Transportation Technologies

 

Transportation Technologies Transportation is a function of: Transportation is a function of: Historical Technologies Current Technologies Challenges with Future Technologies Why is it difficult to make transportation sustainable? Freight Transportation and Free Ranging Forced Induction Future Technologies Plug-In Hybrid Electric Vehicles (PHEV) Battery Electric Vehicles (BEV) Fuel cell vehicles: Compressed air Vehicles: Vehicles with Regenerative breaking: Solar electric vehicles: Efficiencies Bicycles Explore your transportation energy consumption: References

 

Transportation is a function of:

 

 

 

Figure 1:

 

Worldwide, the transportation sector accounted for approximately one-fourth of the total end-use energy consumption value of 426 EJ (403 quads) in 2003. In the United States alone, in the year the transportation sector accounted for 28.5 EJ (27.0 quads), which constitutes 27.5% of the total U.S. energy end-use budget of 103.7 EJ (98.3 quads), or 6.5% of the world total. To put this values in context, the U.S. transportation energy consumption rate is equivalent to 9 billion 100-W lightbulbs burning continuously 24h/day, 7 days a week, all year long, or 30 lightbulbs for every one of the United State's approximate population of 300 million people. The world transportation energy consumption figure is equivalent to 36 billion lightbulbs, or 6 lightbulbs per person. 

 

  

 

Transportation is a function of:



Historical Technologies

• 3500 BC: Fixed wheels on carts are invented
• 2000 BC: Horses are domesticated for transportation use
• 1492: Leondard DaVinci ponders flying machines
• 1620: Cornelius Drebbel invents first human oar powered submersible
• 1800: Richard Trevithick introduces steam engines that can be used with high-pressure steam and for transportation systems

 

 

Current Technologies

 

• Gasoline-powered motor vehicle
• Diesel-powered motor vehicle
• Jet fuel-powered airplanes
• Diesel-electric trains
• Food-powered walking, biking, etc.

 

Challenges with Future Technologies

 

Transportation energy technologies that replace the use of petroleum for transportation as currently practiced must (1) be based on a more abundant supply of energy and (2) avoid permanently increasing the concentration of carbon in the atmosphere to avert climate change.

 

Future Technologies:

 

• Battery-electric
• Hydrogen fueled
• Sustainable hydrocarbons                                                      
• Alternative onboard energy storage 
• No motor vehicles                                                     

 

      

Although there might appear to be a wide range of technologies competing to play the role of replacing the use of petroleum for transportation as currently practiced, each can in its essence be reduced to one of the five "endpoint technologies" that meets the objectives of abundant supply and protecting the climate.

 

 

All five endpoint technologies share a few common characteristics:

 

• They all present substantial technical, organizational, and financial challenges.
• Wether or not the endpoint technologies require the introduction of new vehicle technologies or use existing ones, they all require infrastructure to transform existing energy sources into a form that can be stored on a vehicle, and others require infrastructure to process CO₂ already in the atmosphere, or the sequester CO₂ that is a by-product of conversion to the energy currency used onboard the vehicle.
• The endpoint technologies are not mutually exclusive. It is possible that one will eventually become dominant, and it is also possible that multiple ones will each claim some niche in meeting transportation energy demand. An analogy could be made with today's situation, where most surface transportation (road, rail, ship) is propelled by petroleum-fueled internal combustion engines, but a minority of rail service uses electricity supplied from outside the vehicle.  

 

Why is it difficult to make transportation sustainable?

 

• Transportation is highly dependent on fossil fuels!
• Fossil fuels are liquid based, which would be hard to replace.

               We use liquid fuels because they have a high energy density, great energy storage, and they are portable. 

• Transportation requires energy storage because we move our energy source around with us.  

 

Competition between Emerging and Incumbent Technologies:

In considering the transition to alternative transportation technologies, the influence of the starting point of today and the existing worldwide fleet of motor vehicles, aircraft, and other consumers of transportation energy from petroleum, and the infrastructure that supplies this energy must be recognized. While alternative pathways are desirable in the long run, today they must be introduced in the context of a mature petroleum-based system that is the "incumbent" technology, and the expectations in terms of price, reliability, performance, and so on, which this system has created in consumers. 

