Diesel air intake warm or not
 

I have read that diesel motors run most efficiently on cold air and I have read that they run most efficiently on warm air.
Most who drive a diesel notice mpg losses threw winter. Could the cold ambient outside air be responsible ? or has it nothing to do with cold air and more to do with winter mixed diesel. Is the winter mix diesel in all gas stations and what months would it be used.
Do people realize poor cold weather mileage even on summer diesel ? If so would warm intake air aid? or is it more to do with a cold block than poor combustion.

A turbo compresses the air in that process the air gets heated just by being compressed it also gets heated by friction and the hot exhaust gases on the turbo. The intercooler, cools that hot air.
When driving efficiently I am not using my turbo or intercooler, the air is not being heated up by the compression of the air in the turbo, meaning it is not as hot as it normally is.
"This would be the time that warm air intake could aid the burn"(my opinion)

Here is some food for thought, if running warmer intake air causes higher combustion chamber temperatures could it mean a more complete (hotter) burn occurred?.:eek:

Within reason, cooler intake temperatures will increase a diesel's efficiency (assuming you don't get so cold that the ignition delay gets very long and approaches misfire). Just look at the efficiecny of an intercooled vs non-intercooled turbodiesel. The cooler air will make the engine run leaner which generally increases the thermodynamic efficiency, as does the colder air temps themselves (via the specific heat ratio).

That being said, cold ambient temps hurt a diesel in pretty much all the same ways it hurts a gasoline car. I personally have observed about a 1% decrease in FE for every 1 deg C decrease in ambient temperature. About half of this can be attributed to the increase in aero drag via the increased air density. The rest is due to the increased rolling resistance of the tires, and the increased warm up times.

I've heard folks blame the winter fuel, but I don't put too much stock in that myself. Summer diesel is #2 diesel fuel, whereas winterized diesel is a blend of #1 & #2 diesel. Pure #1 diesel contains, on average, about 4% less energy per gallon than pure #2 diesel. That's not completely insignificant, but it's pretty small (especially considering that, in most areas the winterized diesel doesn't go all the eay to pure #1).

I've kept track of all my daily mileage all winter long and I've cleary been able to see the ambient temp effects, but wasn't able to make out any clear tank-to-tank variations.

Thanks for that information Diesel Dave.
It would be nice to get to the bottom of this, fuel "may" be getting wasted by as much as 10% in the winter months if people are feeding their diesels cold air on a cold winter day.
Would the oxygen sensor in the exhaust control any over fueling
caused by the warmer and lets face it more combustible air
Could less dense (warmer air) actually use less fuel to burn then the cold dense winter air
I would like to find a study on air temperature and diesel economy not air temperature and max diesel hp.

I found a website that deals in commercial diesel engines and its performance intake air temperature is reported to be 25*c which would suggest to me that warm air(not hot air) is better for combustion. It has been a challenge to find info on diesel intake temperatures.

Diesel engines for fast vessels with low load factors

Maximum performance rating

e.g. fast yachts, corvettes and frigates

Power ratings classifiable

Intake air temperature 25°C

Sea water temperature 25°C

Power reduction at 45°C/32°C

- Series 8000: none
- Series 1163: 3.0%




Diesel engines for fast vessels with high load factors

Maximum continuous rating

e.g. fast ferries, yachts, corvettes and frigates

Power ratings classifiable

Intake air temperature 25°C

Sea water temperature 25°C

Power reduction at 45°C/32°C

- Series 1163: 4.6%
- Series 8000: none


Combined propulsion plants with diesel engines and gas turbines: MTU Online

Almost every thing that has a temperature dependent rating uses 25C as a base line temperature because its room temperature. A common reference point makes it easier integrate different components and systems.

Edit: It is part of SAE J1995 test standards for engine tests to be done at 25C

Diesel engines are more prone to the effects of cold winter temperatures because of they are more efficient than gassers. Greater efficiency -> less waste heat -> longer warm up time. Once the engine is up to temp it is still losing lots of heat to the freezing air flowing through the engine bay. Now, diesels like to run hot for efficiency, but keeping it hot in the freezing wind may be impossible.

