10. Basic Engine and Instrument Settings and Standard Operating Conditions
10.1 Installation of Engine Equipment and
Instrumentation - Installation of the engine and instrumentation requires placement of the engine on a suitable foundation and hook-up of all utilities. Engineering and technical support for this function is required, and the user shall be responsible to comply with all local and national codes and installation requirements.
10.1.1 Proper operation of the CFR engine requires assembly of a number of engine components and adjustment of a series of engine variables to prescribed specifications. Some of these settings are established by component specifications, others are established at the time of engine assembly or after overhaul, and still others are engine running conditions that must be observed or determined by the operator during the testing process.
10.2 Conditions Based on Component Specifications:
10.2.1 Engine Speed - 600 more or less 6 rpm, when the engine is firing, with a maximum variation of 6 rpm occurring during a rating. Engine speed, while firing, shall not be more than 3 rpm greater than when it is motoring without combustion.
10.2.2 Indexing Flywheel to Top-Dead-Center (tdc) - With the piston at the highest point of travel in the cylinder, set the flywheel pointer mark in alignment with the 0° mark on the flywheel in accordance with the instructions of the manufacturer.
10.2.3 Valve Timing - The engine uses a four-stroke cycle with two crankshaft revolutions for each complete combustion cycle. The two critical valve events are those that occur near tdc; intake valve opening and exhaust valve closing. See Annex A4 for camshaft timing and valve lift measurement procedures.
10.2.3.1 Intake valve opening shall occur 10.0 more or less 2.5° after-top-dead-center (atdc) with closing at 34° after-bottom-dead-center (abdc) on one revolution of the crankshaft and flywheel.
10.2.3.2 Exhaust valve opening shall occur 40° before-bottom-dead-center (bbdc) on the second revolution of the crankshaft and flywheel, with closing at 15.0 more or less 2.5° atdc on the next revolution of the crankshaft and flywheel.
10.2.4 Valve Lift - Intake and exhaust cam lobe contours, while different in shape, shall have a contour rise of 0.246 to 0.250 in. (6.248 to 6.350 mm) from the base circle to the top of the lobe. The resulting valve lift shall be 0.238 more or less 0.002 in. (6.045 more or less 0.05 mm). See Annex A4 for camshaft timing and valve lift measurement procedure.
10.2.5 Intake Valve Shroud - The intake valve has a 180° shroud or protrusion just inside the valve face to direct the incoming fuel-air charge and increase the turbulence within the combustion chamber. This valve stem is drilled for a pin, which is restrained in a valve guide slot, to prevent the valve from rotating and thus maintain the direction of swirl. The valve shall be assembled in the cylinder, with the pin aligned in the valve guide, so that the shroud is toward the spark plug side of the combustion chamber and the swirl is directed in a counterclockwise direction if it could be observed from the top of the cylinder.
10.2.6 Carburetor Venturi - A 9/16-in. (14.3-mm) venturi throat size shall be used regardless of ambient barometric pressure.
10.3 Assembly Settings and Operating Conditions:
10.3.1 Direction of Engine Rotation - Clockwise rotation of the crankshaft when observed from the front of the engine.
10.3.2 Valve Clearances:
10.3.2.1 Engine Stopped and Cold - Clearance between the valve stem and valve rocker half-ball, set upon assembly before the engine is operated can provide the controlling engine running and hot clearance. With the engine at tdc on the compression stroke, the appropriate cold clearances are as follows:
These clearances should ensure that both valves have sufficient clearance to cause valve seating during engine warmup. The adjustable-length valve push-rods shall be set so that the valve rocker adjusting screws have adequate travel to permit the final clearance setting.
10.3.2.2 Engine Running and Hot - The clearance for both intake and exhaust valves shall be set to 0.008 more or less 0.001 in. (0.20 more or less 0.025 mm), measured under standard operating conditions with the engine running at equilibrium conditions on a 90-O.N. PRF blend.
10.3.3 Oil Pressure - 172 to 207 kPa (25 to 30 psi). See Annex A4 for the procedure to adjust crankcase lubricating oil pressure.
