Compression ignition

[Lloyd-ss]

I remember Mr.Hansen saying in one of his diesel videos that, even though he has been asked many times, he does not give drawings or much "detailed" information about his engines, because if he does that, people will ask more and more questions, and will want him to diagnose why their engine doesn't work even though they built it just like he told them too.
He seems to be taking the approach that is part of the definition of a Patent, that it needs to have only enough information such that someone "trained in the art" of the broader patent category, should be able to produce similar results. Basically, "here is what I did, but you will have to figure out the special techniques yourself."

My apologies if I am wandering around too much. Like the old guy with the shopping cart stopped in the middle of the aisle, blocking everyone's progress.
Lloyd

 

[HMEL]

Thank you for the discussion.

I suppose if I build a "true" diesel of sorts and used a commercially available injector I could scale the model to suit. Right now its a pipe dream.
If only Mr. Find Hansen would let us in on some of his secrets but if can build small models that work I am sure over time I could theoretically do the same.

In his build titled Build a true model A frame engine in three parts he lays out how each system is designed. I did not see any secrets. He shows how the system are configured and gives the basics of the design parameters if one listens. What he does not do is give drawings but the concepts are well described including pictures of how he bench tested his injectors. However, one would have to make their own drawings based on his concepts. I would have gladly given it a shot except I do not have enough tooling to do the cams and smaller parts. I do understand that making those drawings based upon the described concepts is a challenge. Not sure where the castings come from but I assume they are available and if they are it makes it easier to scale the other components. I suspect he did the bench work first then made drawings of the things that worked, more of a hands on engineer and probably hates documentation.

 

[GRAUBELE]

A little "off topic" because of the engine size, but still relevant to the topic.
The engine of my original vintage tractor is a DEUTZ Diesel (type MAH-914)
with a displacement of 1.100 cc and 12 hp.
Data sheet values:
Compression ratio 1:20
Compression value 26 kg/cm2 (~25.5 bar)
Release pressure of the BOSCH injection nozzle 120 kg/cm2 (~117.7 bar)
It is said, I don't know for sure, that the piston brings the air in the cylinder to around 700°C,
when compressed to start the engine.

 

[GreenTwin]

In his build titled Build a true model A frame engine in three parts he lays out how each system is designed. I did not see any secrets. He shows how the system are configured and gives the basics of the design parameters if one listens. What he does not do is give drawings but the concepts are well described including pictures of how he bench tested his injectors. However, one would have to make their own drawings based on his concepts. I would have gladly given it a shot except I do not have enough tooling to do the cams and smaller parts. I do understand that making those drawings based upon the described concepts is a challenge. Not sure where the castings come from but I assume they are available and if they are it makes it easier to scale the other components. I suspect he did the bench work first then made drawings of the things that worked, more of a hands on engineer and probably hates documentation.

I think all of Find's engines are barstock construction.

In my opinion, I think Find gives plenty of good information about what he did, and how he did it, and more information that I would normally expect from many/most model diesel engine builders.

I think Find is a bit of a freelance type builder, as you can see from him trying one connecting rod, having it bend, and then increasing the size of a new connecting rod. He really has done some impressive work in my opinion, with great attention to very small details.

There is no way I would attempt to build a diesel that small, even though I don't consider Find's engines "small".
I think I would start with a bore in the 2.0" to 2.5" range, just to try and make the injector parts as large as possible.
I would build a diesel just like a full sized 2-stroke diesel, ie: with massive flywheel(s), massive bearings, very good lube system, and a very strong rigid frame.

My dad had a Witte diesel (I think that was the brand), with about a 4" bore, and it was a beast of an engine, extremely heavy, but it would run at rated load all day every day, without any problems.

Find uses a flat top piston, and does not seem to have any problems with combustion due to that.
I seem to recall that Find's compression ratio is 21:1, and with large quality bearing surfaces on all the moving parts, I think this would easily be achieved.
.

