Kevin Johnson previously wrote:David just pointed out that iso-octane has numerous isomers, all with varying octane ratings. The engineers at the time simply did not foresee an issue with arbitrarily declaring iso-octane as having 100 octane rating and n-heptane as having 0 octane rating. So the definitions (hence methods) are NOT self-consistent.
140Air wrote:I think they did understand the arbitrariness of using an octane/heptane rating system and they knew the isomers of iso-octane.
About this time period there was a lot of work going on in atomic orbital theory. Someone probably understood about isomers of iso-octane but I do not think it was considered in automotive engineering or research. Prior to iso-octane, toluene was used and no mention was made of the three isomers. See Ricardo, for example:* [
my emphasis]
Page 10
... out on behalf of the Asiatic Petroleum Co., a sample of petrol, consisting mainly of paraffins
from which nearly all the aromatics had been removed by sulphonation, was taken as zero, and at
the other end of the scale pure toluene was chosen; the relative tendency of different fuels to
detonate was then expressed in terms of their “toluene value,” i.e. the equivalent proportion of
toluene which it would be necessary to mix with the standard aromatic free petrol in order to give
it the same tendency to detonate as that of the sample under examination. Later investigation showed
that the standard “aromatic free” petrol which contained about 35 per cent of naphthenes and the
lighter members of the paraffin series, was by no means the worst offender as regards detonation,
and that in fact several samples of commercial petrol were actually considerably worse. Also it was
found that toluene was not so effective in resisting detonation as ethyl alcohol.
Since, however, the expression “toluene value” has become rather widely used, it is probably better to
retain the term. Table I gives the toluene values and the highest useful compression for various fuels.
The highest useful compression ratio may be defined as the highest ratio at which a particularly efficient
engine used for the purpose of investigating the behaviour of fuels could be operated without detonation
at any mixture strength or with any ignition timing, with a standard amount of preheating to the carburettor,
and at a speed of 1500 R.P.M. It is therefore purely a relative term; that is to say, its absolute value
applies only to one particular type of engine operated under one given set of conditions, but its relative
value is applicable to any type of engine and under any conditions, as will be shown later. In this connection
reference may be made to the common belief that the rate of burning of the fuel, though one of the factors
controlling detonation, forms a limit to the speed at which an engine can run.
*
http://www.scribd.com/doc/40610101/The- ... rdo#scribd
1931
PREFACE TO NEW EDITION
The present volume is a revised and somewhat extended edition of Vol. II of The Internal-Combustion Engine
published in 1923. During the seven years which have elapsed since the above volume was published progress has
been considerable; it has, however, for the most part taken the form of improving and consolidating existing
orthodox design, and the only important new development which has arisen during this period is the achievement
of the high-speed Diesel. Since progress has, to a large extent, followed along the lines foreshadowed in the
original volume, and since also this volume dealt mainly with general principles rather than specific designs,
there has been little need for actual revision. The present volume therefore contains additions rather than
alterations, and a new chapter has been added dealing with the high-speed Diesel engine.
140Air wrote: Their results were self-consistent in that each system independently gave consistent results when the specified lab conditions and procedures were followed. No respectable researcher would ever publish a system that was not at least self-consistent. And, no non self-consistent system would ever be adopted. That was all they could do to create a rating system. Today we couldn't do much better in creating a one dimensional scale of fuel behavior.
Clearly Ricardo and others
hoped that the system was self-consistent, but lacking even the recognition of toluene isomers for an "absolute value" condition set, it was not.
