Fuel systems
Sat, 03/12/2011 - 09:37
A comment by unconventional rebel over in the general section, regarding higher winter fuel consumption has got me thinking. (incidentally, I think navy boy is most likely right on that particular question)
I would still like to know the effect of varying air density on fuel systems. On fuel injected systems and carburettor systems.
From the outset, am I right in believing that atmospheric pressure and air density are linked? Are they one and the same?
Do modern fuel injection systems measure air volume or air mass, as a flow rate?
Will a carburettor automatically account for varying air density, assuming it is linked to atmospheric pressure? I reckon a CV carb might, but what about a slide carburettor ?
If I start at the bottom of mt everest on my, er let's say 1977 Honda 400 four, will I need a spare set of needles, slides and jets for when I reach the top?
Anyone have the answers?
Sat, 03/12/2011 - 14:38
#2
Re: Fuel systems
Thanks jag
That's very good of you to answer. Your answer is extremely informative.
The map system and a cv carb seem very similar in that they both respond to the same thing, albeit in a mechanical way as opposed to electronically.
Presumably the maf sensor would be upstream of the injector, so as not to be upset by the fuel droplets?
The consequence of more or less water in the air is, I presume, that more or less fuel will be needed to compensate ie; where there is water, there can't be air?
Sat, 03/12/2011 - 16:44
#3
Re: Fuel systems
Gasoline and energy:
Low octane fuel has the same amount of energy per pound as high octane fuel.
The difference is in the burn rate. Low octane fuel burns “faster” than high octane fuel.
You want the fuel, when burning, to “push down” on the top of the piston. Not hit the top of the piston like a hammer. A high octane fuel allows engines to have high compression ratios because the burnt rate is slower so there’s less chance of the fuel, when burning, to hit the top if the piston like a hammer.
High octane fuel has additives to control the burn rate. We used lead in the old days.
These posh fuels suggest to me they have additives that aid in the fuel to change from a liquid to a gas. In most engines not all the fuel is burnt during combustion. They are much better now than they were at one time.
You are right pittsy, the MAF sensor is upstream of the intake. Usually right after the filter.
Water in the air I refer to a gas or humidity rather than rain drops.
Water in the right amounts has an interesting effect. WWII Spitfires had a water injection system in their engines to be used under conditions where the pilot needed a very great power boost for a short period of time (usually a few minutes at most.
JAG
Sat, 03/12/2011 - 16:06
#4
Re: Fuel systems
Electronic fuel injection and carbs:
Obviously carbs and fuel injection do the same thing in the end. They are fuel atomizers.
At a very basic level I try to think of an electronic fuel injection system as a carb that is spread out.
Fuel pressure is similar to the carb’s float level.
The TPS senor is similar to the carb’s accelerator pump.
The coolant sensor acts like the carb’s choke.
The MAP or MAF sensor acts something like the carb’s venture or a carb with a variable venture.
The injector is the carb’s jet system.
There is some overlap between sensors but it does help a little when diagnosing where one might look first.
JAG
Sat, 03/12/2011 - 18:11
#5
Re: Fuel systems
Jag Quote "WWII Spitfires had a water injection system in their engines to be used under conditions where the pilot needed a very great power boost for a short period of time (usually a few minutes at most)"
Usually when chased by a Fokker I would imagine!
(Messerschmidt most likely, but I used Fokker for greater comedic effect. Apologies to any germans watching. No offence intended)
I'd be interested to know why squirting water into your engine would make you go faster!
Sat, 03/12/2011 - 19:13
#6
Re: Fuel systems
“Usually when chased by a Fokker I would imagine! “
Very good choice pittsy.
My father in law was a Spitfire pilot in WWII in Burma. He has tons of great stories of his adventures through Europe, North Africa, Burma, India and China.
He flew many kinds of Spits. His favourite was the Mark V model. He liked the 20 mm cannons. He did manage to crash a Spit. There’s one at the bottom of the Indian Ocean as a result of the engine’s lubrication system failure.