My turbodiesel likes to stay around 78°C without the upper grille block. With the upper grille blocked, at temperatures slightly above freezing, the warm up process will plateu at 78°C, then go to 86-90°C after a longer acceleration or hill climb, and stay there. At the higher coolant temp the idle consumption is slightly lower (0.48-0.52 liters per hour vs. 0.50-0.54 lph). This last winter I had a cold start at below -18°C, no prewarming, and it took me twenty-something kilometers to get to 60-65°C. During the ~400km drive home the coolant temperature hardly ever got above 76-77°C, a 3km EOC would instantly cool it by at least 10°C. I told my passengers to keep their coats zipped and hats on, because trying to heat the cabin would bring the coolant temperature down to 70-74°C. In other words, even though I had both my grilles blocked and heating to the bare minimum (just enough to keep the windshield from icing over), the engine never got to its optimal operating temperature. Other than very low temps, driving conditions were ideal: sunny, dry, no wind, low traffic. Milage sucked on that trip.

Maybe the cold air going into my intake lowered my milage? On many occasions I've noticed that, even though it was cold (-10°C), by the time the intake air made its way around my engine bay (my filter box is behind the engine, so I have lots of prewarming before the air enters the turbo), its temperature was between 15-25°C before the turbo, where the temp sensor is. I have no idea what the temperature was post-turbo and post-intercooler, but I seriously doubt it was lower than 25-35°C.

On the other hand, in the summer my pre-turbo temps can get up to 50°C, and the idle consumption doesn't get lower, even though the engine is hot (90-98°C).

On a tangentially related note, In 1963 Rover entered a turbine powered car in the 24 Hours of Le Mans race, and averaged 6 mpg. A year later they averaged 13 mpg with essentially the same engine, only using the exhaust air to preheat the intake air. With hot intake air the engine was down several horsepower, but since it was able to go twice as many laps between refills, its overall performance didn't suffer much.

I have often wondered if preheating/reheating the fuel and intake air might result in FE gains with diesel engines.

Rover's 1964 turbine car entry at Le Mans...

http://www.rover.org.nz/images/roverBRM.jpg

Thanks for posting up guys, we will get to the bottom of this,peoples first hand experiences are going to point us in the right direction.
optimal intake temperatures do exist..
I think I found some good info about commercial diesel motors and intake air temperatures.
This report on turbo diesel motors cannot stress enough how important it is to have intake air temperatures as close to the coolant temperature as possible. It may well be that in our diesel motors that great variation in coolant and intake air temperatures is hurting efficiency.

have a look at this informative and interesting
( if your a tech junkie) read on intake temperature of a turbo diesel.
http://www.mandieselturbo.de/files/n.../5510-0005.pdf

And Stan WOW that is encouraging and actually sounds like proof of the benefit.

Stan actually when regeneration is used with a turbine it is used after the compressor and not at the intake. The following should clear up how it works for you.
http://web.me.unr.edu/me372/Spring20...generation.pdf

Unfortunately regeneration is hard to do in a piston engine.

from the article
"The density of the air will be high when
the ship is operating in arctic conditions
with a low turbocharger air intake
temperature. As a result, the scavenge
air pressure, the compression pressure
and the maximum firing pressure will be
high.
In order to prevent excessive pressures
under such ambient air temperature
conditions, the turbocharger air inlet
temperature should be kept somewhat
higher than the ambient air temperature
(by preheating, if possible)."

Nothing to do with efficiency just engine longevity.

Also as noted in the article some ships use exhaust gasses for steam production and a drop in EGT caused by cold air intake could reduce steam production below the minimum required level. This really is applicable to a car.

On further reading in that last pdf i noted that with every 10 degree Celsius increase in turbo inlet air causes a reduction in fuel economy by 0.7%

I think that paper did not help my theory !
it did say that -10 to 45 c was their diesel motors optimal running temperatures. It could be they will perform poorly and use more fuel outside of those best working conditions.

Good stuff. I enjoyed the article...thanks! I don't know that it really "proves" anything, but I DO think it hints this line of research is worth looking into. Small, high-speed diesels aren't MAN ship engines (80cm bores...300 RPM :eek:), and they certainly aren't gas turbines, but there may be benefits to FE from running under near isothermic conditions.