 

[minh-thanh]

here are some fun facts from thermodynamics, compression ratio, pressure ratio PSI, and Temp, for gasoline engines in the 6 to 12 CR range and diesel around 20
6:1 12:1 166 psi 625-F (for the non-imperialists, ~12-bar, ~330-C)
12:1 32:1 462 psi 972-F
20:1 66:1 960 psi 1780-F (ditto, ~66-bar, ~970-C)

Where did you get that information? I want to learn more....

 

[GreenTwin]

Also, I believe(?) that good atomization is easier with a lower viscosity liquid, so am ready to believe that kerosene worked better than diesel for Hansen ?

Good atomization of fuel is more complex than one may imagine.
From a white paper by a Delvan burner nozzle engineer, smaller atomization does not necessarily make for a hotter or cleaner burning fuel.

And as I recall, higher viscosity fuel has a higher flow rate through the same nozzle as lower viscosity fuel.

I will try to attach the white paper.
Not exactly an injector, but perhaps some similarities.

And regardless of the forumulas/math, isn't it a well understood fact that diesel or kerosene that is injected into a cylinder with a 21:1 compression ratio will automatically combust ?
Seems like we are arguing semantics.

.

 

[Kegan]

In his build titled Build a true model A frame engine in three parts he lays out how each system is designed. I did not see any secrets. He shows how the system are configured and gives the basics of the design parameters if one listens. What he does not do is give drawings but the concepts are well described including pictures of how he bench tested his injectors. However, one would have to make their own drawings based on his concepts. I would have gladly given it a shot except I do not have enough tooling to do the cams and smaller parts. I do understand that making those drawings based upon the described concepts is a challenge. Not sure where the castings come from but I assume they are available and if they are it makes it easier to scale the other components. I suspect he did the bench work first then made drawings of the things that worked, more of a hands on engineer and probably hates documentation.

Being a novice plans would be wonderful. However, you make many valid points. I admire his work and have no grudges against him. My biggest frustration is getting my lathe up and running. I am itching to start turning something. Thanks for the post

 

[minh-thanh]

here are some fun facts from thermodynamics, compression ratio, pressure ratio PSI, and Temp, for gasoline engines in the 6 to 12 CR range and diesel around 20
6:1 12:1 166 psi 625-F (for the non-imperialists, ~12-bar, ~330-C)
12:1 32:1 462 psi 972-F
20:1 66:1 960 psi 1780-F (ditto, ~66-bar, ~970-C)

Please tell me where you got this information? source ? link ???

Google will tell you the flash point and self-ignition point of each fuel you use, how are they different? their purpose??, gasoline, kerosene, diesel.....

 

[GreenTwin]

Best watched with the closed captions turned on.

 

[GreenTwin]

here are some fun facts from thermodynamics, compression ratio, pressure ratio PSI, and Temp, for gasoline engines in the 6 to 12 CR range and diesel around 20
6:1 12:1 166 psi 625-F
12:1 32:1 462 psi 972-F
20:1 66:1 960 psi 1780-F (ditto, ~66-bar, ~970-C)

Atmospheric pressure is about 14.7 psi.

For the first line, if the "compression ratio" is 6:1, then that is the reduction in the volume inside the cylinder when the piston travels from bottom-dead-center to top-dead-center.

The pressure difference is the difference between the pressure inside the cylinder at TDC and atmospheric pressure, so 166 / 14.7 = approx. 12:1 (pressure ratio).

I would guess the PV=mRT equation or something similar will yield the temperature at the compressed pressure, ie: 625 F @ 166 psi.

The autoignition temperature for kerosene is about 410 F.
The autoigntion temperature for typical #2 automotive diesel is in the range of 489-545 F.

Using Peter's info, it should be possible to make a functioning diesel engine that operates on #2 diesel with perhaps 14 or 15:1 compression ratio.
Cylinders, rings, valves, etc. may be prone to leakage, and the walls of the cylinder and the cylinder head will also absorb heat, so I assume that is why a typical diesel engines seem to operate in the 18:1 to 21:1 compression ratio (roughly).

Low compression can also make diesels difficult to start at their parts get worn, and thus the can of ether that many diesel users keep on hand as the engine hours accumulate, and especially with cold weather starts.

Cold starting would probably also require a bit of excess compression other than the theoretical minimum for autoignition of diesel.