He flew a few Hurricanes in Burma but said that they were in such bad shape than when he fired its guns, it slowed down.
By the way, if you have to bail out of a Spit, the best way is to first fly it upside down to get out.
When taxing out on the run way the nose was so high the pilot couldn’t see ahead. You needed some lucky guy sitting on the wing to direct you.
The Fokker was a great plane (BMW air cooled radial engine). It took a while for the Spit engineers to come up with something equal to or better.
Life expectancy of the engine with the water injection working I think was about 10 minutes. So you didn’t use it very often or very long.
Why water injection works is a good question. I wish I had a good answer.
JAG
Sat, 03/12/2011 - 19:23
#7
Re: Fuel systems
I believe Saab Turbos had water injection too. Bloke where I once worked had one, wish I'd listened now.
Maybe the water/steam raises compression?
Sat, 03/12/2011 - 20:15
#8
Re: Fuel systems
“Maybe the water/steam raises compression?”
You may be on to something sutty.
For the engine to make more torque (power) the combustion pressure usually has to increase. This would suggest that adding the correct amount of water somehow increases the average combustion pressure than without the water added.
Of course the obvious question is, if it works so well why don’t we see water injection on all bikes and cars?
One way we would tell if water was getting inside an engine was that the cylinder where the water or coolant was getting in was completely clean of carbon deposits.
In the old days we sometimes poured a small amount of water into the intake of the carb while the engine was running to try to clean out the carbon inside the engine. The engine would have to be hot and you poured the water in very slowly. The exhaust would become a big steam cloud. Probably a practice not recommended by the manufacturer.
We also used rice, but that only worked on Japanese cars.
JAG
Sat, 03/12/2011 - 20:35
#9
Re: Fuel systems
I'm not technical but there's some technical information on this website together with some interesting videos. When I had a K1 I tried to get a black hole exhaust of them but they were focussing on the new K1200RS stuff .. I'm shortly going to get a K1200RS so ...
Sat, 03/12/2011 - 23:01
#10
Re: Fuel systems
WOW dogfm,
What a great site!
Thanks so much for the link.
Sooooooooooooooo, a K1200RS is on the horizon. Hope you get on it soon and have yourself one fast little Fokker.
Thanks again,
JAG
Sun, 04/12/2011 - 11:09
#11
Re: Fuel systems
I'll second that!
Thanks for that great link. Extensive site!
Prior to clicking on the link I was thinking along the lines of "well water is hydrogen and oxygen. One burns extremely well(!) the other aids burning, so that must be the answer".
Nope! Couldn't be more wrong! The answer is the simplest explanation. It cools!
Picture the scene:
Sir Harry puzzling over how to extract more power to keep away from those pesky fokkers. Tea boy comes in with a cuppa. Looking over sir Harry's shoulder. "squirt some water in the engine sir"
Answer: "go away you silly boy!"
Tea boy leaves the room.
Sir H thinking "mmm. Might have to give that a try!"
The rest is history!
Well I like to think that's how it might have happened.
Sun, 04/12/2011 - 11:23
#12
Re: Fuel systems
Jag
Thanks for the tales of your father in law. Great stuff.
I read a book about the hurricane by Leo mckinstry a couple of months ago. A good read. I can recommend it. He mentions that those planes slowed down with all guns blazing.
Sun, 04/12/2011 - 13:56
#13
Re: Fuel systems
The right stuff:
I believe there was a movie called, “The right stuff”. It is about the type of people who make good astronauts. The Americans used fighter pilots in their early astronaut programs because they had the right stuff.
After listening to my father in law I can understand why. This amazing group of people had to be full of self-confidence, sharp witted and blessed with great eye sight.
He recalled one incident where one pilot challenged another with a wager for 1/10 of a penny that he couldn’t do an outside roll with a Spit. The fellow took the wager and won the bet.
