Volume 2 Issue 3 - Diesel Articles

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