Pratt & Whitney Pure Power Geared Turbofan Engine
Fuel-sipping jet
Pratt & Whitney Pure Power Geared Turbofan Engine
Pratt & Whitney
In most jet engines (more properly called turbofans), the fan that pulls air into the engine is directly linked to the compressor that squeezes that air down for combustion, so they have to turn at the same rate. By placing gears between the compressor and the fan, decoupling the two, the Pure Power engine allows for a more efficient arrangement: a big, slow fan shoving air into a small, fast turbine. The result is a shorter, lighter engine that can produce the same amount of power as a larger conventional turbofan, while burning 12 to 15 percent less fuel and emitting 35 percent less carbon dioxide. Pratt & Whitney finished ground- and air-testing of the engine this year, and the first of them will go on the Bombardier C-Series jet starting in 2013.
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The 35 percent reduction in carbon dioxide emissions above is incorrect. Carbon dioxide emissions are linearly related to the amount of fuel burned. A 15 percent reduction in fuel burned results in a 15 percent reduction in carbon dioxide emissions.
What about CO and C? You can reduce CO2 beyond fuel comsumption if you reduce CO, C and unburned fuel.
That is incorrect. You can have an offset ration of consumption versus emissions if the efficiency of the combustion is increased, as in the case of this engine.
changes in CO2 and fuel use are closely coupled so CH3NO2 is incorrect - modern commercial engines have very small un-burned hydrocarbons so a claim that an increase in combustion efficiency can greatly improved is incorrect. The engines do get efficiency improvements in temperatures, cooling air management, ....
gbrucegolden,
so a decrease in combustion temperature would not decrese emissions and a decrease in rotational mass will not increase fuel efficiency? I disagree. As far as the statement about small unburned hydrocarbons in modern engines, again, I disagree.
elegantpie is correct.! simple school chemistry.! For the amount of HC (hydrocarbon) burnt, you get an equal amount of CO2 and H2O. UNLESS you are not burning it properly, (stoichiometric ratio is off) then you get CO and unburnt fuel in exhaust.
If the engine is not converting all the fuel into CO2 and H2O, then I don't want that engine.
These engines don't run stoich, they are ox-rich because the temps at stoich would melt the turbines. By altering the temp at which combustion occurs we can alter the mixture of exhaust gases. There is no good reason a linear relationship holds as there are temperature differences in the combustor that would result in different exhaust mixtures also. So CO2 varies with amount of fuel (more precisely Fuel-air ratio) but also with temperature. The layout of the combustor is also tailored to provide the right temperatures and control emissions (as a good example google staged combustion).
For case A and case B, the thrust produced is the same.
And, case B is using 85% the fuel of case A.
Therefore, the amount of carbon going in and coming out of the combustion chamber in case B is exactly 85% of case A. The only question is what form is this carbon; i.e. CO2, CO, or the original JP5? This primarily depends on the combustion temp and pressure, and both of these are material limited in the quest for higher efficiency. But, as the efficiency goes up, the JP5 component in the exhaust goes down and the CO2+CO goes up, and both are pollutants. Thus, unless they reduced the efficiency of the combustion, the original "35% reduction" statement is incorrect. Is it possible they reduced the efficiency? Yes, since the efficiency of the fan is so substantially improved, it is possible they reduced the efficiency of the combustion chamber (but unlikely).