ASTM D6812 tandard Practice for Ground-Based Octane Rating Procedures for Turbocharged/Supercharged Spark Ignition Aircraft Engines
6. Apparatus
6.1 Instrumentation:
6.1.1 The engine shall be equipped with the following instrumentation, which shall be accurate to within +/- 2 % of full scale unless noted otherwise.
6.1.1.1 Absolute Manifold Pressure Transducer - The location of the MAP sensor shall conform to engine manufacturer's specified location. Manifold pressures shall be measured with an accuracy of less than 2.5 mmHg and recorded to ensure proper engine behavior and repeatability.

6.1.1.2 Cooling Air Pressure Transducer, located so as to determine the pressure within the cowling.

6.1.1.3 Cooling Air Temperature Sensor, located either within the cowling or at the entrance to the cowling. If a thermocouple is utilized, it should extend at least a third of the way across the measured area.

6.1.1.4 Crankshaft Angle Encoder, if required for knock detection. The encoder shall have a sample resolution of at least 0.4° of crankshaft rotation. The encoder TDC pulse shall be aligned with the TDC of cylinder number one prior to octane rating.

6.1.1.5 Cylinder Head Temperature Sensors, installed in each cylinder. The sensing locations and types of thermocouples shall conform to the engine manufacturer's recommendations. The CHT measurements shall be accurate to within 1 % of full scale.

6.1.1.6 Exhaust Gas Temperature Sensors, on all cylinders. Installation shall conform to the manufacturer's recommended location and proper material selection. EGT probes are usually installed within 5 cm (2 in.) of the exhaust stack flange. The EGT probes shall be accurate to within 1 % of full scale.

6.1.1.7 Turbine Inlet Temperature Sensors, for each turbine. Installation shall conform to the manufacturer's recommended location and proper material selection. The TIT probes shall be accurate to within 1 % of full scale.

6.1.1.8 ManifoldAbsolute Temperature Sensor - Installation shall conform to the manufacturer's recommended location and proper material selection. The MAT probe shall be accurate to within 1 % of full scale.

6.1.1.9 Engine Speed Sensor - The dynamometer or propeller stand shall measure the engine shaft speed to determine power development. The engine speed sensor shall be accurate to within +/- 5 rpm.

6.1.1.10 Fuel Flow Meter - If the device is calibrated for a particular fuel, then the device shall be recalibrated for each different and subsequent fuel. Data should be reported in mass flow units. If applicable, vapor return flow rate shall also be measured to obtain the actual engine fuel consumption rate.

6.1.1.11 Fuel Pressure Transducers - Locations of fuel pressure transducers shall conform with that recommended by the engine manufacturer. One transducer is required for the metered fuel pressure, if necessary, and another is required for the pump outlet pressure. The fuel inlet pressure shall not fall below the minimum specified by the engine manufacturer during the rating process.

6.1.1.12 Induction Air Pressure Transducer, located so as to measure the pressure of the induction stream prior to the throttle plate.

6.1.1.13 Induction Air Temperature Sensor, located so as to measure the temperature of the induction stream prior to the throttle plate.

6.1.1.14 Knock Sensors - The referee method for knock detection is described in Annex A1. This method requires flush mounting piezoelectric transducers. All cylinders shall be monitored. These transducers are connected to charge amplifiers and shall be capable of measuring combustion pressures under a high temperature environment.

6.1.1.15 Oil Pressure Transducer - Location of pressure measurement shall conform to the engine manufacturer's specified location.

6.1.1.16 Oil Temperature Sensor - Location of temperature measurement shall conform to the manufacturer's specified location.

6.1.1.17 Torque Meter - The dynamometer or propeller stand shall measure the torque to determine power development. The torque measurement shall be accurate to within 1 % of full scale.

6.1.2 The engine should be equipped with the following instrumentation, which shall be accurate to within +/- 2 % of full scale unless noted otherwise.
6.1.2.1 Induction Air Flow Meter - Data should be presented in mass flow units.

6.1.2.2 Induction Air Humidity Sensor, located in either the induction air plenum or induction air duct. Data should be presented in absolute, rather than relative, quantities.

6.1.2.3 Outside Air Temperature Sensor, capable of measuring the ambient dry bulb temperature.

6.2 Data Acquisition:
6.2.1 The instrumentation listed in 6.1 shall be scanned and the data recorded at least once every 10 s by an automatic data acquisition system. The data shall be stored in a universal format (for example, comma separated values (CSV) for IBM compatible machines) that can be retrieved at a later date.

6.2.2 If in-cylinder pressures are recorded to determine knock intensity, the pressure data shall be sampled at a rate of at least 1800 samples per pressure cycle per cylinder for 100 consecutive engine cycles.

6.3 Power Absorption - The testing is to be performed in a ground-based test cell using either a dynamometer or propeller test stand that shall be capable of maintaining a constant speed to within +/- 5 rpm.
6.3.1 The power absorber shall be capable of providing loads for given engine speeds covering the entire range of the engine's operating envelope.

6.4 Fuel System:
6.4.1 The fuel supply shall have a disposable or cleanable filter. The filter shall allow the proper minimum fuel flow.

6.4.2 The fuel selection valve shall be capable of selecting at least two different fuel sources without the possibility of cross contamination of either source.

6.4.3 The fuel supply system shall comply with federal, state, and local regulations related with fire, hazards, and health issues.

7. Reagents and Materials
7.1 The MON of PRFs is confirmed by using Test Method D2700. All PRFs used for the engine octane ratings consist of blends of reference grade isooctane and n-heptane. The PRFs will be prepared in increments of one MON. All RFs used for engine octane rating consist of blends of reference grade isooctane and 3-MPA. The reference fuels will be prepared in increments of one weight % 3-MPA. (Warning - PRF and RF are flammable and the vapors are harmful. Vapors may cause flash fire.)
7.1.1 Isooctane (2,2,4-trimethylpentane) shall be no less than 99.75 % by volume pure, contain no more than 0.10 % by volume n-heptane, and contain no more than 0.5 mg/L (0.002 g/U.S. gal) of lead. (Warning - Isooctane is flammable and its vapor is harmful. Vapors may cause flash fire.)

7.1.2 n-Heptane shall be no less than 99.75 % by volume pure, contain no more than 0.10 % by volume isooctane, and contain no more than 0.5 mg/L (0.002 g/U.S. gal) of lead. (Warning - n-heptane is flammable and its vapor is harmful. Vapors may cause flash fire.)

7.1.3 MPA shall be no less than 99 % by volume pure, contain no more than 0.10 % by volume isooctane, and contain no more than 0.5 mg/L (0.002 g/U.S. gal) of lead. (Warning - 3-MPA is flammable and its vapor is harmful. 3-MPA is toxic by inhalation, in contact with skin, and if swallowed. Danger of cumulative effects. Vapors may cause flash fire.)

7.1.4 A sample shall be taken of each PRF and subjected to Test Method D2700 for motor octane verification.

7.1.5 A sample shall be taken of each RF and the amine content verified. Ensure reference fuel is a homogenous mixture under test conditions.

7.2 Fuels used for operations other than octane rating (for example, warm-up) shall not contain metallic additives and should be capable of satisfying the test engine's octane requirement under the conditions for the fuel to be used. (Warning - These fuels are flammable and their vapor is harmful. Vapors may cause flash fire.)

7.3 Engine oils used for break-in and normal operation shall be oils approved by the engine manufacturer for their respective operation. (Warning - Lubricating oil is combustible and its vapor is harmful.)