An easy-to-do first-order swag might be to rig a "hot air intake" by drawing intake air past the exhaust pipe and by routing the fuel line past a hot water line. Anybody ever tried this?

Nope and I don't plan on it.
Unless I move to AK or ND.

After some more thought, it dawned on me that the 10 degree increase at the the turbo that would increase fuel usage by 0.7% was just that at the turbo.
I am more concerned with fuel usage when not using the turbo.
Means that the turbo's extra hot air after it has been compressed and heated by the turbo will not like to be increased without loss of economy. When cruising and not using the turbo the inlet temperature is cool to cold on most driving conditions and may very well benefit from a warmer intake temp. In the dead of summer, the road baking hot, air being sucked into the intake is hot, being sucked from 6 inches off the hot pavement(my car) it is hotter then one would suspect,my car gets its best mpg during the summer.
Here's a idea Stan, run a hair dryer on high heat and med heat into
your cars intake, say after the air filter, and note any changes to your {if you have one, i don't) fuel economy device with the car at idle.
Piwoslaw or Diesel Dave or anyone else if you have a fuel economy gauge and a hair dryer or as Stan suggested, run a heat safe hose from over your exhaust to your intake and note any differences
for the good or bad by preheating the air.
If I had a gauge I would be doing the test myself.

Good idea. I have a VAG-Com. Anybody know off hand if that will work?

Here is a link to the Vag Com website.
Ross-Tech: VAG-COM: Fuel Trim Info
where it talks about fuel trim, I am thinking maybe looking at these numbers before heating the air and after heating the air. There could easily be a better method for Vag Com to be used for reading any changes. I am not familiar with
vag com.
Anybody have the knowledge?

My winter MPG losses at last winter were because of winter diesel, because engine could not reach optimum temperature in cold, I needed cabin heater which took so much heat that even with grill blocks it was too cold wind under the hood for engine to stay warm, also because most of driving was in deep snow, sometimes more than 4 inches and they are now going to reduce road upkeep further...

It might be even worse with warmer air, cold air probably helped a bit as cold air has more oxygen.

Boost gauge did sit at 0.2-0.3bar when driving on snow, while normally it is at 0bar mark, maximum is around 1bar.

With petrol car that had been given bit more aggressive cam etc. it was interesting to note that during the summer at cold places (temperature sensor at intake pipe and laptop logging / instruments), car did go easier, throttle position must be lowered to not increase speed, injector open time was then shorter.

Of course there must be the limit for that, if we think about ethanol, it has trouble making good mixture with cold air, which partly leads poor starting below zero, maybe there are such points for diesel too, glow plugs are there because of reason, if colder would always be better surely glow plugs would not be needed.

Compression makes diesel and air hot, so that it does ignite, if air is so cold that compression does not reach enough heat, then igniting will be poor, so surely there is optimal temperature and too cold will not be good.

Some effects are of course because of cold fuel, which makes it bit harder to find out which is what.

I vote for 10C or around there, purely a guess, but I would consider that being good one.

Then think about humidity in air and how water increases efficiency, in cold air there is less water, what that might affect? I know that after the rain when weather is damp car likes to fly ;)

Sounds like you want to know what happens with a normally aspirated diesel then. The results of temperature and atmospheric pressures are discussed in this NACA paper from 1937 (Note the discuss both fuel economy and power at variable loads). http://aerade.cranfield.ac.uk/ara/1937/naca-tn-619.pdf

That has a lot of information in it ConClark. I am finding it hard to get any usable data from. It mixes altitude and air pressure in the data that in my opinion renders the results unfit for comparisons purposes with a road car. If you feel I missed something from the paper that you feel is important please post up with it. I am not not trying to learn from the paper it just seems to be data of another direction, aircraft to be exact.

Figure 14 has data in it to where atmospheric pressure is held at sea level and air inlet temperature is varied along with the quantity of fuel injected. If you look at the bottom of that figure you will find that they give chart fuel consumption in lbs of fuel per hp per hour.

The trends in the data for the sea level test results is directly applicable to an auto diesel with similar intake temperatures and fueling.

That chart reported -3 as ideal if i am reading the chart right.
I do not buy it, seems counter intuitive to real life data of hard starting and poor mileage diesel owners experience during winter.

