Kerosene, Jet Fuel, Lockheed Constellation, Boeing 707, Boeing 747-400, Newton’s Third Law of Motion, Turbojet and Fan Jet

Posted by PITHOCRATES - October 3rd, 2012

Technology 101

The only way to make Flying Available to the General Public is to put as many People as Possible on an Airplane

Refined petroleum products have made our lives better.  We have gasoline to drive wherever we want.  We have diesel fuel to transport things on ships and trains like petroleum oil, iron ore, coal, food, medicine, smartphones, coffee, tea, wine, scotch whisky, bourbon whiskey, beer, fresh fish, sushi, etc.  Pretty much everything we buy at a store or a restaurant got there on something powered by diesel fuel.  And sometimes kerosene.  If it must travel fast.  And if it does then it finds itself on a jet aircraft.

Today aviation has shrunk the world.  We can order a new smartphone sitting on a shelf in California and have it the next day in New York.  We can even travel to distant countries.  Some in the time of a typical working day.  Some a half a day or longer.  When but a 100 years earlier it took a couple of weeks to cross the Atlantic Ocean.  While 200 years ago it took a couple of months.  We can travel anywhere.  And get there quickly.  Thanks to the jumbo jet.  And not just the super-rich.  Pretty much anyone today can afford to buy a plane ticket to travel anywhere in the world.  And one thing makes this possible.  The jet engine.

Airplanes are expensive.  So are airports, air traffic control and jet fuel.  Airlines pay for all of these costs one passenger at a time.  Their largest cost is their fuel cost.  The longer the flight the greater the cost.  So the only way to make flying available to the general public is to put as many people as possible on an airplane.  Dividing the total flying cost by the number of passengers on the airplane.  This is why we fly on jumbo jets for these longer flights.  Because there are more people to split the total costs.  Lowering the cost per ticket.  Before the jet engine, though, it was a different story.

The Boeing 747-400 can take up to 660 Passengers some 7,260 Miles at a Speed of 567 MPH

One of the last intercontinental propeller-driven airplanes was the Lockheed Constellation.  A plane with four (4) Wright R-3350-DA3 Turbo Compound 18-cylinder supercharged radial engines putting out 3,250 horsepower each.  Which is a lot considering today’s typical 6-cyclinder automobile engine is lucky to get 300 horsepower.  No, the horsepower of one of these engines is about what one modern diesel-electric locomotive produces.  So these are big engines.  With a total power equal to about four locomotives lashed up.  Which is a lot of power.  And what does that power allow the Constellation do?  Not much by today’s standards.

In its day the Lockheed Constellation was a technological wonder.  It could take up to 109 passengers some 5,500 miles at a speed of 340 mph.  No bus or train could match this.  Not to mention it could fly over the water.  Then came the age of the jet.  The Boeing 707 being the first largely successful commercial jetliner.  Which could take up to 189 passengers some 6,160 miles at a speed of 607 mph.  That’s 73.4% more passengers, a 78.5% faster speed and a 14.1% longer range.  Which is an incredible improvement over the Constellation.  But nothing compared to the Boeing 747-400.  Which can take up to 660 passengers (506% more than the Constellation and 249% more than the 707) some 7,260 miles at a speed of 567 mph.

Now remember, fuel is the greatest cost of aviation.  So let’s assume that a intercontinental flight costs a total of $75,000 for each plane flying the same route.  Dividing that cost by the number of passengers you get a ticket price of approximately $688, $397 and $114 for the Constellation, the 707 and the 747-400, respectively.  So you can see the advantage of packing in as many passengers as possible into an airplane to lower the cost of flying.  Which is why the jumbo jets fly the longest routes that consume the most fuel.  And why we no longer fly propeller-driven aircraft except on short routes to airports with short runways.  These engines just don’t have the power to get a plane off the ground with enough people to reduce the cost of flying to a price most people could afford.  Only the jet engine has that kind of power.

The Fan Jet is basically a Turbojet with a Large Fan in front of the Compressor

Newton’s Third Law of Motion states that for every action there is an equal and opposite reaction.  Think of a balloon you just blew up and are holding closed.  If you release your hold air will exit the balloon in one direction.  And the balloon will move in the opposite direction.  This is how a jet engine moves an aircraft.  Hot exhaust gases exit the engine in one direction.  Pushing the jet engine in the opposite direction.  And because the jet engines move the plane moves.  With the force of the jet engines transferred via their connection points to the aircraft.  The greater the speed of the gas exiting the jet the faster it will push a plane forward.