If you ever want to know what real beauty is and sounds like, just watch and listen to a Spit on a low level flyby. My Lord what a beautiful sound that V12 makes.
JAG
![spit-8c[1].jpg](http://www.ashonbikes.com/sites/default/files/spit-8c[1].jpg "spit-8c[1].jpg")
Sun, 04/12/2011 - 16:18
#14
Re: Fuel systems
Hardly anyone looks on the technical forum. I reckon you might just get away with pasting a photo of a spitfire on a motorcycle site!
I mentioned a car once and nobody noticed that.
Sun, 04/12/2011 - 16:23
#15
Re: Fuel systems
Actually, it is relevant to the topic.
I wondered what effect different air density has on a carburettor. And a spitfire uses those I believe. And it flies quite high.......
Sun, 04/12/2011 - 18:46
#16
Re: Fuel systems
There's another reason water injection is such a major boost to power, it makes your petrol engine double up as a steam engine. The water enters the cylinder as a liquid (albeit in droplet and vapour form) but the heat in the cylinder turns it to steam, massively increasing the cylinder pressure, just as long as there isn't so much it douses the burn. Those pressures are huge - just ask James Watt - and they're in addition to the engine's max power, hence it doesn't last very long.
Carburettors don't really compensate for changing air density very well and what tends to happen as a bike gains altitude is the air thins but the fuel being drawn into the engine doesn't decrease proportionally, so the engine starts to run increasingly rich.
Spitfires used carburettors mostly I believe (although I think later ones had fuel injection, maybe JAG can help here) but the mixture was set manually by the pilot anyway during flight.
Mon, 05/12/2011 - 11:35
#17
Re: Fuel systems
Thanks Kevin for responding.
I went right to the horse’s mouth and asked Dave, my father in law, about Spits.
He is really quite a guy. Loves his Spits.
I asked him about Spit carburetors. He said they had several versions through the war. The very early versions had one serious problem that the German 109’s didn’t have. When flying upside down the Spit carb would go lean and the engine would stall. You then had to invert to right side up and try to restart your engine. Not a good thing when engaging a 109.
Another interesting problem was that sometimes the front wheel carriage would not come down when landing. The cure often was to fly the plane upside down and then lower the wheels. You couldn’t fly very long this way because the engine would quickly overheat.
A favorite trick on the Mark V’s was to fly very close and just under the rear wheel of another Spit with an inexperienced, inattentive pilot. If you got close enough to the rear wheel of the other plane with your prop, the wash from your prop would cause the rear landing wheel to shake.
When revving the engine hard before takeoff the Spit had a tendency to want to flip over. To stop this from happening they often used two female mechanics or ground crew to lie across the rear tails. He knows of two incidents where the Spit took off with one of the ladies still holding on to the tail. The pilots managed to get the ladies back safely.
As a little side note, he was present when the first early American helicopter was used in a rescue to get out wounded soldiers in WWII in 1944.
The wounded were deep in the jungles of Burma and deep behind enemy lines. No landing room for even a small light plane. The helicopter had very limited range and load capacity (about 150 pounds). Maximum height was about 500 feet. How the Americans accomplished the feat was truly heroic and amazing. Just accomplishing the logistics of getting and setting up fuel drops to get the helicopter there and back was a feat in its self.
They started out with three choppers in India. Only one made it to Burma. Two had mechanical problems.
They could only get one soldier out at a time but they did it.
It was code named Project 9.
From the internet:
Operational history
On 22–23 April 1944, U.S. Army Lieutenant Carter Harman of the 1st Air Commando Group conducted the first combat rescue by helicopter using a YR-4 in the China-Burma-India theater. Despite the high altitude, humidity, and capacity for only a single passenger, Harman rescued a downed liaison aircraft pilot and his three British soldier passengers.
They got all their boys out safely.
What a great movie it would have made.
Ordinary men doing extraordinary things.