The premise is that the car will make less hp and use less gas.

My deduction could easily be flawed but here it is in a nut shell. Cold air has more explosive potential and hp than warm air when in a compressed cylinder because the air is denser.
The sensors on the car keep the air fuel mixture correct, the colder denser air would need more fuel to stay at the correct level. With warm air the car would lean out the mixture to correct the air fuel mix. As a bonus the warmer air fuel mix ignites a substantial amount easier.

Diesels seem to want as much mass as possible stuffed in their cylinders to get the best fuel economy.
EGR delete, free flowing intake, ram air, water injection and turbo chargers all show FE gains on diesels.
One of the most important factors with FE is getting your diesel engine up to operating temperature.

If you think about it, that all leads to conclusion that as piston compress stuff certain amount, if there is more stuff you gain higher CR and higher CR always improves things until it becomes too high.

That is at least image what I'm getting.

Real life results have always a lot of variables, cold starting, engine not staying at optimal temp, if short driving, drivetrain has more loss because oils and greases becoming thick and most of effect comes from cold, maybe using winter tires, winter diesel etc.

Also while air has more oxygen, it has less water, that might have something to do with something too, at least skin and throat becomes dry more easily ;)

Here is where you have a problem. Diesels operate with excess air, hence the reason they have no throttle.

I think it's a bit more complicated than this, this is what I am seeing.

A diesel doesn't need to maintain any kind of air fuel mixture, it just injects however much fuel it needs and spits out however much power. Press less on the pedal, less fuel is injected.

The issue is that since colder air has a greater amount of oxygen available, the fraction of fuel injected for the same power level is lower. I'll be taking a sort of metatheoretical view just thinking about temperatures. Less fuel fraction means when the fuel burns, you have a smaller change in temperature and pressure, which is not good. However, a lower temperature to start with increases the maximum possible theoretical efficiency, so it's really not clear what will happen.

Coming back to reality, we see there's another thing about cold air that makes it more complicated. The heat ratio of gases is not truly a constant, and tends to decrease with temperature. In an ideal cycle with ideal gases higher heat ratio is better, but I imagine in the real world the advantage is dulled a little.

This is all not considering combustion quality, which of course can be affected. If you're having trouble starting a diesel engine, that probably means combustion stability is an issue and you'll be seeing a greater effect from that than the ~10-20% absolute temperature changes that happen between seasons.

I could try one day when the engine will be hot, though now it's getting warm outside, so I'd be comparing a W(arm)AI with a H(ot)AI, I'd have to wait 6 months to test a C(old)AI.

But I wonder if this test would show anything conclusive. Since I don't have a dyno, then I'd just be idling on the driveway. At idle I see ~23% load and ~760rpm, while 80% and 1800-2200rpm would be ideal from a hypermiler's point of view.

Also, my turbo has variable geometry, so it may be that the amount of air getting scooped up depends on more than just the amount of exhaust gases coming out. For example, the ECU will see that the intake air is warm, so it will change the turbo's geometry to force more air into the cylinder. Then the only difference between tests would be the temperature of the air in the cylinder, not the amount, i.e. the amount of air (mass-wise) is constant, but if it is warmer, then it gets crammed in at a slightly higher pressure.

I run water injection.
When I have air in the system and the water pressure is randomly cycling up and down I can feel the difference as the water cuts on and off.
I can tell my diesel likes the water injection, it did not like propane injection.

Thanks everyone for their input, I am still curious to test the ole hair dryer in the intake out. I am going to get Vag Com installed on my laptop , I had the free version before but lost it due to a reformatting the hd.

It may be best to have a light foot on the old gas pedal thereby using less fuel, ha ha bet we all new that already!!

What everyone has been saying makes sense and helps refresh my mechanical knowledge, or lack of.
This is my first diesel

My idi 2.0L Mazda RF diesel engine has an air heater plate between the intake and the air filter. Get's pretty warm to the touch.
VT247

http://i1177.photobucket.com/albums/...7/100_2312.jpg

Intake air heaters before or inside the filter are usually for cold starts, and (in newer diesels) for burning out the DPF.