The jet engine gets that power from the continuous cycle of the jet engine.  Air enters one end, gets compressed, enters a combustion chamber, mixes with fuel (kerosene), ignites, expands rapidly and exits the other end.  The hot (3,632 degree Fahrenheit) and expanding gases pass through and spin a turbine.  Then exit the engine.  The turbine is connected to the compressor at the front of the engine.  So the exhaust gases spin the compressor that sucks air into the engine.  As the air passes through the compressor it compresses and heats up.  Then it enters the combustion chamber and joins fuel that is injected and burned continuously.  Sort of like pouring gas on a burning fire.  Only enormous amounts of compressed air and kerosene are poured onto a burning fire.  As this air-fuel mixture burns it rapidly expands.  And exits the combustion chamber faster than the air entered it.  And shoots a hot stream of jet gas out the tail pipe.  Which produces the loud noise of these turbojets.  This fast jet of air cuts through the surrounding air.  Resulting in a shear effect.  Which the next generation of jet engines, the fan jet, greatly reduces.

The fan jet is basically a turbojet with one additional feature.  A large fan in front of the compressor.  These are the big engines you see on the jumbo jets.  They add another turbine inside the jet that spins the fan at the front of the engine.  Which feeds some air into the compressor of what is basically a turbojet.  But a lot of the air this fan sucks in bypasses the turbojet core.  And blows directly out the back of the fan at high speed.  In fact, this bypass air provides about 75% of the total thrust of the fan jet.  Acting more like a propeller than a jet.  And as an added benefit this bypass air surrounds the faster exhaust of the jet thereby lessening the shear effect.  Making these larger engines pretty quiet.  In fact a DC-9, an MD-80, a 707 or a 727 with standard turbojets are much louder than a 747 with 4 fan jets at full power.  They’re quieter.  And they can push a lot more people through the air at incredible speeds over great distances at a reasonable price per passenger than any other aircraft engine.

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Generator, Current, Voltage, Diesel Electric Locomotive, Traction Motors, Head-End Power, Jet, Refined Petroleum and Plug-in Hybrid

Posted by PITHOCRATES - June 6th, 2012

Technology 101

When the Engineer advances the Throttle to ‘Run 1’ there is a Surge of Current into the Traction Motors

Once when my father suffered a power outage at his home I helped him hook up his backup generator.  This was the first time he used it.  He had sized it to be large enough to run the air conditioner as Mom had health issues and didn’t breathe well in hot and humid weather.  This outage was in the middle of a hot, sweltering summer.  So they were eager to get the air conditioner running again.  Only one problem.  Although the generator was large enough to run the air conditioner, it was not large enough to start it.  The starting in-rush of current was too much for the generator.  The current surged and the voltage dropped as the generator was pushed beyond its operating limit.  Suffice it to say Mom suffered during that power outage.

Getting a diesel-electric locomotive moving is very similar.  The massive diesel engine turns a generator.  When the engineer advances the throttle to ‘Run 1’ (the first notch) there is a surge of current into the traction motors.  And a drop in voltage.  As the current moves through the rotor windings in the traction motors it creates an electrical field that fights with the stator electrical field.  Creating a tremendous amount of torque.  Which slowly begins to turn the wheels.  As the wheels begin to rotate less torque is required and the current decreases and voltage increases.  Then the engineer advances the throttle to ‘Run 2’ and the current to the traction motors increases again.  And the voltage falls again.  Until the train picks up more speed.  Then the current falls and the voltage rises.  And so on until the engineer advances the throttle all the way to ‘Run 8’ and the train is running at speed. 

The actual speed is controlled by the RPMs of the diesel engine and fuel flow to the cylinders. Which is what the engineer is doing by advancing the throttle.  In a passenger train there are additional power needs for the passenger cars.  Heating, cooling, lights, etc.  The locomotive typically provides this Head-End Power (HEP).  The General Electric Genesis Series I locomotive (the aerodynamic locomotive engines on the majority of Amtrak’s trains), for example, has a maximum of 800 kilowatts of HEP available.  But there is a tradeoff in traction power that moves the train towards its destination.  With a full HEP load a 4,250 horsepower rated engine can only produce 2,525 horsepower of traction power.  Or a decrease of about 41% in traction horsepower due to the heating, cooling, lighting, etc., requirements of the passenger cars.  But because passenger cars are so light they can still pull many of them with one engine.  Unlike their freight counterparts.  Where it can take a lashup of three engines or more to move a heavy freight train to its destination.  Without any HEP sapping traction horsepower.

