Search Results

During 1970-1971, 15 organizations participated in a Coordinating Research Council program to compare the influence of unleaded and leaded gasolines on octane requirement increase (ORI). A total of 147 1971 model cars (47 pairs and 53 individual cars) were operated for 8000-20,000 miles using driving schedules prescribed by each participant One car of each pair was run on an unleaded fuel of 91-95 Research octane number (RON) and the other on a leaded fuel of similar quality. For paired cars, the average ORI was 5.8 RON for unleaded and 3.8 RON for leaded fuel cars. The ORI difference of 2.0 RON for paired cars was slightly less than the average ORI difference of 2.5 RON for all 75 unleaded and 48 leaded cars. In a supplemental program, results in 20 cars showed an average ORI difference of only 0.3 RON between unleaded and low-lead fuel cars.

The Coordinating Research Council (CRC) conducted a program during the summer of 1972 to determine the decrease in octane number requirement with altitude for current model cars. The study was made because the engines in these cars run hotter and leaner than earlier models, no information was available on altitude corrections for unleaded fuels, and no adjustment was planned for the so-called 91 octane gasolines in the symbol system being developed by ASTM/SAE. Maximum octane number requirements were determined on thirty-nine 1971-1972 model cars, six 1967-1970 model cars, and four light-duty military trucks at sea level, 2000, and 4000 ft on three series of full-boiling range fuels and primary reference fuels. Results indicate that the decrease in octane number requirement per inch of mercury decrease (approximately per 1000 ft) is about two units for 1971-1972 cars and 1.5 units for the 1967-1970 cars and the four military trucks.

In 1962 and 1964 the Coordinating Research Council (CRC) evaluated the vapor locking characteristics of about 40 selected new model cars during centralized programs at Yuma, Arizona. Volatility tolerances were determined during acceleration following a hot soak at approximately 100 F ambient using two reference fuel series with diverse front-end volatilities. Fifty per cent of the 1962 model cars tested had a limiting vapor pressure equal to or less than 8.4 lb with the high volatility fuels and 9.7 lb with the low volatility fuels. Comparable values in the 1964 program were 8.9 lb for the high and 10.4 lb for the low volatility fuels. Analytical results obtained on vehicle tank samples for the first time during 1964 showed that limiting temperature at a given vapor-to-liquid ratio also was a useful parameter in defining car volatility tolerances.

A test technique has been developed that permits evaluation of passenger car hot start and run characteristics at various severity levels with a minimum of instrumentation. The most critical of several test conditions investigated in five cars at approximately 95 F ambient were a 20-mile warmup at 70 mph followed by a 20-minute engine-off soak period.A hot start and run is defined as an engine start followed by an idle period of at least one minute. The technique gives satisfactory results when using adjusted RVP for two stalls or for a 4 sec start. Two fuel series are desirable but one series, more severe than average commercial summer gasolines, should be satisfactory for survey purposes.

During March 1969, the Coordinating Research Council (CRC) conducted a test program at Pasco, Wash., to investigate a driveability test procedure and the effects of fuel volatility on driveability during cool weather (30-50 F). Fifteen late-model automobiles and eight fuels with different volatility characteristics were evaluated. Driveability was rated subjectively during cold-start and driveaway, and after the car had warmed-up. For the cold phase, driveability was related to fuel volatility as defined by the front-end and mid-boiling range of the fuel distillation curves. However, driveability during the warm phase was not affected by fuel volatility within the range of fuels tested.

During the fall and winter of 1970-1971, the Coordinating Research Council (CRC) contracted with Southwest Research Institute for the latter to conduct a pilot program on 10 pairs of 1971 model cars to compare the influence of leaded and unleaded fuels on octane requirement increase (ORI). The cars were operated for 8,000-10,000 miles in the San Antonio area using a prescribed city-suburban driving schedule. One car of each pair was run on a commercially available leaded gasoline of 93 Research octane number (ON) and the other on a specially prepared unleaded fuel of similar quality. Differences in ORI for the two fuels ranged from 0-3.5 ON within car pairs. The average ORI of 4.0 ON for leaded fuel cars and 4.6 ON for unleaded fuel cars was not significantly different above the 80% confidence level.