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What a Pyro does
A pyrometer is an exhaust temperature gauge that allows you to read an immediate change in exhaust temperature by receiving a temperature signal from a probe (thermocouple) that is inserted into the exhaust manifold. This constant monitoring of temperature changes alerts the driver to temperature problems well before indications would be received from a typical water temperature gauge. Equipment operators use pyrometers to diagnose engine problems and drive more efficiently, prolonging engine life and reducing fuel consumption.
The diesel engine is a phenomenal machine. It takes energy from heat and converts it into motion to transport goods. Excessive temperature is the greatest damaging factor to an engine. By monitoring the temperature of the exhaust, you can detect changes in temperature which may be the early signs of trouble. A pyrometer will indicate engine problems more efficiently than any other method.
Lets examine how a pyrometer will help you. The horsepower developed by the diesel engine depends on the amount of fuel being burned efficiently. Fuel and air must be delivered to the combustion chamber in the right quantity. It takes about 2,500 gallons of air for every gallon of fuel. Higher exhaust temperatures are the result of these basic causes:
1. Excessive fueling which is usually caused by a heavy foot or a faulty fuel system. Electronic engines can have problems which will show up first on the pyro. Note: The overfueling temperature increase is five degrees per pound of excess fuel burned.
2. A high intake ambient air temperature. Note: For every one degree increase in the external temperature there is a three degree increase in exhaust temperature.
3. Restricted air caused by: 1) Dirty air cleaners (intake air restriction). For every ten inches of vacuum there is a thirty degree increase in exhaust temperature. 2) High altitude. Note: There is a twenty five degree increase per 1,000 foot increase in altitude.
4. Headwinds/wind resistance
5. Lugging the engine, caused by improper throttle use or shifting.
Excessive heat is one enemy of the turbocharger. The maximum input temperature of a turbocharger is approximately 1,400°F. Temperatures above this will deteriorate the turbo housings, crack them and foul the compressor wheels. Intake and exhaust manifolds as well as cylinders will crack.
Excessive fueling will cause overspeeding or excessive revs resulting in high fuel consumption. Wasteful overspeeding and excessive heat damage the engine and turbo. Overspeeding will result in pistons striking and breaking valves. Prints of valves on the piston heads is an indication that the engine has been over revved. Injectors may stick as a result of overspeeding when a vehicle is going down grade and pushes the engine above governed speed. The governor shuts off all fuel to the injectors and deprives them of lubrication. Most diesels are protected against overspeeding by governors which should be correctly adjusted. Increasing the RPM's by changing the governor or allowing a vehicle to push the engine beyond its rated RPM will lead to engine damage. Incomplete fueling can also cause many problems. It is usually caused by restricted air supply. It results in a loss of horsepower and fuel is wasted. The unburned fuel will wash the lubricating oil off the cylinder walls. This can cause seized, burned or scored pistons and rings. Unburned fuel may also dilute and contaminate the lubricating oil. The injector cup spray holes may become carboned resulting in faulty injectors which help to create an even more unreliable fuel/air mixture.
Another situation to watch is when a hill is being crested. The engine must be cooled by shifting down and backing out of the throttle because the engine will cool down too fast. It is not good to let an engine cool down too much at the bottom of the hill before starting up again. When the engine is not being operated in the most efficient range, fuel is being wasted and engine damage will occur if the proper procedure is not followed.
The pyrometer is one of the first indicators of trouble in the engine. If an injector clogs, a cylinder or piston cracks, or an electronic injector has a problem, a pyrometer will note the change. The reason a pyrometer will call attention to engine problems faster is that a pyrometer measures the internal thermo-dynamics of an engine. The benefits are longer engine life, better fuel consumption, lower emissions and an indication of malfunctions before damage occurs.
Today's low RPM, fuel efficient engines operate at much lower temperatures than their predecessors. High temperature as well as temperature change are continued concerns. To make temperature changes easy to identify, ISSPRO, INC. has developed an instrument which features a 1200° face dial with a full 250° sweep. It is available in 2-1/16" and 3" diameters and a 3" dual scale for V or multi-engine installations.
To determine your safe maximum exhaust temperature, run a well-tuned engine at full RPM and horsepower on the inertia dynamometer or under a loaded pull. Note the exhaust temperature and subtract 200°. This is your safe maximum exhaust temperature. This temperature may be exceeded for a short period and will not cause serious damage. Stay in the upper one third of your temperature range as much as possible. Operation in the lower range isn’t as critical as exceeding the maximum range.
ISSPRO, INC.'s line of digital instruments are available in 2-1/16" diameter (commonly referred to as 2-inch Gauges). The range is 0 to 1990° and can be used on low temperature engines as well as high temperature applications. The instrument updates temperature three times per second for extreme accuracy. An automatic brightness control adjusts the display intensity for optimal visibility. An alarm feature is standard, flashing when a temperature of 1150°F is reached. An output is available that can be used to activate a light, buzzer or another alarm device.
The thermocouple is the power source of the whole system. Two different types of metal are induction welded together in the tip of the thermocouple. This assures a fast reaction time because the case tip and thermocouple are the same and the junction is protected from damage.
The tip is made of stainless steel and is filled with a ceramic material. This makes the probe solid and protects the internal wires from damage. The attached aircraft quality Kapton leads are then encased with a flexible wire braid to protect them from heat and abrasion. A spiral wound spring strain relief protects the wire as it exits the probe. When heat is applied to the junction a tiny voltage is produced and travels up the lead wire. It is important never to solder the lead wire as each solder joint will act as an additional junction generating voltage. This voltage will affect the accuracy of the instrument. The voltage is the read by the pyrometer. All of the pyrometers that we have put on our site use the ISSPRO type K thermocouple. This thermocouple produces -1.63mV at 0°F and 26.03mV at 1200°F, and is the most widely used.*
Hot engine shutdown is a major cause of turbocharger damage. To prevent this, engine manufacturers recommend idling an engine for a period of time before it is shut down. This allows oil to flow through the bearings and cool them. The goal is to reduce bearing temperature to 300°F. Using the ISSPRO Turbo Temp Monitor can achieve this. A thermocouple is mounted downstream of the turbocharger and monitors exhaust gas temperature and delays shutdown until 300°F is reached. Shutting the engine down cooled prevents dangerous deposits from forming and turbo life is increased. If you already have a pyrometer gauge installed, you can just tap into that system at the control box.