JAG
Mon, 19/12/2011 - 21:27
#18
Re: Fuel systems
Anyone know about plasma spark plugs?
All hype or the next big thing?
Thu, 22/12/2011 - 18:14
#19
Re: Fuel systems
And thanks JAG for that, what amazing stories, I could read that sort of thing all day! And what a privilege getting them directly from someone involved, fabulous stuff.
Pittsy, I didn't know about plasma plugs, unless it's a slight distortion of something I did write about in MCN a couple of months ago, laser ignition. Ford and no doubt others are working on firing fuel-air mixtures in the combustion chamber using lasers. You'd have two laser beams shining into the combustion chamber and where they cross they 'spark' the mixture. It's not through heating it funny enough but a more complex process which creates something like a plasma. The advantage is this ignites the mixture from the centre of the combustion chamber rather than the edge, and the ignition timing is much more accurate. It uses a single laser generator and a series of spinning mirrors to direct and split the beam between the cylinders. There doesn't seem to be any problem with having a small window into the cylinder either.
The disadvantage is, if you have a misfire you can't fix it with a bit of old sandpaper...
Thu, 22/12/2011 - 18:21
#20
Re: Fuel systems
Thanks kev
Interesting stuff
A friend in the motor spares industry mentioned them to me. I've looked on google and there's something about plasma spark plugs on there. Not sure which type he meant. He seemed pretty sure they were just on the horizon.
Fri, 30/12/2011 - 17:01
#21
Re: Fuel systems
Does the Honda NC700 use EGR? (the JAZZ on which it is based seems to).
For that matter does any other motorcycle (or scooter)?
EGR increases efficiency yes? (or can be made to). As well as lowering certain emissions.
Fri, 30/12/2011 - 18:56
#22
Re: Fuel systems
The EGR valve in the automotive industry is used to lower Nox emmisions.
Nox emissions occur during that very high, very short duration, temperature spike at the moment the fuel mixture ignites.
The EGR valve lowers Nox emissions by lowering that momentary high temperature spike.
What the EGR valve basically does is, when opened, it allows a cooler gas into the intake (cooler compared to that high temperature spike). A gas that is also low in oxygen into the intake.
That gas is exhaust.
This re-entered (re-cycled) exhaust gas that is low in oxygen takes up space. As a result not as much fuel/air mixture can get in. The result is a lower engine power output.
To maximize the vehicle’s drivability when the EGR valve is used the valve is usually controlled not to open when the engine is cold, at startup, at idle or at full power.
It usually is open when the engine is warm, at light loads, at normal mid range engine speeds such as at normal highway cruising speeds. It is hoped that under these conditions the operator won’t notice the power loss.
Many vehicles do not use an EGR valve anymore. They get a similar affect by modifying the valve timing.
JAG
Fri, 30/12/2011 - 18:56
#23
Re: Fuel systems
Hi jag.
Thanks for reply.
I lifted this from wikipedia. There it makes claims for potential to increase efficiency as follows:-
The exhaust gas, added to the fuel, oxygen, and combustion products, increases the specific heat capacity of the cylinder contents, which lowers the adiabatic flame temperature.
In a typical automotive spark-ignited (SI) engine, 5 to 15 percent of the exhaust gas is routed back to the intake as EGR. The maximum quantity is limited by the requirement of the mixture to sustain a contiguous flame front during the combustion event; excessive EGR in poorly set up applications can cause misfires and partial burns. Although EGR does measurably slow combustion, this can largely be compensated for by advancing spark timing. The impact of EGR on engine efficiency largely depends on the specific engine design, and sometimes leads to a compromise between efficiency and NOx emissions. A properly operating EGR can theoretically increase the efficiency of gasoline engines via several mechanisms:
Reduced throttling losses. The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses.
Reduced heat rejection. Lowered peak combustion temperatures not only reduces NOx formation, it also reduces the loss of thermal energy to combustion chamber surfaces, leaving more available for conversion to mechanical work during the expansion stroke.
