Excessive acidity in alcohol based fuels accelerates engine corrosion. Total Acid Number (TAN) accounts for all titratable acids regardless of their strength and is therefore not suitable to accurately predict the corrosion potential. pHe, on the other hand measures the strength of the acids present in the sample. Therefore, pHe is the better parameter for manufacturers to monitor the corrosion potential, maintain the quality of their product, and maximize profits.
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Measurement of pHe in ethanol and ethanol fuel blends is standardized by ASTM D6423 and EN 15490. Application Notes describing the measurement of pHe are available free of charge from Metrohm.
The design of the sensor is crucial for accurate pHe measurements. The ASTM standard recommends a high leak-rate sleeve junction reference electrode and a large membrane glass measuring electrode, as these perform best for measurements of alcohol fuels. The Metrohm EtOH Trode is one of two sensor explicitly mentioned by ASTM D6432 as suitable for pHe measurements in ethanol and ethanol fuel blends.