There is so much Energy available in Refined Petroleum that we can carry Small Amounts that take us Great Distances

The largest cost of flying a passenger jet is jet fuel.  That’s why they make planes out of aluminum.  To make them light.  Airbus and Boeing are using ever more composite materials in their latest planes to reduce the weight further still.  New engine designs improve fuel economy.  Advances in engine design allow bigger and more powerful engines.  So 2 engines can do the work it took 4 engines to do a decade or more ago.  Fewer engines mean less weight.  And less fuel.  Making the plane lighter and more fuel efficient.  They measure all cargo and count people to determine the total weight of plane, cargo, passengers and fuel.  So the pilot can calculate the minimum amount of fuel to carry.  For the less fuel they carry the lighter the plane and the more fuel efficient it is.   During times of high fuel costs airlines charge extra for every extra pound you bring aboard.  To either dissuade you from bringing a lot of extra dead weight aboard.  Or to help pay the fuel cost for the extra weight when they can’t dissuade you.

It’s similar with cars.  To meet strict CAFE standards manufacturers have been aggressively trying to reduce the weight of their vehicles.  Using front-wheel drive on cars saved the excess weight of a drive shaft.  Unibody construction removed the heavy frame.  Aerodynamic designs reduced wind resistance.  Use of composite materials instead of metal reduced weight.  Shrinking the size of cars made them lighter.  Controlling the engine by a computer increased engine efficiencies and improved fuel economy.  Everywhere manufacturers can they have reduced the weight of cars and improved the efficiencies of the engine.  While still providing the creature comforts we enjoy in a car.  In particular heating and air conditioning.  All the while driving great distances on a weekend getaway to an amusement park.  Or a drive across the country on a summer vacation.  Or on a winter ski trip.

This is something trains, planes and automobiles share.  The ability to take you great distances in comfort.  And what makes this all possible?  One thing.  Refined petroleum.  There is so much energy available in refined petroleum that we can carry small amounts of it in our trains, planes and automobiles that will take us great distances.  Planes can fly halfway across the planet on one fill-up.  Trains can travel across numerous states on one fill-up.  A car can drive up to 6 hours or more doing 70 MPH on the interstate on one fill-up.  And keep you warm while doing it in the winter.  And cool in the summer.  For the engine cooling system transfers the wasted heat of the internal combustion engine to a heating core inside the passenger compartment to heat the car.  And another belt slung around an engine pulley drives an air conditioner compressor under the hood to cool the passenger compartment.  Thanks to that abundant energy in refined petroleum creating all the power under the hood we need.

The Opportunity Cost of the Plug-in Hybrid is giving up what the Car Originally gave us – Freedom 

And then there’s the plug-in hybrid car.  That shares some things in common with the train, plane and (gasoline-powered) automobile.  Only it doesn’t do anything as well.  Primarily because of the limited range of the battery.  Electric traction motors draw a lot of current.  But a battery’s storage capacity is limited.  Some batteries offer only about 20-30 miles of driving distance on a charge.  Which is great if you use a car for very, very short commutes.  But as few do manufacturers add a backup gasoline engine so the car can go almost as far as a gasoline-powered car.  It probably could go as far if it wasn’t for that heavy battery and generator it was dragging around with it.

This is but one of many tradeoffs required in a plug-in hybrid car.  Most of these cars are tiny to make them as light as possible.  For the lighter the car is the less current it takes to get it moving.  But adding a backup gasoline engine and generator only makes the car heavier.  Thus reducing its electric range.  Making it more like a conventional car for a trip longer than 20-30 miles.  Only one that gets a poorer fuel economy.  Because of the extra weight of the battery and generator.  Manufacturers have even addressed this problem by reducing the range of the car.  If people don’t drive more than 10 miles on a typical trip they don’t need such a large battery.  Which is ideal if you use your car to go no further than you normally walk.  A smaller battery means less weight due to the lesser storage capacity required to travel that lesser range.  Another tradeoff is the heating and cooling of the car.  Without a gasoline engine on all of the time these cars have to use electric heat.  And an electric motor to drive the air conditioner compressor.  (Some heating and cooling systems will operate when the car is plugged in to conserve battery charge for the initial climate adjustment).  So in the heat of summer and the cold of winter you can scratch off another 20% of your electric range (bringing that 20 miles down to 16 miles).  Not as bad as on a passenger locomotive.  But with its large tanks of diesel fuel that train can still take you across the country.

The opportunity cost of the plug-in hybrid is giving up what the car originally gave us.  Freedom.  To get out on the open road just to see where it would take us.  For if you drive a long commute or like to take long trips your hybrid is just going to be using the backup gasoline engine for most of that driving.  While dragging around a lot of excess weight.  To make up for some lost fuel economy some manufacturers use a gasoline engine with high compression.  Unfortunately, high compression engines require the more expensive premium (higher octane) gasoline.  Which costs more at the pump.  There eventually comes the point we should ask ourselves why bother?  Wouldn’t life and driving be so much simpler with a gasoline-powered car?  Get fuel economy with a range of over 300 miles?  Guess it all depends on what’s more important.  Being sensible.  Or showing others that you’re saving the planet.

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