Reduced chemical dissociation. The lower peak temperatures result in more of the released energy remaining as sensible energy near TDC, rather than being bound up (early in the expansion stroke) in the dissociation of combustion products. This effect is minor compared to the first two.
It also decreases the efficiency of gasoline engines via at least one more mechanism:
Reduced specific heat ratio. A lean intake charge has a higher specific heat ratio than an EGR mixture. A reduction of specific heat ratio reduces the amount of energy that can be extracted by the piston.
EGR is typically not employed at high loads because it would reduce peak power output. This is because it reduces the intake charge density. EGR is also omitted at idle (low-speed, zero load) because it would cause unstable combustion, resulting in rough idle. The EGR valve also cools the exhaust valves and makes them last far longer (a very important benefit under light cruise conditions).[citation needed]
Fri, 30/12/2011 - 19:04
#24
Re: Fuel systems
Thanks pittsy,
Your report brings up things I had not considered.
It appears that when it comes to the EGR valve how well it is controlled is everything.
Thanks again,
JAG
Fri, 30/12/2011 - 19:49
#25
Re: Fuel systems
Jag, may I draw your attention to this line from the above text. " A properly operating EGR can theoretically....."
It's not cut and dried by any means.
What got me onto this in the first place was A) the fact I have pins sticking out of my toes and have a ZERO tolerance policy for daytime television. Unless it's repeats of bike racing on Eurosport. B) my inquisitive, sceptical nature.
So. I'm thinking Honda have made a big shout about lowering friction losses in the NC700. But these only account for about 5% of the total losses in a typical engine. Heat lost into the coolant is about 30%. Heat lost down the exhaust pipe is about 35%.
So why are we chasing 1% of 5% when we should be looking for 2 x (15% of 30%). Ish.
Fri, 30/12/2011 - 20:50
#26
Re: Fuel systems
"Reduced throttling losses. The addition of inert exhaust gas into the intake system means that for a given power output, the throttle plate must be opened further, resulting in increased inlet manifold pressure and reduced throttling losses.
Reduced heat rejection. Lowered peak combustion temperatures not only reduces NOx formation, it also reduces the loss of thermal energy to combustion chamber surfaces, leaving more available for conversion to mechanical work during the expansion stroke."
I thought those two point as interesting considering you comments about heat losses to the cooling systems.
I think we have commented before concerning energy losses to the exhaust and cooling systems. Looks like you have been doing some homework.
Turbo-charging will get some of those exhaust energy losses back.
The engine as we presently know it may require modifications from the use of metals like aluminum for the block, head, pistons and steel for the valves if you want to recover some of the coolant energy losses.
Really comes down to cost. How much are you willing to spend on a new bike to get another 20% savings on fuel?
You tell me. How much money would you save over say 3 years on your bike with a 20% fuel useage reduction?
JAG
JAG
Fri, 30/12/2011 - 21:07
#27
Re: Fuel systems
In regards to fuel mixtures and MPG.
What I find interesting is that it seems many bikes with RWHP measured graphs also include the torque curves. Usually these torque curves have a pronounced flat area or dip in torque output at about what the engine RPM is at typical highway speeds in their top gears.
One could argue that this dip in torque is intentional and could be aimed at improving MPG at normal highway cruising speeds.
The MT-01 is a prime example of such a torque curve at 60 to 65 MPH in its top 5th gear.
This is pure speculation on my part.
JAG
Fri, 30/12/2011 - 21:55
#28
Re: Fuel systems
Jag
I have noticed that these "curves" are not very curvey! You may be onto something there!
Heat loss. Ceramic and kryptonite you say. Nah.
We take all that damaging heat away from the engine and then...... Throw it all away to the atmosphere! Via the raditor. At least in a car we use it to keep warm.
