BS ISO 8893:2021 pdf download – Forestry machinery — Portable brushcutters and grass-trimmers — Engine performance and fuel consumption
4 Accuracy of measurements
4.1 Torque: ±2 % of measured torque. The torque measuring system shall be calibrated to take friction
losses into account.
4.2 Engine speed: ±2 % of measured speed.
4.3 Fuel consumption: ±2 % of measured consumption.
4.4 Fuel temperature: ±2 °C.
4.5 Engine inlet air temperature: ±2 °C.
4.6 Barometric pressure: ±100 Pa.
5 Power correction factors
The power correction factor is the coefficient to determine the engine power under the reference atmospheric conditions specified in 5.2. It can be calculated using Formula (1):
the operator is foreseen in the instructions, an according adjustment to achieve the maximum possible power is allowed.
6.4 Power-consuming auxiliaries shall be turned off.
6.5 No extra engine cooling or air supply is allowed.
6.6 The fixture used to mount the engine to the dynamometer should be verified that it does not influence the performance on the unit compared to an “in-use” condition.
6.7 The engine shall be coupled to the brake power test bench in such a manner that the engine crankshaft is aligned with the brake shaft and connected to it with a flexible coupling. The use of the engine clutch is optional.
6.8 The engine shall be run in, in accordance with the manufacturer’s instructions. If the engine was previously run in, this operation shall be omitted.
6.9 The fuel shall consist of petrol with a minimum octane (R+M)/2 of 87, measured according to ISO 5164, and, if it is a two-stroke engine, mixed with two-stroke oil according to the manufacturer’s recommendation. The density of the fuel shall be 680 kg/m 3 to 790 kg/m 3 at 15 °C.
7 Operating method
With the throttle in a fully open position, record the brake power, torque and fuel consumption as a function of the rotational frequency in steps of 300 r/min, starting from 900 r/min above peak power speed and decreasing down to 900 r/min below the peak torque speed.
Take the readings during the 10 s interval after the temperature has stabilized at each step, Table 1 is an example of how to record the data at each step. The engine temperature is stable when the engine coolant, block or head absolute temperature has settled within ±3 °C for at least 30 s. Take the readings at least over a rotational frequency range limited by the engine speed for maximum torque minus 900 r/min, and the engine speed for maximum power plus 900 r/min. If the engine speed is limited below the speed of maximum power plus 900 r/min, measure at the maximum speed achievable. If the engine does not run with a stable speed, carry out the test at the maximum possible stable speed. This speed shall, however, not be more than 480 r/min below the maximum achievable speed.
7.2.1 Determination of the peak power and peak torque engine speed
22.214.171.124 Prior to mounting the engine on the power test bench, warm up the engine by operating it. It is recommended operating the engine at any speed and at approximately 75 % of its expected maximum power. Continue the warm-up until the engine-stabilized temperature has been achieved. If applicable, set the idle speed adjuster and low speed mixture adjuster for best idling at the rotational frequency recommended by the manufacturer.
126.96.36.199 Run the engine at fully open throttle on the dynamometer bench and determine the engine speed at which the engine makes peak torque and the speed at which it makes peak power. If an adjustment of the fuel/air mixture by the operator is foreseen in the operator’s instructions, adjustment to achieve the peak power is allowed.
188.8.131.52 Record these speeds, as they will be used in determining the power curve in 7.2.2.
7.2.2 Determination of the power curve and fuel consumption curve
184.108.40.206 Prior to the test, record the ambient air temperature (°C) and air pressure (kPa) in Table 1.
220.127.116.11 Run the engine with fully open throttle at the engine speed of peak power plus 900 r/min until engine-stabilized temperature has been achieved.BS ISO 8893 pdf download.