel they actually used when testing the engines, all war-time engines were required by the Air Ministry DED/DERD to be tested using what they called a 'reference fuel' - ie a fuel that met the minimum standards set out in the test specification. There were different reference fuels for different grades - ie 73, 80, 87, 100, etc. The reference fuel used for testing BAM.100 had to result in PNs that matched or exceeded those of 100% iso-octane plus 4cc TEL per Impgal. So in theory at least, RR and the other UK engine manufacturers used the specified 100/130 PN reference fuels when they rated their engines.
After 1938 the fuel material
blends were allowed to change, but they all had to achieve the 100/130 PN using the BAM.100 testing procedure. Before 1940, due to the fact that they had not settled on the specific blends achievable and allowed, there was no formal DED number assigned to the '100 octane' fuel material. (The designator DED.2475 may have been assigned to the '100 octane' fuel material sometime during the war but I am not sure.) In early-1940 responsibility for the fuel material specification was transferred from DED to RDE, and British '100 octane' fuel material meeting the BAM.100 test requirements became RDE/F/100.
When I was researching the pre- and war-time fuels I found it interesting that when the UK was paying cash for the fuel purchases (prior to the US entry into the war and Lend-Lease) the US refineries and government agencies often referred to British orders for '100 octane' by variations of the BAM100 designation - due to the British purchasing agencies requiring the US refineries to use the same testing procedures as the UK refineries (or testing procedures that gave the same results, subject to approval by the UK). There were a fair number of memos passed back and forth between the US government agencies involved and the refineries complaining about the difficulties in meeting the requirement. Part of the problem was the rapid expansion in production and the learning curves, and part of it was due the attempts to use less aromatics and reduce the expense.
Incidentally, when the tankers arrived in England (and overseas) they were met by specialists who tested the fuel. The Air Ministry also ordered various amounts of aromatics and TEL and had them shipped with the fuel material if necessary - the intent being to add aromatics and/or TEL if so needed to bring the fuel material upto standard. One or more of the refineries in England was also tasked with producing the aromatics specifically for this purpose.