Taking a stab at how the engine compartment layout change affects the overall engine compartment heat just for fun. The following numbers are ballparks for a PT425.
Typically, a gallon of gas contains about 115,000 Btu per gallon. At a rate of consumption of 2.2 gallons per hour (full load), this equates to 253,000 Btu per hour of chemical energy. Say combustion is 95% efficient; this results in 240,000 Btu per hour of heat energy. Mechanical energy created by the engine to drive the oil pumps equates to approx. 64,000 Btu per hour of heat energy. This leaves 176,000 Btu per hour of heat energy that must be removed from the engine. Heat from the engine is removed via the engine cooling fan, and the exhaust. (If I have estimated correctly, it's been awhile since I ran these types of numbers; the exhaust component is worth about 104,000 Btu per hour, and the engine cooling fan exhaust accounts for 72,000 Btu per hour.) Now some of the engine mechanical energy is lost due to hydraulic efficiency and I estimate a full load heat rejection of some 13,000 Btu per hour to the hydraulic cooler (minus any cooling taking place in the reservoir and hydraulic circuit). A total of 189,000 Btu per hour heat rejection working at maximum capacity, thats a lot of heat to deal with. (Many single family homes have heating units just slightly smaller than this). Us PT owners know that the engine compartment can get very hot.
In the previous engine compartment layout, the engine cooling fan pulls air in from the front of the engine bay, close proximity to the hydraulic reservoir. This will tend to preheat the air supply to the engine cooling fan to some degree. The engine cooling air and at least half the exhaust heat (the other exhaust half is blown out) merge at the back of the engine compartment. When the hydraulic cooling fan clicks on, it pulls a good amount of this heat up through the hydraulic radiator. (It also helps cool the engine compartment by pulling this heat out, but loads up the hydraulic radiator). The hotter the hydraulic oil, the more the engine cooling air is preheated (higher engine temps and so on). The battery and other components sitting in the back are exposed to this hot environment.
With the new layout, the Engine cooling fan brings in ambient outside air, no preheating, no pulling air around a PTO and variable volume pump. With PTs new muffler design and insulation, a significant source of the engine compartment heat load is removed. The heat stays in the exhaust and gets mostly blown outside the engine compartment. Now some of the heated engine cooling air is pulled up into the hydraulic radiator, but significantly less. The benefits from a heat load stand point:
·Engine should run cooler
·Hydraulic oil and reservoir should run cooler
·Battery is in a cooler environment, which should help useful life.
·Lower engine compartment temps which should help prevent aging of the rubber hydraulic hoses, and the like.
I think that the previous design is sufficient, but the new changes are an improvement from a heat load management situation, plus better access to components to boot. It would be nice to compare the old and new side by side and measure any of these theoretical differences. Now in the winter, the previous layout might work best since it helps keeps the temperatures up in the operating band. Just my 2 cents for the fun of it. What da think? /forums/images/graemlins/laugh.gif
Duane
Typically, a gallon of gas contains about 115,000 Btu per gallon. At a rate of consumption of 2.2 gallons per hour (full load), this equates to 253,000 Btu per hour of chemical energy. Say combustion is 95% efficient; this results in 240,000 Btu per hour of heat energy. Mechanical energy created by the engine to drive the oil pumps equates to approx. 64,000 Btu per hour of heat energy. This leaves 176,000 Btu per hour of heat energy that must be removed from the engine. Heat from the engine is removed via the engine cooling fan, and the exhaust. (If I have estimated correctly, it's been awhile since I ran these types of numbers; the exhaust component is worth about 104,000 Btu per hour, and the engine cooling fan exhaust accounts for 72,000 Btu per hour.) Now some of the engine mechanical energy is lost due to hydraulic efficiency and I estimate a full load heat rejection of some 13,000 Btu per hour to the hydraulic cooler (minus any cooling taking place in the reservoir and hydraulic circuit). A total of 189,000 Btu per hour heat rejection working at maximum capacity, thats a lot of heat to deal with. (Many single family homes have heating units just slightly smaller than this). Us PT owners know that the engine compartment can get very hot.
In the previous engine compartment layout, the engine cooling fan pulls air in from the front of the engine bay, close proximity to the hydraulic reservoir. This will tend to preheat the air supply to the engine cooling fan to some degree. The engine cooling air and at least half the exhaust heat (the other exhaust half is blown out) merge at the back of the engine compartment. When the hydraulic cooling fan clicks on, it pulls a good amount of this heat up through the hydraulic radiator. (It also helps cool the engine compartment by pulling this heat out, but loads up the hydraulic radiator). The hotter the hydraulic oil, the more the engine cooling air is preheated (higher engine temps and so on). The battery and other components sitting in the back are exposed to this hot environment.
With the new layout, the Engine cooling fan brings in ambient outside air, no preheating, no pulling air around a PTO and variable volume pump. With PTs new muffler design and insulation, a significant source of the engine compartment heat load is removed. The heat stays in the exhaust and gets mostly blown outside the engine compartment. Now some of the heated engine cooling air is pulled up into the hydraulic radiator, but significantly less. The benefits from a heat load stand point:
·Engine should run cooler
·Hydraulic oil and reservoir should run cooler
·Battery is in a cooler environment, which should help useful life.
·Lower engine compartment temps which should help prevent aging of the rubber hydraulic hoses, and the like.
I think that the previous design is sufficient, but the new changes are an improvement from a heat load management situation, plus better access to components to boot. It would be nice to compare the old and new side by side and measure any of these theoretical differences. Now in the winter, the previous layout might work best since it helps keeps the temperatures up in the operating band. Just my 2 cents for the fun of it. What da think? /forums/images/graemlins/laugh.gif
Duane