10.3.4 Oil Temperature - 57 more or less 8°C (135 more or less 15°F).
10.3.5 Cylinder Jacket Coolant Temperature - 100 more or less 1.5°C (212 more or less 3°F) constant within more or less 0.5°C (more or less 1°F) during a rating.
10.3.6 Intake Air Temperature - 52 more or less 1°C (125 more or less 2°F) is specified for operation at standard barometric pressure of 101.0 kPa (29.92 in. Hg). IATs for other prevailing barometric pressure conditions are listed in Annex A6 (see Tables A6.4 and A6.5). If IAT tuning is used to qualify the engine as fit-for-use, the temperature selected shall be within more or less 22°C (more or less 40°F) of the temperature listed in Annex A6 (Tables A6.4 and A6.5) for the prevailing barometric pressure and this temperature shall then be maintained within more or less 1°C (more or less 2°F) during a rating.
10.3.6.1 The IAT required to qualify the engine in each TSF blend O.N. range shall also be used for rating all sample fuels in that O.N. range during an operating period.
10.3.7 Intake Air Humidity - 0.00356 to 0.00712 kg water per kg (25 to 50 grains of water per lb) of dry air.
10.3.8 Cylinder Jacket Coolant Level:
10.3.8.1 Engine Stopped and Cold - Treated water/coolant added to the cooling condenser-cylinder jacket to a level just observable in the bottom of the condenser sight glass will typically provide the controlling engine running and hot operating level.
10.3.8.2 Engine Running and Hot - Coolant level in the condenser sight glass shall be within more or less 1 cm (more or less 0.4 in.) of the LEVEL HOT mark on the coolant condenser.
10.3.9 Engine Crankcase Lubricating Oil Level:
10.3.9.1 Engine Stopped and Cold - Oil added to the crankcase so that the level is near the top of the sight glass will typically provide the controlling engine running and hot operating level.
10.3.9.2 Engine Running and Hot - Oil level shall be approximately mid-position in the crankcase oil sight glass.
10.3.10 Crankcase Internal Pressure - As measured by a gage or manometer connected to an opening to the inside of the crankcase through a snubber orifice to minimize pulsations, the pressure shall be less than zero (a vacuum) and is typically from 25 to 150 mm (1 to 6 in.) of water less than atmospheric pressure. Vacuum shall not exceed 255 mm (10 in.) of water.
10.3.11 Exhaust Back Pressure - As measured by a gage or manometer connected to an opening in the exhaust surge tank or main exhaust stack through a snubber orifice to minimize pulsations, the static pressure should be as low as possible, but shall not create a vacuum nor exceed 255 mm (10 in.) of water differential in excess of atmospheric pressure.
10.3.12 Exhaust and Crankcase Breather System Resonance - The exhaust and crankcase breather piping systems shall have internal volumes and be of such length that gas resonance does not result. See Appendix X2 for a suitable procedure to determine if resonance exists.
10.3.13 Belt Tension - The belts connecting the flywheel to the absorption motor shall be tightened, after an initial break-in, so that with the engine stopped, a 2.25-kg (5-lb) weight suspended from one belt halfway between the flywheel and motor pulley shall depress the belt approximately 12.5 mm (0.5 in.).
10.3.14 Basic Rocker Arm Carrier Adjustment:
10.3.14.1 Basic Rocker Arm Carrier Support Setting - Each rocker arm carrier support shall be threaded into the cylinder so that the distance between the machined surface of the cylinder and the underside of the fork is 31 mm (1 7/32 in.).
10.3.14.2 Basic Rocker Arm Carrier Setting - With the cylinder positioned so that the distance between the underside of the cylinder and the top of the clamping sleeve is approximately 16 mm (5/8 in.), the rocker arm carrier shall be set horizontal before tightening the bolts that fasten the long carrier support to the clamping sleeve.