 

 

Freight

 

Freight is also important to the future of sustainable transportation.  Currently, large trucks dominate the freight transportation market even though other methods are more fuel efficient and, therefore, less carbon intensive.

 

In the 1910's, the train used coal-driven steam engines to travel from N.Y. to the Midwest.

Currently, Mississippi has a great freight movement.

 

Table 1: Freight movement by mode

Millions of tons of freight moved by mode
Trucks	Rail	Water	Air	Intermodal	Pipeline
12,896	2,030	689	14	1,505	4,091

 

 

Figure 2: Tonnage on Highways, Railroads and Inland Waterways: 2002

 

 

*Refer to Transportation Systems for more information about systems and modes of transportation.

 

Transportation and Free Ranging

 

• Heat Engines
• Diesel, gasoline, natural gas, jet fuel
• Biofuels
• Improve efficiency
• Electric Vehicles
• Can we do this?
• Some challenges: 
• Battery Technology
• Where is the electricity coming from?
• Hydrogen Vehicles
• Can we do this?
• Some challenges: 
• Transportation is 25% of all energy consumption, this is not possible but it would cost a lot.
• Biomass
• Can we do this? 
• Some challenges:

                              Deriving all heat engine fuels from biomass; just not enough biomass to do that. 

                              Can't meet the demand.

 

Figure 3: Fuel Cycle CO₂ for different vehicle options

 

• Heat Engine Types and Cycles
• External Combustion Engine
• Steam Engine, runs off of the Rankine Cycle
• Rankine Cycle
• As shown in the Steam Engine diagram below, water enters the pump as a saturated liquid (no vapor) and is compressed isentropically (no change in entropy) to the operating pressure of the boiler.  The boiler is heated by burning combustible fuel, creating exhaust and releasing it.  After being compressed, the water enters the boiler, is heated, and leaves as a superheated vapor.  The superheated vapor enters the turbine, where it expands isentropically and produces work by rotating the shaft connected to a generator that produces electricity or a drive shaft (Cengel and Boles, 567-568). 

 

 

 

 

Figure 4: Steam Engine

 

• Internal Combustion Engines (ICE's)
• Gas Turbine  
• Runs off of Brayton Cycle
• As shown in the Brayton Cycle diagram below, fresh air at ambient conditions is drawn into the compressor, where its temperature and pressure are increased.  The high-pressure air flows into the combustion chamber, where the fuel is burned at constant pressure.  The resulting high-temperature gases then enter the turbine, where they expand to atmospheric pressure while producing power.  The exhaust gases then leave the turbine and are released to the outside (Cengel and Boles, 517).
• With regeneration, gas cycle is more efficient than steam engine

 

 

 

 

Figure 5: Gas Turbine Engine

 

 

 

Figure 6: Gas Turbine Engine runs off of the Brayton Cycle

 

• Reciprocating Engines - Otto Cylce (Spark ignition)
• Nikolaus Otto, a German engineer, created the first one in 1876
• Sold more than 30,000 in ten years
• In 1887, Gottlieb Daimler attached an Otto (reciprocating) engine to a bike
• At the same time, Karl Benz built a 3-wheeled car with the Otto engine
• In 1898, the first Mercedes Benz was built
• In 1899, David Dunbar Buick builds the first Buick.  http://www.buickclub.org/Misc/history.htm 
• In 1913, Henry Ford installed the first assembly line
• Ford was selling a 1,000,000 cars per year 10 years later
• Otto Cycle
• As shown in the Otto cycle diagram below, initially, both the intake and exhaust valves are closed, and the piston is at its lowest position.  During the compression stroke, the piston moves upward, compressing the air-fuel mixture.  Right before the piston reaches its highest position, the spark plug fires and the mixture ignites, increasing the pressure and temperature of the system.  The high-pressure gases force the piston down, which in turn forces the crankshaft to rotate, producing a useful work output during the expansion or power stroke.  At the end of the power stroke, the piston moves upward, purging the exhaust gases through the exhaust valve.  Finally, the piston moves downward, drawing in fresh air-fuel mixture through the intake valve (Cengel and Boles, 505). 
• Actual efficiency of Otto cycle is dictated by the compression ratio
• Refer to links for more information about:
• Animation of Otto cycle:  http://www.animatedengines.com/otto.shtml

