LP-GAS OCTAN NUMBERS AND THEIR RELATIONSHIP TO ENGINE PERFORMANCE 590269
An investigation has been made of the relationship between LP-Gas characteristics and the knock-limited performance of several bus and truck engines over a range of design and operating conditions. This work has shown that:
The knock-limited spark advance characteristics of LP-Gas blends in the engines tested could be rationalized in terms of the Research and Motor octane numbers calculated and determined for the blends.
The three most severe truck engines investigated in this program have an LP-Gas antiknock requirement of 90.5 octane number at a point called Severity “E”. A nomograph has been developed which can be used to define Severity “E” and can also be used to test an LP-Gas blend of known composition for its suitability in meeting this octane requirement.
Sufficient data were obtained in this program to demonstrate that if carburetor air or mixture temperatures are not controlled to reasonable limits, satisfactory knock-free operation will not be experienced in all heavy duty engines with pure propane.
The unique knock limited characteristics of LP-Gas in these heavy duty engines, basically designed for gasoline, suggest that a new approach is required to design mechanical octane numbers for gaseous fuels.