It could be my imagination but it seems like my 97 VR6 engine runs smoother & picks up speed better in damp conditions. It pulls well anyway but there does seem to be an improvement in the wet. Any ideas as to a potential technical reason for this or is it just a "fluke" ( or my imagination of course !).
Cheers,
Sparks
|
It is likeley to be true. Believe it or not a little moisture aids the combustion process. Plus moist air is cooler. cooler air is denser and combusts better.
|
|
Is that due to more oxigen in humid air from the water?
|
In general, engines perform better in cold-humid weather. Cold air is denser - so you get more air for the same volume - and humidity makes combustion "smoother", so more work is produced by the piston.
Vagelis.
|
This is only true at full throttle when manifold pressure is same as atmospheric pressure. When throttle is not fully open there will be a pressure drop across the throttle and manifold pressure (and hence inducted air density) will be below atmospheric.
This is all taken into account, of course, by the MAF/MAP sensor (the former inherently compensates for altitude and temperature variations; the latter usually have an additional air temp. sensor incorporated into the EMS).
Moisture in the air is thought to help combustion because the molecules of water 'explode' during combustion, improving the fuel atomisation and leading to a more thorough and uniform burn. This is especially notable in diesel fuels - a few % water added to diesel greatly improves fuel atomisation and hence the thoroughness of combustion - it is being investigated as a way of reducing particulate emissions (i.e. soots - or partially unburned fuel).
|
|
with ref to aprilas point about the benifit of low temp/ higher humidity only being relevant at full throttle openings, surely(?) the power increase will be at all throttle positions, the fact is the temp/density of the air on the manifold side is still directly related to ambient figures regardless of the throttle valve position , that the air is of course at a lesser pressure on the manifold side and therefore less dense at all but full throttle positions should not effect the overall increase to be found in these conditions, of course the maximum benifit will be at full throttle position when manifold pressure is roughly equal to atmospheric pressure,.... or i missing something here? if i am im sure someone with far greater knowledge than i will put me right!
|
|
You are correct that *for a given throttle angle* marginally more power will be available at a low air temp than at a higher air temp. However, normally the driver will compensate by having the throttle marginally less open to achieve the desired speed/acceleration.
|
|
|
|
I guess this explains why several tuners install water jets in the air-line of highly-tuned turbo engines.
Which, BTW, makes me wonder: you have to observe the water level of yet another tank in the car, right?!
Vagelis.
|
|
|
|
|
Yes, well-known old wive's tale that turns out to be true, not just imagination.
Does the car have a device for diverting in hot air until it is fully warm? Might be worth checking that the thermostat is fully cutting it out once warmed up. If warm air is leaking in, the conditions you note would exagerate the improvement in running.
|
A qick Google at 'water injection petrol' brings up a wealth of information. Good interesting info on not only the history, but practical examples of competition use in Formula 1 and rally use by Saab.
website.lineone.net/~da.cushman/misc/mannject.html for further reading.
pmh (was peter)
|
Water injection is primarily used on turbocharged engines, both petrol and diesel, sometimes to spectacular effect!
Ever seen a Diesel powered tractor puller? You'd know what I mean then!
|
Getting back to Sparks' question, folks - do you really think one could tell the difference between dry and wet weather engine response in a 97 car?
I am not doubting Sparks' abilities, it is just that, whilst I know and understand the theory, I would have thought that in day-to-day driving the difference is too small to detect, even in a new car
Is it possible that there is a small problem with the car in the dry which is not present in the wet? Just an idea...
|
Golf VR6 is a fairly modern day engine - I wouldn't be suprised if the difference (in a fault-free engine) could be detected.
My VR6 I had a few years back definately felt more spritely in cold weather, usually on a Sunday morning!
|
|
Do you think this phenomenon is more noticable in the VR6 as opposed to other engines/ designs? I like to think I have a pretty good feel for these sort of things but never felt this before. Never driven a VR6 before either but it is on my (long) list.
|
Possibly, yes, with the tight and cramped (hot) engine bay.
You must drive one and soon! It's a real gem of an engine. I covered 40K in my MK2 Gold fitted with a VR6 engine - a real blast of a car!
|
many thanks for the input ( and hugely impressive technical info! ) everyone. I guess there could be a "dry weather fault" with my VR6 but it seems to perform well all round really - it just feels a wee bit more eager in damp conditions.
For the record, I think the Golf VR6 is a fine car and great fun to drive, notwithstanding that the handling could be a lot better ( depends how fast you want to navigate bends though really! ) and clearly other more modern machinery has overtaken it dynamically.
Cheers,
Sparks
|
|
|
