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Sound pressure level (SPL) measurements of vehicle coast-by runs of a passenger vehicle were performed across a range of temperatures. A controlled test track was used for the runs with six different sets of tires. A small but significant reduction of noise level with positive temperature increases was observed for some but not all tires. The reduction was evident in two of the tires at 53 kph and five of the tires at 80 kph. The SPL of the other tires showed little or no sensitivity to temperature. Frequency analysis of the tire noise showed that noise content above 1000 Hz is most affected by temperature change and noise in the range of 1200 to 2000 Hz is particularly sensitive to temperature changes. However, differences in SPL due to speed and tire type were much greater than that due to temperature

This is the second part of a study on using port water injection to quantifiably enhance the knock performance of fuels. In the United States, the metric used to quantify the anti-knock performance of fuels is Anti Knock Index (AKI), which is the average of Research Octane Number (RON) and Motor Octane Number (MON). Fuels with higher AKI are expected to have better knock mitigating properties, enabling the engine to run closer to Maximum Brake Torque (MBT) spark timing in the knock limited region. The work done in part I of the study related increased knock tolerance due to water injection to increased fuel AKI, thus establishing an ‘effective AKI’ due to water injection. This paper builds upon the work done in part I of the study by repeating a part of the test matrix with Primary Reference Fuels (PRFs), with iso-octane (PRF100) as the reference fuel and lower PRFs used to match its performance with the help of port water injection.