Since you are injecting diesel or a similar fuel at a precise moment (for a diesel engine with an injector), there is no danger of the fuel pre-detonating before TDC.

For a gasoline engine, if the fuel does not have sufficient octane, you can have pre-ignition of the fuel from autoignition before the sparkplug has a chance to fire.

I seem to recall that a higher compression ratio will yield higher torque, but I am not positive of that.

Correct me if I am wrong, but I think the above assumptions are correct.

.

 

[minh-thanh]

Let him answer me.
Please tell me where you got that information? source ? link ???
It is not necessary to answer all of that information
Just need this information :
6:1 12:1 166 psi 625-F (for the non-imperialists, ~12-bar, ~330-C)

 

[GreenTwin]

Obviously we have an open public forum here, and so anyone/everyone is welcome to comment on a topic.
If someone wants to have a private conversation with another member, we have a private message system for that purpose.

.

 

[minh-thanh]

Ok, understand
You, Please explain, prove...or in any way you can :
6:1 12:1 166 psi 625-F (for the non-imperialists, ~12-bar, ~330-C)
Please
Most important: 330 degrees Celsius !!

 

[Klrskies]

We might also consider that dynamic forces will act upon actual compression ratio, drawing it down just prior to the instant ignition is required. The compressed air's molecular volume being reduced from the cooling effects of metals enclosing the combustion space and the cooler fuel being injected in fine particulates that absorb heat from the air prior to ignition.

 

[Lloyd-ss]

Where did you get that information? I want to learn more....

Minh-Thanh, I hope Peter doesn't mind me stepping in here, but I will do my best to present the math for the thermodynamics of air compression.
First, an assumption regarding the type of compression must be made. With fast compression as in an engine, the process is normally considered to be adiabatic, such that as the air is compressed, all of the heat of compression stays in the compressed air, and none is lost to the cylinder walls. (This assumes that the heat lost from an engine is from combustion, not the compression.) An isothermal compression process is where the air is slowly compressed such that all of the heat of compression is lost thru the cylinder walls. Full isothermal compressions are rare, and the compression process is often somewhere between adiabatic and isothermal.
Confusing, yes, but we will go with full adiabatic compression.

Finding the final pressure and temperature is a 2 step process.
Here are the terms:
Starting volume V1 and final volume V2. we will use cc's.
Starting and final pressure P1 and P2. we will use Bar.
Starting and final temp T1 and T2. we will use degrees Kelvin.
Specific heat ratio for air, called gamma, is 1.4 for air (adiabatic process) but can vary all the way down to 1.0 for a true isothermal process. We will use a gamma =1.4

I will write the formulas as in an excel spreadsheet., but with extra parentheses for clarity.

Step 1. starting volume V1 and final volume V2.
This is easy. For a diesel at 20 to one compression, say the volumes are:
V1=20cc and V2=1cc
CR= V1/V2=20

Step 2. starting pressure P1 and final pressure P2.
This is more difficult. P2 varies with the value of gamma.
P2=(P1*(V1^1.4))/(V2^1.4)
Let's say P1is one Bar (14.7 psi)
P2=(1*(20^1.4))/(1^1.4)
P2= (1*(67.17)/(1)
P2= 67.17 Bar (974 psi)

Step 3. starting temp T1 and final temp T2. (must use the Kelvin scale)
You must choose a starting air temp. Let's call it 90 deg F = 305 deg K
T2=(P2*V2*T1)/(P1*V1)
T2= (67.17*1*305)/(1*20)
T2= 1012K (1362F)

Please note that T1 starting air temp and the value of gamma can have quite an impact on the final temp T2. That is why sometimes the data from different charts might not appear to match.
I hope I didn't make too many typos, but please let me know if I did.
Peter, I hope you concur and don't mind me hoping in here.
Lloyd

 

[minh-thanh]

Hi @Lloyd-ss !
Thank you, at least you gave me the formula to calculate
Thank you very much !