Why can't we "harvest" it? (my first use of a "buzzword" for ages)
Fri, 30/12/2011 - 22:27
#29
Re: Fuel systems
MT-01 Torque Curve in 5th gear from 40 - 80 MPH
Below is a torque curve of the MT-01 in its top 5th gear from 40 to 80 MPH.
The torque values in ft/lbs are only based on the RWHP values.
Notice the dip in torque from 60 to 65 MPH.
It could also mean that the manufacturer is trying very hard to meet very strict emission standards and MPG standards by running the bike as lean as possible at normal cruising speeds. Too lean and performance and driveability suffers. This would be especially true at low load and partial throttle positions. How many bikes (Ducati) have stumbling and throttle response issues around these road speeds?
Interesting.
JAG
Sat, 31/12/2011 - 00:09
#30
Re: Fuel systems
Stirling Cycle Engine - Heat Engine
pittsy,
If you want to "harvest" all that heat consider the stirling cycle or heat engine.
It's older than the gas engine.
JAG
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Hi pittsy,
Question:
Do modern fuel injection systems measure air volume or air mass, as a flow rate?
In regards to American electronic fuel injected cars they use two basic sensors to calculate how much air is entering the engine.
#1 MAF sensor or mass air flow sensor (measures mass)
#2 MAP sensor or mass absolute pressure sensor (measures volume)
Some cars use both.
Both sensors help maintain the correct air fuel ratio under constantly changing operating conditions.
The ideal air fuel ratio is 14.7 – 1 or 14.7 pounds of air to 1 pound of fuel. Under heavy engine load the air fuel ratio may change to about 12 – 1.
A MAF sensor actually measures the weight over time of the air entering the engine. So it can tell the computer how much air in grams is entering the engine at any time. It does this in a very interesting way. The sensor has a wire with a small resistor in the center of the wire. The wire and resistor are placed across the diameter of the opening or inlet of the engine. The sensor sends a measured current through the resistor placed in center of the air stream of the inlet. The current flow through the resistor causes the resistor to heat up. The air rushing by the resistor tends to cool it down. The more air passing by the resistor, the more the cooling effect it has on the resistor. The current flow through the resistor changes with the temperature of the resistor.
A MAP sensor is basically a vacuum gauge. It is cheaper and usually smaller than a MAF sensor. The vacuum reading from the sensor tells the computer the engine load. The computer has programmed in look up tables to calculate, based on the throttle position sensor’s (TPS) position, how much air should be entering the engine at any one time.
On advantage of a MAF sensor is that it also senses the amount of water in the air or the air’s humidity. Moist air will cool the resistor faster than dry air. Have you ever noticed that you bike is different on cool humid days as compared to when the air is hot and dry?
A MAF sensor responds to altitude changes or barometric changes better plus ambient air temperatures (colder air is denser that hot air) better.
The TPS is an important sensor in both MAF and MAP systems. The TPS (throttle position sensor) tells the computer how much the throttle is open but just as important it tell the computer the rate of change or how fast the throttle is opening.
In summary, both MAP and MAF sensors do the job. I personally like a MAF system better. The computer uses this information to help calculate the correct air to fuel ratio and control engine ignition timing.
JAG
P.S. Why engines need a choke system when cold is another interesting question.
HINT:
The fuel that actually burns has to be directly exposed to air. In a drop of fuel from an injector or carbutertor, only the outside surface of the fuel drop burns. Ideally the fuel drop should change from a liquid to a gas before or during combustion in order for all the fuel to burn.
Of course the smaller the drop of fuel, the easier or quicker the drop can change to a gas. That's why fuel injectors have so many very small outlets.
In a cold engine that change from a liquid to a gas doesn't happen very well.
Many of the fuel droplets do not fully change to a gas. Since only the outside surface of the drop burns you need a lot more drops to keep the engine running.
To get a lot more drops of fuel you need a choke system when the engine is cold.
If you changed your bike to natural gas or propane you would find you would not need a choke system. You may need a faster cold idle speed only to compensate for the oil thickness when cold.