 

 

 

Figure 7: Spark Ignition Engines-Run off of the Otto Cycle

 

 

 

 

Figure 8: Spark Ignition Engine

 

• Reciprocating Engines - Diesel Cycle (Compression ignition)
• Rudolf Diesel, a German engineer, produced the first one in 1898
• Became a preferred engine of ships
• In 1926, 5% of ships had them and 10 years later, 20% had them
• First diesel lorry (commercial truck) appeared in 1931
• By 1934, almost all trucks and buses in UK had diesel
• Diesel Cycle
• As shown in the Diesel cycle diagram below, initially, the piston is at its lowest point.  During the compression stroke, the piston moves upward, compressing just the air inside the piston chamber.  As the piston approaches its highest position, the fuel injection process starts and continues during the first part of the power stroke.  The power stroke occurs when the piston is at its highest position and the fuel that is injected reaches its autoignition temperature.  The fuel ignites, increasing the pressure and temperature of the system.  The high-pressure gases force the piston down, which in turn forces the crankshaft to rotate, producing a useful work output.  At the end of the power stroke, the piston moves upward, purging the exhaust gases through the exhaust valve.  Finally, the piston moves downward, drawing in fresh air through the intake valve (Cengel and Boles, 510).
• Diesel engine has highest thermal efficiency of  internal combustion engines
• Diesel engine is louder than gasoline
• Refer to link for more information about:  
• Diesel engine:  http://en.wikipedia.org/wiki/Diesel_engine
• Animation of Diesel engine:  http://www.animatedengines.com/diesel.shtml

 

 

 

 

Figure 9: Compression Ignition Engines-Run off of the Diesel Cycle

 

 

Figure 10: Compression Ignition Engine

 

• Detailed article on the Otto vs. Diesel Engines: http://www.bankspower.com/techarticles/show/26-Understanding-Todays-Diesel  

 

• Stirling Engine
• Invented and patented by Robert Sterling in 1816
• Has mostly been used for low-power domestic applications
• Stirling Cycle
• As shown in the pictures below, the Stirling cycle involves constant expansion (heat-addition from the external source), constant regeneration (internal heat transfer from the working fluid to the regenerator), constant compression (heat rejection to the external sink) and constant regeneration (internal heat transfer from the regenerator back to the working fluid) of a working fluid that is normally air or some other gas (Cengel and Boles, 515-516).
•  Theoretically the most efficient type of closed cycle heat engine
• Refer to link for more information about:  
• Animation of Sterling engine:  http://www.animatedengines.com/stirling.shtml                                                                                 

 

 

 

Figure 11: Stirling Engine and Cycle

 

 

 

Figure 12: Stirling Engine Cycles

 

     For more information about heat engines visit this site Electropeadia 

 

• Hybrid Motor Vehicles

 

• Combination of electric and gasoline engine
• Configuration can be in parallel or series
• Could be configured to regenerative braking
• Design optimizes ICE at the expense of power
• Uses battery to add power when high power is demanded
• Keep combustion conditions at optimal levels for minimal pollutant emissions
• Runs off of the Atkinson Cycle
• In Prius cars: The Atkinson cycle could be from 10 to 15 times more efficient because of optimal compression and expansion
• How is ICE optimized?
• Variable Valve Timing with Intelligence
• Intake valve stays open for a portion of the compression stroke
• Atkinson Cycle
• As shown in the Atkinson Cycle below, it is very similar to the Otto cycle.  The only difference between the Atkinson and the Otto cycle is that the intake valve is left open for part of the compression stroke.  This causes the effective compression ratio to be reduced, but the expansion ratio remains the same.  So when the fuel combusts and forces the piston down, the greater expansion ratio allows more energy to be converted from heat to useful mechanical energy meaning the engine is more efficient.



