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Friday, June 27, 2014

Trade some fuel for water...

     With the cost of fuel rising again, I have been fielding alot of questions recently about turbo- diesels, combustion, and improvements for them.  One of the oldest ways to improve TD performance is still one of the best, easiest and most reliable methods to add power and efficiency without extra heat or significant cost.  This old but useful system has been improved by modern technology, materials and control alogrithms.  This simple add on that adds so much for so little relies on some basic properties of one of our most abundant resources on this planet: water.  (distilled- not out of a faucet).

Heat is a killer, no doubt about it.  Without an active, properly functioning  cooling system, an engine would overheat and self destruct in in a matter of minutes at full load. 

Adding too much heat anywhere in an engine can be disastrous, or at least inconvenient when the high temperatures force your foot out of the throttle to keep temps down and the loss of power and speed that follows to prevent engine destruction.  The direct opposite is true as well:  The more heat you can use from combustion to do actual work the better and more efficient the whole process becomes.   

A turbo-Charger helps the efficiency of an engine by moving and compressing the air at a higher efficiency rate than the engine can by itself.  In assisting the engine by compressing more air into each cylinder however, the compression process in the turbo-charger inherently adds heat to the intake air in direct proportion to the compression ratio of in vs out pressures.  Adding pressurized air to the intake of an engine, good...  Cramming HOT pressurized air to the intake, BAD- adding more heat from combustion puts the temperatures way out of design parameters

 Additional heat added to the air going into the engine can raise combustion temperatures to unsafe levels and start melting valves, valve seats, piston crowns, etc.  Intercoolers- a name referring to air-to-air heat exchanging radiator out front in a machine- are commonly used by OEM manufacturers to lower compressed intake air temperature before it enters the engine. 

Rudolph Diesel- (Wiki Link ) - inventor of the diesel engine, knew of this requirement of cooling the intake air if it is to be pre-compressed, and in some of his patents, he included a water/methanol injection system to spray a fine mist of water/ alcohol into the compressed air to remove excess heat. 

There are 5 different ways that water injection helps increase the efficiency of the engine. In order, through the intake and out the exhaust, these benefits are:

     1) Cooling the intake air charge means more oxygen can can get into the combustion chamber because cooler air is denser and thus more air, more oxygen, add more fuel, get more power.  A small amount of water can absorb a large amount of heat from the post turbo compressed air.  Adding methanol to the water tank improves this effect.
      2)  It is a small effect, but not negligible, that the water is non- compressible and will raise the effective combustion ratio of the engine and thus burn more fuel more completely to produce more power.

      3) In combustion, some of the water (H2O) in the presence of high combustion temps cracks into a naked hydrogen ion, and an OH radical that 'walks' down, or 'unzips' a fuel molecule rapidly and more completely, and results in more of the fuel being burned.  Most of the water that gets cracked like this recombines into water after this separation, but some is lost in chemical reaction. Methanol at this stage of the process acts partly as fuel, partly as a OH contributor.

      4) Some of the water in the cylinder gets turned into steam, absorbs some heat (IR) and lowers overall combustion temps while adding the energy of roughly 1600:1 expansion from water to steam to the power output of the engine. 

      5) All the way out of the engine to the turbo, the remaining water in the exhaust flow also extracts more heat from the metal and adds yet more density to the exhaust flow out of the turbo.   More pressure and higher density exhaust combine to help spool the turbo more quickly, thus drive it to full intake pressure sooner.

 The whole system feeds back on itself and improves the fuel economy and power output of the engine the system is installed on.   Adding water and enough methanol to prevent freezing for projected overnight lows to the combustion process adds several benefits.  

Adding more oxygen due to greater density allows us to burn more fuel for alot more power without destrying the engine OR, we just lower the temps, get a small power boost and improve fuel economy substantially.  How the system is configured determines when and how much water is injected based on exhaust gas temperature (EGT) and boost pressure or in more sophisticated systems, many more inputs.  

Water is relatively cheap and abundant and comes out largely the same as it went in.  Along the way it can help make more power, increase fuel economy, lower combustion temps and thus increase usable engine life.  The payback from fuel economy for me happened after about 1-1/2 years of normal driving, with more driving the return could be quicker

Great ideas never pass away, they can be passed over for a while tho.  This is another idea that has been passed over for too long.  More please.  And soon...

Until then...  MW out.

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