Effect of Combustion Time on Knock in a Spark-Ignition Engine 530242
IF combustion of fuel-air mixtures is completed in an engine before chemical reactions have had time to take place, no knock-producing materials are formed - thus solving a chronic, critical problem. Knock can be controlled by using fuels in which reactions proceed at a slow rate. It can be reduced by speeding up the burning of the charge.
The author of this paper has explored the relationship between combustion time and knocking tendency, and has reported the results of a number of new tests.
He used a single-cylinder engine equipped with 17 spark plugs which were especially designed and fabricated for these tests. He shows how far octane requirements can be reduced under certain conditions.
The decrease was found to be significant when combustion time was reduced by firing 17 spark plugs simultaneously instead of firing one plug in the normal location. The decrease was less when the combustion chamber contained deposits than when no deposits were present. When using single ignition the location of the end gas was considered as important as combustion time in determining octane requirement.