Volume 2 Issue 3 - Diesel Articles

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Pre-Turbo Diesel Water Injection
Driving with a Tailwind
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Pre-Turbo Diesel Water Injection

Snake Oil And Water Don’t Mix

diesel-water-injection-ifog-cross-section-featureTerms like Nitrous, Super-Charging, Wastegate and other hormone-inspired phrases, leave the topic of Water-misting a little... dry; uninspiring to say the least. Water is not a fuel. By itself, water does not burn, dissociate, or otherwise directly increase engine power or fuel economy. But perhaps water does increase engine efficiency and fuel economy when it is used to eliminate or reduce waste heat processes that convert otherwise useful engine power into non-useful heat. Trust me, this heat, wherever it is created, has pump fuel as its origin energy source. That heat is fuel wasted that might otherwise go to propulsion.

The turbo is a major source of this heat. Whatever we can do to reduce heat manufacture during turbo compression will result in better fuel economy and lower exhaust gas temperatures (EGT). No snake oil claims here, just simple thermodynamic facts of life.

In this article, we will look at the facts behind the merits of pre-turbo diesel water injection (PTWI) as a pre-emptive cooling mechanism: a means to tame that waste heat mechanism and direct that energy to the wheels.

The Power of Disappearing Water

Your body is an engine: an organic power plant. How quickly a large room goes up in temperature when a crowd of people pile in. Water is our coolant. If we could not sweat, our temperature would never be held down to 98.6ºF. Water is essential to heat control for all life and living things. So how about applying this power to an overworked diesel engine?

One day, I was towing on an eight percent grade, headed for a downpour. I was listening to my fan roar and watching my coolant temperature rise. The rain lasted maybe 30 seconds, but 15 seconds in, I noticed a funny thing. My fan had quit running and my temperatures were near normal. Sure enough, as I exited the shower, the fan and the temperature spikes all began again. There was no question that the rain had effectively cooled my engine – if only for its brief duration.

Something similar happens to my body when I cycle in the desert. With its eight percent humidity, outdoor desert activity at 112ºF is lip blistering. Heat stress can quickly turn into fatal heat stroke as quickly as four hours after the onset of heat stress symptoms. On non-monsoon days, I pedal through this near lack of humidity and 112ºF in a white absorbent cotton long sleeve shirt. I carry two liters of water on my back and I can go through most of it within two hours. At the first sign of nausea or weakness, I get wet, no delay. Air conditioning on the fly: and it is amazingly effective.

sonoran_desert_licensedI was deep into the Sonoran Desert on my mountain bike at 108ºF when a monsoon storm came in from the East. In the distance, a wall of dirt could be seen advancing toward South Mountain and the breeze was whipping up.

“This should be a treat,” I thought to myself.

I had seen it many times, but usually from the radar display. This time I was caught out. Soon, wind-driven dust filled my eyes. The wind eventually gave way to rain: it came down so hard it hurt. I circumnavigated the lower relatively dry washes – which were filling up fast – and narrowly escaped being stranded; getting across the main wash before it flooded. By the time I drove through the final mile of water crossings, the storm had nearly passed.
Prideful and tattered, I arrived home to see my neighbors looking skyward from safely inside their open garages.

“But it’s a dry heat!” I yelled sarcastically, with arms spread like a stage win at the Tour de France.

“Experimenting with the meds again?” they replied.

I stepped into the shelter of my house to ponder the cooling power of water that I had just witnessed firsthand. When I had started my ride, it had been 112ºF, intolerable except for the water I had ported with me: now it was 86ºF and I was shivering. A 26ºF drop in less than one hour. Why?


Driving with a Tailwind

Here is a thought. Our vehicle, in stock configuration, is, at best, 35% efficient. For every three gallons of fuel burned, only one gallon actually turns the wheels. The other two gallons, 65%, is wasted. Much of that goes out the exhaust as heat. However, some of it is heat energy wasted in non-propulsion heat processes such as the heat generated during the turbo’s compression process. Imagine if we could redirect even ten percent of those two gallons back to the wheels? That would mean that our 35% efficiency could go to 45%. In theory, that would represent a 30% increase in fuel economy (45/35=130%). In other words, anywhere we can find and eliminate a waste heat process, our effort should be rewarded nearly three-fold. Who doesn’t like driving with a tailwind?

The biggest waste heat process we find in any forced induction vehicle is in the turbo-charger compression process. More specifically, the more compression that you try to squeeze out of the turbo, the more parasitic and heat producing it becomes. When you are making 400 HP with the help of an inefficient turbo at high elevation it will manufacture 475,000 BTU per hour of heat from the compressor. That heat – the power experienced by the turbo shaft, albeit with very low torque and very high (140,000) RPM – is the wheel power equivalent of 200 HP! That power has to come from somewhere: it comes from the conversion of exhaust heat to mechanical turbine work. For a better explanation, see Thermal Feedback explanations in former issues of maxxTORQUE.

Putting Out The Fire

This is where diesel water injection gets exciting: extreme turbo shaft activity. Here is an excerpt from Aircraft Gas Turbine Powerplants Handbook:

The injection of water into the gas path causes heat transfer. When the fluid evaporates, heat in the air will be transferred into the fluid droplets, cooling the air and making the gas-flow more dense. Diesel water injection in a gas turbine engine is then a means of augmenting engine thrust. Augmentation can be thought of as occurring in two ways.

First, addition of water to air in the compressor increases compression and mass flow.

Second, water cools the combustion gases which allows additional fuel to be used without exceeding maximum temperature limits... Increases in these three engine parameters results in a thrust increase in the range of 10 to 15 per cent.

Pilots, whose lives have depended on it, have seen it first hand. World War II fighters used anti-detonation injection – the common term in the aircraft world for water injection – to improve performance, permitting escape to higher altitude. Water injection helped launch B-52G Bombers with 200,000-pound weapon loads into Vietnam.

The injection of water droplets into compressor inlet ducting is now commonly used as a means of boosting the output from industrial gas turbines. The chief mechanisms responsible for the increase in power are the reduction in compressor work per unit flow and the increase in mass flow rate, both of which are achieved by evaporative cooling upstream of and within the compressor… Consideration is also given to the efficiency of the compression process... (J. Eng. Gas Turbines Power – October 2004 – Volume 126, Issue 4, 748)

In the case of an eight-engine B-52, you get more thrust. With our trucks, more torque.


In this article...

  • Driving with a Tailwind
  • Nine Myths of Pre Turbo Diesel Water Injection
  • Water Properties that Aid Diesel Water Injection
  • Compressor Blade Impingement
  • Psychrometric Chart
  • Introducing Induction Fog (I-Fog)

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Comments (2)add comment

archimedes said:

archimedes
where could i get an i-fog system?
i would like to try the device.
 
August 23, 2010
Votes: +0

csamrice said:

csamrice
...
where could i get an i-fog system?
i would like to try the device.
 
December 14, 2010
Votes: +0

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