London Lad wrote:

OK, just discussing here, not arguing

Based on your explanation you can never get improved fuel efficiency ?

Lets say a D3 does 27mpg average. It then gets re mapped, the driver drives the same but experiences improved economy say 29mpg average.

Where did that come from ?

London Lad wrote:

OK, just discussing here, not arguing

Based on your explanation you can never get improved fuel efficiency ?

Lets say a D3 does 27mpg average. It then gets re mapped, the driver drives the same but experiences improved economy say 29mpg average.

Where did that come from ?

No problem discussing

Of course you can get efficiency gains (up to a point), usually limited by how unecessarily inefficient your starting point is. The point about hydrogen is that the hydrogen is being proposed as a fuel, "freely" obtained from water and will lead to an offset/reduction in diesel consumption. As expained this is impossible as the energy the D3 engine expends via the altenator is more than the energy content of the hydrogen produced so it cannot offset usage of diesel as the engine will consume more diesel to produce the hydrogen. And that assumes the diesel engine can usefull extract/use the energy in the hydrogen. So hydrogen cannot usefully act as a fuel in this scenario. That debate isn't really even about efficiency as such, its main claimed benefit is to substitute a free fuel for a costly fuel.

As we have both agreed, you can get efficiency gains from water injection - this is actually just the same efficiency gain as an intercooler gives, it just is more efficient as the water is very effective at reducing the charge temp, especially in turbo engines which generate more charge temp by the compression effect of the turbo. The limit of water injection is normally the amount of water you can carry, if used constantly it would require a fair amount, hence usually limited to full-throttle performance increases as with your Saab. The water injection uses a miniscule amount of electricity as a) it is only a pump and b) it only runs for short bursts at full throttle, hence there is a negligible amount of extra fuel burnt to get the effect hence a net, sizeable gain in output from the same engine size (different kind of efficiency, the hp/litre rises rather than mpg).

As the hydrogen system starts with water it would be better to just pump the water in rather than split the molecules and feed them in seperately....

Remaps. As the basic engine stays the same and only boost and fuelling (simplistically, there are a few other things that can have their operation altered) is altered a remap only gives performance that the manufacturer could have given if they chose to. Typically it is possible to get huge outputs from turbo charged engines in exchange for (very) short engine life. As an example David Vizard obtained >400hp/litre from a turbo 2L pinto in the 80's.....for about 20secs. Manufacturers have other considerations than outright engine efficiency, such as driveline longevity, warranty performance etc etc. Basically if they up the performance they will increase their warranty costs to some degree. In addition to their assessment of driveability and many other criteria they choose a level of tune appropriate to their needs. One of these criteria is that the LR tune must work all around the world, I haven't seen anyone suggest for instance that a UK remap on a TDV6 will be fine and dandy in the desert, under sustained usage in hot conditions the intercooler performance will be reduced as it works on there being a good differential temp between ambient and the charge passing through it. If you crank up the boost and fuelling via a remap AND subject it to the harshest conditions LR envisage then it may give problems as the charge temp rises. Mine won't go near the Saudi desert AND be towing a trailer at the same time in low range so I'm not worried but LR will be.

Having raised the boost and fuelling the engine will produce more torque and hence will be more efficient at lower engine speeds, the gearbox (or driver) adapts as the torqier engine has an easier time moving the car hence you get an efficiency gain.

Even LR retuned their D2 autos to give more torque as the poor driveablity was hitting sales and with no sales you don't have a warranty claim issue

Did any of that help??

wantsanlr3 wrote:

It comes from the remap using the fuel more effeciently. Although this could mean more stress on parts. Car manufactures have to juggle engine efficientency with longevity.

Oh crap, could I just have said that instead

simonsi wrote:

wantsanlr3 wrote:

It comes from the remap using the fuel more effeciently. Although this could mean more stress on parts. Car manufactures have to juggle engine efficientency with longevity.

Oh crap, could I just have said that instead

phurley wrote:

I don't think London Lad was actually asking how remaps work. I think he was challenging, rightly, your notions that the conservation of energy applies here.

phurley wrote:

Also, I think you may have overlooked that the chemical energy of fuel is not directly related to the mechanical work it can perform in an IC engine.

The chemical energy is usually far in excess of the work that can be usefully extracted by the ic engine, petrol is less than 40% efficient, diesel slightly better, I don't have figures for hydrogen but don't expect it to be much different. This makes the energy cost/benefit of hydrogen as a fuel when the electricity to generate the hydrogen is self-generated even worse. Hydrogen cars such as BMWs prototype assume cheap electricty from a grid source is used to obtain the hydrogen. Even then the hydrogen has a habit of escaping from the tank over time....

phurley wrote:

In LR's case, for example, the more fuel-efficient TDV6 is not even available in the US - and they already make the car!

London Lad wrote:

I am still not sure that your calculation of the 'cost' of the electrical energy is correct in this scenario, but as it looks like most people here are far better qualified than I am I think I'll wait, watch, listen and learn.

Not my calc, that was from the guy who works with this stuff day-to-day I agree with him though...

simonsi wrote:

London Lad wrote:

I am still not sure that your calculation of the 'cost' of the electrical energy is correct in this scenario, but as it looks like most people here are far better qualified than I am I think I'll wait, watch, listen and learn.

Not my calc, that was from the guy who works with this stuff day-to-day I agree with him though...

phurley wrote:

I don't think London Lad was actually asking how remaps work. I think he was challenging, rightly, your notions that the conservation of energy applies here. He's simply pointed out one example of how to increase efficiency from an engine without violating any thermodynamic principles.

Other examples include EGR (inert gas), oxygenate fuel additives (less chemical energy), combustion chamber design (higher compression ratio & shaped flame-front), exhaust flow design, etc.

Also, I think you may have overlooked that the chemical energy of fuel is not directly related to the mechanical work it can perform in an IC engine. More relevant factors are specific energy (potential energy relative to its stoichiometric air:fuel ratio), combustion products volume, flammability limits, flame speed and flame temperature.

What is relevant is whether any specific hydrogen generation system actually works in a vehicle. Granted, I have yet to see any respectable, independent validation that answers skeptical questions like,

How does it affect the combustion chemistry?
What volumes are necessary to produce the desired results?
Does it force engine design changes?

However, that absence isn't definitive of the possibilities. The reality is that manufacturers have limited interest in producing more efficient vehicles (for a given purpose). There are a multitude of considerations, mostly centered around cost, that create so much inertia that progress is slow. In LR's case, for example, the more fuel-efficient TDV6 is not even available in the US - and they already make the car!

At least, it seems there are some volunteers...

Well theres all kinds of wrongs in this but I'm just going to pick out one and I think you will find that the first law of thermo applies to everything in life and for that matter death too

chemical energy of fuel is totally directly related to the mechanical work it can perform in an IC engine. You cant get any more energy out of it then its capable of producing and If you can figure out a way to do that You would probably create peace on earth...

ok maybe two...

As far as the TDV6 goes americans in general have a bad taste for diesel they picture black smoke comming out of old rattly mercs, and also I dont believe the TDV6 meets US epa standards and then theres also issue of our low sulfur diesel.