Think I've said it before, cold air intake is generally preffered for diesels, but that is within reason, depending on the engine tune & fueling map.
I think ideally an intake that could maintain a constant temp year around would be best, and then adjust the tuning, intake, exhaust etc. around this particular temp range.
Getting more air into a diesel increases efficiency until the point is crossed where pumping losses start to pull the power curve back down.
Warming air up from below 0C will definately improve combustion efficiency, but once you get over 50C, then you will start to have a significant effect on the actual air mass going to the cylinder and this will have a major effect on both efficiency as well as power.
Absolute Zero is -273C, so if the same pressure & volume is maintained, going from 0-50C will be a decrease of about 18% air mass actually entering the cylinder.

Yes, the intake heater is for cold starts. My truck has a grid heater. It's an alternative to glow plugs for a cold start. Mine comes on whenever the intake manifold temperature upon turning the key on is below 66 deg F. I've never heard of it being used for DPF regens.

Warming the air is strickly to help the engine start, though--not to improve efficiency. A diesel is compression ignited, so when it's really cold, sometimes the pressure at the end of the compression stroke isn't enough to raise the temperature up to the point where it will ignite the first fuel injection. That's where the grid heater/glow plug comes in--warming the air prior to compression results in higher post-compression temperatures, therefore you can get ignition. This is also why higher compression ratio engines tend to start better in cold weather. Once you get the first few firing events to take place the cylinders, head(s), etc. warm up enough that the starting aids aren't needed anymore.

That's why I said colder air is alwars better--within reason (until you get down where you're really affecting ignition delays.

For every degree (F or C it doesn't matter) you increase intake air temp your EGT see the same increase.
With DPF you need as much EGT as you can get to burn off the soot, I wouldn't be surprized if some diesels fired up their intake heater to help burn off the DPM.

My solution, ax the DPF. On larger diesels it can take up to 17 liters, 4+ gallons of fuel, $16 worth of fuel, to torch the DPM off the DPF.
This is a great deal for the government, they get over $2 in taxes for 0 miles driven on your part every time your DPF lights up.

According to this site, normal exhaust gas temperatures in a turbodiesel are above 200°C, natural regeneration of the DPF happens at 400°-500°C, while 500°-600°C is needed for forced regen. Many things are done to get EGT that high, among them is warming of the intake air. Euromodder mentioned that a heater in the air filter box may be responsable for the higher temps in his intake he sees during regen.
Some TDs also have an intercooler bypass valve keep the post-turbo air warm, and sometimes restrict the intake to allow more EGR into the cylinders.

But this is all for DPF regen, not "normal" operation, so emissions in this case are more important than fuel consumption.

For modern cars the old rule of fuel in = power out still applies. The difference that air intake temperature makes is in the variable turbine geometry turbo.

When the engine is running the sensors feed back all the data to the ECU, which calculates the boost requirement based on an air density map. Basically the VGT is set to produce sufficient boost based on the fuel demand and the density of the incoming air. If the air is warm it will need more boost pressure to reach the density to ensure no smoke. Conversely if it is cold it will require a lower pressure.

This has a knock on effect on the pre-turbine exhaust pressure, and in fuel economy terms the amount of work the piston has to do to push the exhaust gasses out of the cylinder and past the exhaust turbine. If the turbine does not need to drive the compressor produce as much boost pressure then the amount of work done on the exhaust stoke is less. So..... lower air intake temperature (post intercooler) = less energy absorbed on the exhaust stroke.

Here you can find also some information on the topic:
The Common Rail - where maritime professionals meet • The forum area of www.dieselduck.net

I read that Vekke, My perception is that the hotter the air the more moisture it can hold. Cold air cannot hold as much water as warm air so cold air would contain less moisture.
I must of missed the point.

I would bank more on increasing the temperature of the fuel not the air.

Combined with a decent fuel water separator and filter there are many more possibilities/benefits with heated fuel.

Another good suggestion would be to preheat the motor and transmission with a block or blanket heater of some sort. That helps reduce the winter FE hit.

Cheers

Ive been watching my scangauge since reading this a few months ago and I can see no real difference at idle and my intake temperatures go up 10C or more when sitting still and there seems to be no change at all (there is scatter in the readings). Biggest two that I see are both Oil and Coolant making a big difference (even 10C there).