• Refer to link for more information about:
• Animation of Atkinson cycle:  http://www.animatedengines.com/atkinson.shtml

 

Forced Induction

 

In addition to the current technology available, several automakers have been experimenting with forced induction, effectively increasing the engine's power output when compared to a naturally aspirated engine of the same displacement. While there are many variations of forced induction currently being driven, they all stem from either a turbocharger or a supercharger. The following information briefly explains the advantages/disadvantages associated with either forced induction technology while the links may be used for a more detailed explanation.

 

• Turbocharger
• Uses the exhaust gas to spin a turbine blade connected by a shaft to the compressor blade which moves air into the combustion chamber. As the exhaust gas velocity increases, each turbine moves faster, forcing more air into the engine, therefore producing more power.
• Detailed Descriptions: How Turbochargers Work, BorgWarner Turbocharger
• Detailed Animation:  Ford EcoBoost Turbocharger
• Advantages
• May provide similar power gains when compared to increased displacement
• Gas mileage unchanged when off the throttle. The vehicle basically performs like a naturally aspirated engine when out of "boost."
• Small/Lightweight design allows for use in smaller vehicles
• Increased performance at higher altitudes due to increased pressure
• Disadvantages
• Increased load on the engine requires more maintenance
• Costly replacement+labor in the event of failure
• Less responsive, noticeable "lag" upon pressing the gas pedal as the velocity of the exhaust gases must increase
• Requires high grade fuel to avoid engine knock (detonation of the air/gas mixture before the spark plug ignites) which can damage the internal components of the engine
• May require intercooling in hot climates to avoid engine knock

 

• Supercharger
• Essentially the same concept as a turbocharger only instead of using the exhaust gases to spin the turbine, a supercharger utilizes a mechanically driven gear or belt to spin the compressor turbine which forces excess air into the engine.
• Detailed Description: How Superchargers Work
• Detailed Animation: Gear Train, Air System Fundamentals, Chevrolet Corvette ZR1 Engine
• Advantages
• Provides similar gains to those of a turbocharger
• Because the compressor is being driven by the engine and not the exhaust gas, there is no associated "lag" with a supercharger (instant power similar to large V8)
• Disadvantages
• A supercharger creates more strain on all of the engine components than a turbocharger simply because it is being driven by the engine itself
• Even more costly than a turbocharger replacement if broken. In addition, there are many more components associated with a supercharger as there is a small gear box to drive the compressor faster than the spinning crankshaft of the engine.
• Requires high grade fuel to avoid engine knock
• Also may require intercooling to avoid knock

 

Forced induction has allowed many automakers to use smaller displacement engines (1.4-2.2L) for impressive gas mileage while still being able to supply enough power to the wheels via the turbocharger/supercharger. 

 

Future Technologies

 

With the present environmental concerns, transportation fuel prices & considering its future demand; the cars of the future are more inclined towards higher fuel economy and alternative/green technology. Few of the technologies that are presently being explored are listed below,

• Battery-electric 
• Hydrogen fueled
• Solar Electric Vehicles
• Vehicles with Regenerative breaking
• Compressed air Vehicles 
• Sustainable hydrocarbons (such as ethanol and biodiesel)
• Alternative onboard energy storage
• No motor vehicles

 

Adopting any of these technologies may require changes in our definition of cars and social behavior in general.  At the very least, implementing any of these technologies or approaches will require a massive change in our transportation infrastructure (with the possible exception of sustainable biofuels, which is why there is so much interest in this option). This is in contrast to sustainable electricity and heat systems, which will be implemented on the generation end and do not require such drastic and evident changes on the consumer end. 

