The Red Brick Times

An Adiabatic system is one in which no heat is gained or lost during the process. In a Diesel Engine the compression cycle is done adiabatically, with the air squeezing taking place in such a short time that the air heats up beyond the point where the diesel fuel bursts into flame. The heat is built up much faster than it can flow away through the cooling or oil lubrication system. That is one reason that diesel engines work best when they are hot, the combustion occurs more readily. Adding ceramic materials or coatings (like the tiles on the space shuttle) have two potential benefits: 1) they keep heat where it performs work (pushing pistons and not wasted by heating up the metal of the engine) and they may be engineered to be extremely hard and abrasion resistant. Cylinder walls have been impregnated with nickel - silicon ceramics for many years, both to increase heat resistance and to reduce wear. Ideally, an adiabatic engine uses all of the heat energy to cause mechanical motion, and none is sent out the exhaust pipe or through the water cooling system or through the oil cooling system. The ceramic materials can be both impervious to heat, and moleculary smooth and carbide-hard to resist wear without the need for an oil film lubricant. Ceramics are also more brittle and less mallieable than are metals, so are less suited to the hammering that takes place in a reciprocating piston engine. Jet turbines, with their inherent rotating smoothness, have used ceramics in combustion chambers and on turbine blades for a long time.

Home heating furnaces have benefitted from higher efficiency by extracting most of the heat energy from methane (natural gas) to put into the house. The most efficient furnaces have exhaust gases cool enough to use PVC pipe for a chimney stack. The heat is extracted before the gas is exhausted outdoors. Heat exchangers have been coated with ceramics for resistance to corrosion and acids formed in the gas cooling process.

Automotive catalytic converters are tightly cast honeycombs of ceramic material coated with molecule-thick washes of platinum or palladium. The ceramic substrate provides huge surface areas, while the metallic coating allows unburned hydrocarbons to oxidize at lower energy levels (temperatures) than normal. Too high a catalyst temperature creates NOx (oxides of Nitrogen) which contribute to pollution as much as do Volatile Organic Compounds (VOCs) or unburned hydrocarbons (HC) at too low a temperature. So the Heated Oxygen Sensors (HO2S) in the exhaust feed back to the engine brain to keep control of the mixture so it stays in the most effective range for the catalyst action.

If we could create hot expanding gas without making poisonous by-products, then we could do away with catalytic converters on the exhaust. Hydrogen makes water when it burns. But if there is too much hydrogen for the oxygen present, then other acidic or noxious compounds could be formed in the exhaust. If there are sulfur compounds in the air/fuel system, or if there is nitrogen in the air/fuel system, we are back at dirtier exhaust, even if we are burning hydrogen.
Posted 11:28 AM by Andy (2) comments

       Comments:

Oh, so that's how it works. Nice post.

"Jet turbines, with their inherent rotating smoothness, have used ceramics in combustion chambers and on turbine blades for a long time."

Please adapt one of those for use in my next car. Something sporty. Red would be nice.

# posted by  whatley : May 02, 2005 6:44 AM
 
I've been on BI all week and haven't been able to check in. To echo Russell, Nice post.Very concise and actually informative. I give it about 78. Any leads on where to research or follow current trends in ceramics?

# posted by  A. O. : May 07, 2005 8:37 AM
 
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