I m trying to work out the btu per hour on a 16 ltr 4 stroke turbo Diesel engine . The info I can share is that the turbo produces 31 psi boost the engine runs at 1650 rpm and the pyrometer averages 350 degrees celcius. Diesel burn is approximately 75 ltr per hour. Can anybody help
Btu measuring
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A gallon of diesel fuel is 120,000 btu, 75 ltrs is 20 gallons, so gross fuel input is
2.4 million BTU. Now if the engine was hooked to a constant load, generator, pump tec, and you knew the load, then the efficiency could be calculated, approximately.
A diesel is about 35% +/- efficient. so of the gross btu input about 840,000 of work is done.
I don't know if that is what you are looking for,
2.4 million BTU. Now if the engine was hooked to a constant load, generator, pump tec, and you knew the load, then the efficiency could be calculated, approximately.
A diesel is about 35% +/- efficient. so of the gross btu input about 840,000 of work is done.
I don't know if that is what you are looking for,
What exactly are you trying to measure the btu's of?
Machine Tom gave you good numbers as far as btu input vs. work done at the output shaft. The most efficient direct injection diesels will approach 40% efficiency, and the most modern turbo-diesel's with electronically controlled common-rail fuel injection can approach 50%.
Machine Tom gave you good numbers as far as btu input vs. work done at the output shaft. The most efficient direct injection diesels will approach 40% efficiency, and the most modern turbo-diesel's with electronically controlled common-rail fuel injection can approach 50%.
I am actually trying to work out the btu in the exhaust gas. It is an electronically controlled common rail engine and according to the computer the engine load averages 70% . I know this is not model engineering but I know there are a lot of knowledgable people on here. Thanks
Entropy455
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Ripcrow, I would be happy to do this calculation for you, but I require some additional information. (1) Is this an intercooled engine? (2) Is the 350 degree C exhaust temperature located upstream or downstream of the turbine wheel? (3) is this a 2 valve, or 4 valve head engine?
In the meantime, I will make some assumptions, and give you some numbers.
At sea level, on a 70 degree F day, air weighs about 0.07489 pounds per cubic foot. By compressing this air within a turbocharger’s compressor wheel (polytrophic compression) to 31 psig, it will increase the air temperature to 272.86 degrees F, with a resultant air density of 0.16838 pounds per cubic foot. Note: I am neglecting inefficiencies within the turbocharger’s compressor wheel. The actual air temperature will be warmer, however there will also be heat loss through the intake piping, and a whole lot of heat loss if there’s intercooling. . . Which is why I need to know if there’s intercooling on this engine.
A 16 liter 4-stroke engine at 1650 rpm will displace 7.7692 cubic feet per second. I’ll assume a 2-valve head, with a pumping volumetric efficiency of 70% at 1650 rpm – thus the engine is ingesting about 0.91572 pounds of air per second, at 1650 rpm.
The atmospheric air being sucked into the engine (14.7 psia at 70 degrees F) has an enthalpy of about 126.6 BTU per pound mass. The exhaust gas (350 degrees C, or 662 degrees F) will have an enthalpy of about 271.0 BTU per pound mass. Thus the net heat input into the exhaust gas is 144.4 BTU per pound mass. And with 0.91572 pounds of air per second flowing through the engine at 1650 rpm, you'll have 132.23 BTU per second entering the exhaust gas, or 476,030 BTU per hour entering the exhaust gas. This heat loss out the exhaust is equal to roughly 187 horsepower.
In the meantime, I will make some assumptions, and give you some numbers.
At sea level, on a 70 degree F day, air weighs about 0.07489 pounds per cubic foot. By compressing this air within a turbocharger’s compressor wheel (polytrophic compression) to 31 psig, it will increase the air temperature to 272.86 degrees F, with a resultant air density of 0.16838 pounds per cubic foot. Note: I am neglecting inefficiencies within the turbocharger’s compressor wheel. The actual air temperature will be warmer, however there will also be heat loss through the intake piping, and a whole lot of heat loss if there’s intercooling. . . Which is why I need to know if there’s intercooling on this engine.
A 16 liter 4-stroke engine at 1650 rpm will displace 7.7692 cubic feet per second. I’ll assume a 2-valve head, with a pumping volumetric efficiency of 70% at 1650 rpm – thus the engine is ingesting about 0.91572 pounds of air per second, at 1650 rpm.
The atmospheric air being sucked into the engine (14.7 psia at 70 degrees F) has an enthalpy of about 126.6 BTU per pound mass. The exhaust gas (350 degrees C, or 662 degrees F) will have an enthalpy of about 271.0 BTU per pound mass. Thus the net heat input into the exhaust gas is 144.4 BTU per pound mass. And with 0.91572 pounds of air per second flowing through the engine at 1650 rpm, you'll have 132.23 BTU per second entering the exhaust gas, or 476,030 BTU per hour entering the exhaust gas. This heat loss out the exhaust is equal to roughly 187 horsepower.
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To simplify what Entropy455 said, the two pieces of information you need are the mass flow and the entropy of the exhaust gas. If you wanted to split hairs, you'd also need to know the specific heat of the actual exhaust gas composition in calculating the entropy, but for practical purposes you can use that of air, since its 78% nitrogen anyway.
As dieselpilot suggested, the basic information may be available from the manufacturers data sheets.
As dieselpilot suggested, the basic information may be available from the manufacturers data sheets.