10.3.14.3 Basic Rocker Arm Setting - With the engine on tdc on the compression stroke, and the rocker arm carrier set at the basic setting, set the valve adjusting screw to approximately the mid-position in each rocker arm. Then adjust the length of the push rods so that the rocker arms shall be in the horizontal position.
10.3.15 Basic Spark Setting - 13° btdc regardless of cylinder height.
10.3.15.1 The digital timing indicator currently supplied with CFR engine units, or the graduated spark quadrant formerly supplied, shall be in proper working order and calibrated so that the time of ignition is correctly displayed with reference to the engine crankshaft.
10.3.15.2 Basic Ignition Timer Control Arm Setting - If the CFR engine is equipped with an ignition control arm assembly, the knurled clamping screw on the control arm shall be loose so that the linkage is ineffective.
10.3.15.3 Ignition Timer Basic Transducer to Rotor Vane Gap Setting - 0.08 to 0.13 mm (0.003 to 0.005 in.).
10.3.16 Spark Plug Gap - 0.51 more or less 0.13 mm (0.020 more or less 0.005 in.).
10.3.17 Basic Cylinder Height Setting - Thoroughly warm up the engine under essentially standard operating conditions. Shut the unit down and check that the ignition is turned off and fuel cannot enter the combustion chamber. Install a calibrated compression pressure gage assembly on the engine, motor the engine, and adjust the cylinder height so that the unit produces the basic compression pressure for the prevailing barometric pressure as prescribed by the relationship of Fig. 2.
10.3.17.1 Index the cylinder height measurement device(s) to the appropriate value, uncompensated for barometric pressure, as follows:
10.3.17.2 Refer to Annex A4 for a detailed cylinder height indexing procedure.
10.3.18 Fuel-Air Ratio - The fuel-air ratio (mixture proportion) for each sample fuel and PRF involved in the determination of an O.N. result shall be that which maximizes the K.I.
10.3.18.1 Fuel-air ratio is a function of the effective fuel level in the vertical jet of the standard carburetor assembly and is typically indicated as the fuel level in the appropriate carburetor sight glass.
10.3.18.2 The fuel level that produces maximum K.I. shall be from 0.7 to 1.7 in., referenced to the centerline of the venturi. If necessary, change the carburetor horizontal jet size (or equivalent restrictive orifice device) to satisfy the fuel level requirement.
10.3.19 Carburetor Cooling - Circulate coolant through the coolant passages of the carburetor whenever there is evidence of premature vaporization in the fuel delivery passages. Release of hydrocarbon vapors from the sample fuel can result in uneven engine operation or erratic K.I. reading and is usually indicated by bubble formation or abnormal fluctuation of the fuel level in the sight glass.
10.3.19.1 Coolant - Water or a water/antifreeze mixture.
10.3.19.2 Coolant Temperature - The liquid coolant delivered to the carburetor coolant exchangers shall be cold enough to prevent excessive vaporization but not colder than 0.6°C (33°F) or warmer than 10°C (50°F).
10.3.20 Instrumentation:
10.3.20.1 Knockmeter Reading Limits - The operational range for K.I. readings on the knockmeter shall be from 20 to 80. Knock intensity is a nonlinear characteristic below 20 and the knockmeter has the potential to be nonlinear above 80.
10.3.20.2 Detonation Meter Spread and Time Constant Settings - Optimize these variables to maximize spread commensurate with reasonable K.I. signal stability. Refer to Procedure sections and Annex A4 for further detail.
10.3.20.3 Knockmeter Needle Mechanical Zero Adjustment - With the detonation meter power switch in the OFF position, and the meter switch in the ZERO position, set the knockmeter needle to ZERO using the adjusting screw provided on the knockmeter face.
10.3.20.4 Detonation Meter Zero Adjustment - With the detonation meter power switch in the ON position, the meter switch in the ZERO position, the time constant switch on 3, and the meter reading and spread controls in their nominal operating positions, set the needle of the knockmeter to read ZERO using the detonation meter zero adjusting screw, which is to the left of the meter switch on the detonation meter and covered by a knurled cap.