 

For example,  there are currently about 115,000 gas stations in the United States, versus a handful of electric vehicle charging stations or hydrogen stations. And although almost any vehicle can be filled with gasoline or diesel fuel in a few minutes, charging an electric vehicle can take anywhere from 30 minutes to several hours.

 

Plug-In Hybrid Electric Vehicles (PHEV)

• PHEVs are similar to Hybrid Electric Vehicles (HEVs) but have more battery storage and can be charged by plugging them into an electrical outlet. This allows PHEVs to drive short distances using only electricity, dramatically increasing overall fuel economy.
• RASEI (Renewable and Sustainable Energy Institute at CU) and Xcel Energy's SmartGridCity team up with 10 new Prius PHEVs for testing as shown in picture below
• 12-mile electric-only range
• Toyota expects to begin producing the Prius PHEV commercially in 2012. 
• The Chevy Volt PHEV was released in late 2010 in several regional markets.
• Because PHEVs can run on gasoline and can be plugged into normal electrical outlets, they do not require big changes in infrastructure to deploy.
• On the other hand, PHEVs charge slowly from standard outlets, and like BEVs, require special charging stations to charge quickly.

 

Figure 13: Prius PHEV

 

 

Battery Electric Vehicles (BEV)

• Battery electric vehicles do not have internal combustion engines and run only on electricity, using batteries to store energy.
• Several manufacturers have introduced or are developing BEVs.
• Tesla Roadster (available now)
• Tesla Model S (available 2012)
• GEMe2
• Nissan LEAF (available now) 
• Toyota iQ (available in Europe) 
• BMW Mega-City (available 2013)
• Why are so many BEVs being developed?
• California will shortly require lower greenhouse gas emissions from vehicles under its AB32 climate change law.
• It has also passed laws mandating a certain number of zero emission vehicles (ZEVs) be available by 2012, and BEVs qualify.
• Infrastructure
• Very few BEV charging stations exist in the US.
• The Department of Energy's EV Project is a partnership with many companies including GM, Nissan, and Ecotality to create a network of charging stations in six states, plus Washington, DC, and subsidize the deployment of PHEVs and BEVs.
• 14,560 charging stations
• 310 fast charging stations
• 5,700 Nissan Leaf cars
• 2,600 Chevrolet Volt cars
• Efficiency
• BEVs are more efficient at converting energy into useful work than standard vehicles, or even HEVs.
• The Tesla Roadster can travel 1.14 km/MJ, versus 0.556 km/MJ for a Prius or 0.478 km/MJ for a Volkswagen Jetta Diesel.
• Electricity Supply
• BEVs don't produce direct emissions, but if they are charged with electricity generated by coal or natural gas, they are responsible for indirect emissions.
• For BEVs to be truly clean, they need to be powered by renewable energy.
• But to convert 10% of the nation's vehicles to BEVs and power them completely with wind would require about 46,000 MW of new wind generation, more than double our current wind capacity.

 

• Note: BEV Mileage is better at higher altitude and warmer temperatures

 

Fuel cell vehicles:

• Fuel cell vehicles run on hydrogen instead of gasoline.
• The main benefits of such vehicles is they have zero emissions & they reduce our dependence on oil
• The major challenges that in the road to large scale commercialization of such vehicles are the vehicle cost, the large size of the hydrogen storage tank, supply of hydrogen to consumers & safety concerns.
• The Fuel economy of such vehicle is around 60 miles/kg of hydrogen
• The plant to wheel efficiency is in the range of 17 to 22 %

 

 

     Fig. 14: Fuel cell vehicle & its components.

 

Compressed air Vehicles:

• In case of a compressed air vehicle the motor is powered by compressed air.
• The compressed air is stored in storage tank at a pressure as high as 300 bar.
• Such Vehicles have zero emissions
• The main advantages of such vehicle are: they would be cheap because of less number of parts, refueling is easy.
• The efficiency of such vehicles are in the range of 14 – 20%

 

Fig. 15: Working of a compressed air engine. 

