Re: why does exhaust energy from vehicles have to be realeased?

Greetings:

There are many types of engines for doing work and they all have one thing 
in common, they convert high temperature liquid, solid or gas materials into 
low temperature liquid, solid or gas materials and they extract power to do 
useful work in the process. These processes are based in the laws of 
THERMODYNAMICS. Generally, the greater the difference between the high and 
low temperatures inside the engine, the greater will be the useful power 
output and efficiency of the engine. If a process were invented to collect 
the exhaust products from an engine, you would still have to raise the 
collected exhaust products to high temperatures to obtain useful work out of 
them. The best engines would have exhaust products that do not pollute the 
environment and that could be recycled through the engine. In the following 
discussion I’ll present some possibilities for clean, recyclable exhaust 
products. 

Engines that run on gasoline, methanol and diesel fuels are called internal 
combustion engines (ICE) and they use the rapid explosion, heating and 
expansion of a compressed fuel air mixture in an enclosed cylinder to drive 
a piston downward during the power stroke. Currently internal combustion 
engines have a number of advantages over external combustion engines with 
the explosive fuel being part of the heating process being a major 
advantage. 

Steam engines are external combustion engines (ECE) and they use an 
external fuel combustion process to convert liquid water to high-pressure, 
high-temperature steam in a boiler. The high-pressure, high temperature 
steam is then transferred into the cylinder to drive the piston during the 
power stroke. However, a steam-generating boiler and heater also have to be 
added to the vehicle to run an ECE engine. Because steam engines run at 
lower pressure and temperature differences than ICEs, they must use larger 
diameter pistons (greater volumes of gas) to produce the same amount of 
drive power and thus they are less efficient. Closed cycle steam engines 
have been operated that reuse the low temperature exhaust steam and water. 
However, this does not increase the efficiency very much; however, it does 
reuse the water. 

Fixed rate of combustion processes can be used for steam boilers and 
also for hybrid electric vehicles and they  can be designed to generate far 
less pollution that current ICEs. Here in California, to reduce air 
pollution, a number of manufacturing plants now use pure oxygen instead of 
air with petroleum based fuels for their ICEs and heating systems. This 
combustion process eliminates the harmful nitrogen compounds released when 
using air as an oxidizer. However, the oxygen must be stored at very low 
temperatures in large cryogenic tanks. These large fuel tanks are not 
suitable for use in vehicles.

The hydrogen/oxygen fueled engine and or boiler would be one of the 
cleanest engines with water and steam being the exhaust residue from the 
process. One of the problems with these engines is to safely store hydrogen 
fuel and oxygen oxidizer. In California we have a number of hydrogen fueled 
busses operating which use the oxygen in air as an oxidizer. They are very 
clean but do produce some nitrogen compounds. The busses use large hydrogen 
fuel tanks filled with hydrogen absorbing materials such as nickel hydride 
to reduce the pressure in the fuel tanks. 

Hydrogen/oxygen fuel cells that can generate electricity in a clean process 
is another concept being studied for electric vehicles. Currently, cost 
effectively generating, storing and delivering hydrogen gas is an important 
part of the fuel cell concept being studied. If you  search the Mad Science 
archives for fuel cells and hydrogen, it will return a large number of 
questions and answers that address the problems and potential of using 
these environmentally clean processes for motor vehicles, spacecraft and 
for aircraft.

Currently, research on fuel cells, new batteries and hybrid vehicles are 
the concepts most favored by the world’s automotive industry for future 
clean, efficient vehicles. The infrastructure to deliver the fuel to the 
consumer must be considered for it is also an important part of the overall 
process.

Best regards, Your Mad Scientist
Adrian Popa