. Automotive industries . mixture is slightlygreater at the higher compression, and this no doubtaccounts for the fact that the pressure at which detona-tion commenced is higher at the higher compressionratios, instead of slightly lower as would otherwise beexpected due to the higher compression temperature. As a practical and ready means of determining thetoluene value of a fuel, it is interesting to note that thenew aniline test employed by chemists for determiningthe aromatic content of a fuel responds also to the naph-thene content, and therefore this test affords a fairlyaccurate measure
. Automotive industries . mixture is slightlygreater at the higher compression, and this no doubtaccounts for the fact that the pressure at which detona-tion commenced is higher at the higher compressionratios, instead of slightly lower as would otherwise beexpected due to the higher compression temperature. As a practical and ready means of determining thetoluene value of a fuel, it is interesting to note that thenew aniline test employed by chemists for determiningthe aromatic content of a fuel responds also to the naph-thene content, and therefore this test affords a fairlyaccurate measure of the tendency of the fuel to reason for this is shown by reference to Table III(which was printed in the preceding article on this sub-ject), giving, for various fuels, their observed toluenevalues and also their approximate compositions. It maybe seen from this table that the average toluene valueof the paraffins present in petrol is roughly — 10 percent. The average for the naphthenes is 4- 30 per 50 CO TO COMPRESSION RATIO Fig. 8The full lines show the indicated mean pressureobtained and the corresponding compression pres-sure (taken by modified Okill gauge) for varyingcompression ratios, and the throttle closed justsufficiently to prevent detonation of a fuel of lowtoluene value. The dotted line continuations showwhat would have been the resulting mean pressuresat the various ratios had the toluene value beensufficiently high to admit of full open throttle atthe highest compression ratio The average for the aromatic is 4- 75 per cent—thetoluene value of benzol being 67 per cent, of toluene 100per cent and of xylene 85 per cent. Although the results obtained from this series of in-vestigations into the factors controlling detonation per-mit of certain fairly definite conclusions being drawn,the writer feels that much still remains to be done, formany discrepancies still remain to be cleared up. Thefollowing conclusions and inferences may, ho
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