Very good explanation!
Wow that blew me away I think they are a 4 valve head but I think your numbers are close enough.its amazing what horsepower is lost through the exhaust gas.it is intercooled.what would happen if you cooled the intake air by means of a airconditioner.do you think that to much air entering the cylinder would cause damage or do you think there is not sufficient cooling to achieve any great result
Entropy455
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Intercooling increases air density upstream of the intake valve. This means that rpm for rpm, youll have a greater mass-flow-rate of air moving throughout the engine with intercooling - which means you can introduce more fuel per stroke, which equates to more net power per cubic inch. As with most things in life, there is a point of dimensioning returns with intercooling. Air conditioning compressors consume power, and any power returns at the crankshaft from AC-intercooling will likely fall short of the additional power requirements of driving the AC compressor (i.e. a net power loss).
You basically lose heat three ways heat loss into the air (radiator/coolant, oil cooler, intercooler, etc), heat loss out the exhaust (unavoidable by design), and heat that is converted into rotational power (the goal).
Keep in mind that the majority of heat dumped out of an intercooler was already preexisting within the air. I.E. squeezing the airs internal energy into a tighter space will drastically raise the airs temperature. Inefficiencies within the compressor wheel will add some additional heat. Nonetheless, the bulk of the temperature rise is from a change in the air's energy density, and not from the compressor flow-work.
Another interesting tidbit: The density of air (gasses) behaves opposite of liquids. I.E. colder air will have less viscosity than warmer air which is completely counterintuitive as liquids increase viscosity when they get colder.
You basically lose heat three ways heat loss into the air (radiator/coolant, oil cooler, intercooler, etc), heat loss out the exhaust (unavoidable by design), and heat that is converted into rotational power (the goal).
Keep in mind that the majority of heat dumped out of an intercooler was already preexisting within the air. I.E. squeezing the airs internal energy into a tighter space will drastically raise the airs temperature. Inefficiencies within the compressor wheel will add some additional heat. Nonetheless, the bulk of the temperature rise is from a change in the air's energy density, and not from the compressor flow-work.
Another interesting tidbit: The density of air (gasses) behaves opposite of liquids. I.E. colder air will have less viscosity than warmer air which is completely counterintuitive as liquids increase viscosity when they get colder.
Engine efficiency for engines of similar size and design doesn't vary much. If we follow the Scania example, we find it burns 104kg/hr at 500kW output. This is 1.234MW/hour in fuel. 339kW in the exhaust /1234kW= 25.6% of fuel heat energy is lost in the exhaust. This is at 124L per hour. So we could guess that 75L/h * .84kg/L = 63kg/h x 11.86kW/kg = 747kW * .25 = 187kW in the exhaust. This is a bit more than Entropy figures, but I also think volumteric efficency is greater than 70%.
Another interesting thing to see in the Scania spec sheet is air consumption of 40kg/min and exhaust flow of 41kg/min. The difference is the fuel. The air fuel ratio is 40:1 at full load. And from 1.234MW input / 500kW output, we see this engine is 40.5% efficient. You don't see diesels of 50% efficiency until the multi megawatt output types used in ships Sulzer, Wartsila.
Greg
Another interesting thing to see in the Scania spec sheet is air consumption of 40kg/min and exhaust flow of 41kg/min. The difference is the fuel. The air fuel ratio is 40:1 at full load. And from 1.234MW input / 500kW output, we see this engine is 40.5% efficient. You don't see diesels of 50% efficiency until the multi megawatt output types used in ships Sulzer, Wartsila.
Greg
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Entropy you mentioned that air is more viscous at higher temperatures is this why they have intake manifold heaters that are running radiator temp all the time.always thought it was stupid to heat the incoming air as we all work on cold air hot fuel and hot engine temps give the best power and efficiency. I know the v8 noyce Diesel engine was good for about 150 rpm more on a cold night and pulled a lot better too
Entropy455
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Air is preheated on carbureted gasoline engines to minimize fuel de-atomization. Modern fuel-injected gasoline engines are typically not preheated, as the injectors are sitting just upstream of the intake valves - and theres not enough time for fuel de-atomization, even with cold air. Also, modern automobile intakes are often plastic now, which would melt from an exhaust crossover. . . .
Air is preheated on diesel engines, primarily to initiate combustion during cold-starts. I see no need to preheat air otherwise on a diesel, except for maybe artic service. Supercharging and/or turbocharging will inherently heat the air, but we usually try to remove this heat.
The difference in air viscosity as a function of temperature is pretty negligible in the big picture of piston engine design. The biggest problem with internal combustion piston engines is the fact that the exhaust gas goes supersonic across the valve seats which is why engine exhaust is so darn loud. . . .
Air is preheated on diesel engines, primarily to initiate combustion during cold-starts. I see no need to preheat air otherwise on a diesel, except for maybe artic service. Supercharging and/or turbocharging will inherently heat the air, but we usually try to remove this heat.
The difference in air viscosity as a function of temperature is pretty negligible in the big picture of piston engine design. The biggest problem with internal combustion piston engines is the fact that the exhaust gas goes supersonic across the valve seats which is why engine exhaust is so darn loud. . . .
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Intercoolers are sometimes air to water . The function is the same to cool the incoming air charge even 250 is better than 500 degrees. Air to air intercooling is bulkier and more expensive. But can lower the temps another 100 degrees.