 

Vehicles with Regenerative breaking:

• In case of regenerative braking the energy that is lost during breaking of a vehicle is transformed to useful energy by converting it into electricity & storing the same in batteries.
• This system has been in use for a long time in electric locomotives.
• The other forms of energy storage options that are being explored are flywheels, capacitors & compressed air.

 

Fig. 16: Regenerative Breaking Mechanism.

 

Solar electric vehicles:

• The solar electric vehicles are similar to electric vehicle but with PV cells installed on them to harness solar energy to charge the batteries.
• The main limitations of such vehicles are the capital cost associated with the PV modules & the life time of the PV module, since their performance deteriorates with time.
• The 2010 Toyota Prius model will be having an option to mount solar panels on the roof, which will power a ventilation system to help provide cooling while parked.

  

Fig. 17: Solar Prius 

Efficiencies

 

How you select a vehicle is an important decision.  However, it can be hard to decide which type of vehicle is right for you and what the benefits are.  The US Department of Energy has put together a basic website that will give you information about the fuel efficiency of your current car or a car you are interested in buying.  (http://www.fueleconomy.gov/feg/findacar.htm)  Here you can find information about:

 

• Estimated EPA MPG
• Fuel Economics
• Energy Impact Scores
• Estimated Carbon Footprint
• Air Pollution Score 

 

 

 

 

Table 2: Different types of efficiencies for different types of vehicles 

 

 

Figure 18: Efficiencies as Tesla sees it

 

 

Bicycles

Don't forget, there is one other form of transportation that is rarely mentioned in engineering classes but there is a great deal of science that goes into the making and functionality of a bicycle.  Bicycles have one very distinct advantage over motor vehicles.  They don't weight much so there isn't a lot of losses due to transporting the bicycle itself.  However, biking is not necessarily a net zero activity.  It still takes energy to move a bike.  Where does the energy come from?  Food!  There are inefficiencies with producing food and then inefficiencies when our bodies turn that food into usable energy. So, if you really want biking to make less of an impact, be careful what you eat!  Figure below shows how Physics actually plays a big part in your biking experience.

 

http://www.explainthatstuff.com/bicycles.html



Gears

An important part of the functionality of a bicycle the gears.  Simply put, gears make your wheel seem smaller or larger than it actually is and thus affects the energy you need to put into it to move a certain distance.  You can view a host of information about how bicycle gears work here: http://science.howstuffworks.com/transport/engines-equipment/gear-ratio.htm.  Below is a simple diagram that shows a little about how gears change the distance output.





Notice that for every one rotation of the big gear there will be two rotations of the little gear.  This is why the front gears one your bicycle are bigger than those on the rear.  You also gain leverage to make the energy transition easier because the pedals provide you with more leverage.

 

 

 

Explore your transportation energy consumption:

 

Calculate your transportation energy use:  Updated Transportation Exploration Energy Consumption.xls and input your results under http://www.colorado.edu/MCEN/SustainableEnergy/transportation/transportation.html

 

 

References

 

• http://rw-3.com/2009/06/chinese-company-buys-gms-hummer/
• http://pvcdrom.pveducation.org/MANUFACT/LABCELLS.HTM
• http://www.japaneselifestyle.com.au/travel/images/japanese_bullet_train.jpg
• http://www.rtd.com
• U.S. Department of Transportation, Federal Highway Administration, Highway Statistics (Washington, DC: annual issues), table VM-1, available at www.fhwa.dot.gov/policy/ohpi/hss/index.htm of April 21, 2008.
• U.S. Department of Transportation, Federal Highway Administration, Office of Freight Management and Operations, Freight Analysis Framework, 2007 provisional estimates, 2008.
• Cengel, Yunus A., and Boles, Micheal A.  Thermodynamics:  An Engineering Approach - Sixth Edition.  Boston:  McGraw Hill - Higher Education, 2008.
• http://en.wikipedia.org/wiki/Atkinson_cycle
• http://en.wikipedia.org/wiki/Stirling_engine
• http://www.futurecars.com
• http://www.fueleconomy.gov 
• http://inventors.about.com/library/inventors/bl_history_of_transportation.htm