But to me this information is completely wrong :
"6:1 12:1 166 psi 625-F (for the non-imperialists, ~12-bar, ~330-C)"
330 !??? what ??
It is completely wrong with the principle of 2-stroke and 4-stroke engines with ignition
Because as far as I know: In 2-stroke and 4-stroke engines, the fuel mixture is compressed and at a temperature MUST be lower than the self-ignition temperature of the fuel. That's why it requires ignition and requires a low flash point
And I'm sure of one thing, it will never reach 330 degrees Celsius with 12:1
Self-ignition point of gasoline : varies from 247°C to 280°C

 

[Mechanicboy]

Let him answer me.
Please tell me where you got that information? source ? link ???
It is not necessary to answer all of that information
Just need this information :
6:1 12:1 166 psi 625-F (for the non-imperialists, ~12-bar, ~330-C)

Also you need the ideal gas law: adiabatic compression to find the temperature of compression if the volume, pressure and moles is known.

https://www.calculatorsoup.com/calculators/physics/ideal-gas-law.php

 

[Lloyd-ss]

Hi @minh-thanh
Auto ignition temperature is the lowest temperature that a proper air fuel mixture MIGHT ignite, not the temp that it WILL ignite at. The speed of compression, and the high pressure within the cylinder make the auto ignition temperature difficult to predict. I think you are asking why doesn't the heat of compression always cause pre-ignition.
Good question, LOL. I am reading but it is confusing and I can't find a helpful answer.
The high heat of compression temperatures from Peter and myself are theoretically correct. Quite the conundrum.
Lloyd

EDIT 5-9-24 by Lloyd
This might be part of the answer.

The pressures need to be in absolute pressure.
Therefore, P1 might be 0.5 bar instead of 1 bar. That will make a big difference in the final pressure P2 and final temperature T2.

 

[NapierDeltic]

Hi, I don't know if I should enter such hot discussion. I have read some engine books, most appearing in 1950-1990.

First comment, as an interesting example for the case. Free piston engines were (and still are) one of St. Graal of IC engines.

At the level of 70', Sigma(France) and Fairbanks-Morse - if I correctly recall - (USA) had already built notable mature diesel units at 1000HP level.
Ford and GM (among others) had further tried to downsize these units Their professional conclusion was, at the same technical level, practical free piston units below 90mm bore could not be built due to cycle-by-cycle consistency (or inconsistency).
After 2010, with the aid of electronic control (also new materials involved), free piston engines micron sized , with application in human exoskeleton powering (not to mention other applications) were studied.
Conclusion: where, in this range, your abilities are? To know what are you aiming for.

Main subject: diesel engines.
I have read a meaningful 1960' Soviet Union/Russian - all IC - engine book (some time ago). At that moment Russians were thirsty to absorb - and both to diffuse technical info. It had a BIiig chapter about diesels, starting with semi-diesels.
Conclusion 1 - semi-diesel is a true diesel, although its compression ratio can be very low.
Conclusion 2 - (explicite) was - efficiency of diesel engines; both as diesel cycle and engine flexibility - is proportional to compression ratio. There was more of that , there, off course!

I have read 1980' books about diesels . There were 2 main conclusions:
Compression ratio is main factor in modern engines.
Second factor is reducing ignition delay (time) in modern high speed diesel engines. Ignition delay means fuel that accumulates in ignition chamber and explosively starts burning. This first stage means an incontrollable stage of fuel burning, with explosive -like behavior. If this stage can be controlled (and reduced), diesels would run much smoother. Delay is intimately conditioned by forming intermediary chemically reactive compounds from fuel at high temperature and presence of oxygen atoms around, close, to react with.
There are several means to reduce this delay -first being hot bulb (semi-diesel) engines. You just can't control ignition moment/cycle by this method.
In 40's-70's, ignition delay was reduced by creating additional turbulence, using various designs of secondary injection chambers and communication nozzles. Those provided smoother burning at the expense of efficiency losses due to higher gaseous friction losses and thermal losses coming from increased turbulence.
There are lots of other means of reducing ignition delay, (like higher injection pressure used in nowadays common rail engines, higher fuel temperature, hot-spots, different fuels, pilot injection.....). Opportunities are numberless and already approached paths are numberless.
My final conclusion: Either you want to be a pathfinder, or, if you want to achieve something easier, you have to find a balance between older designs; which are more precision machining tolerant, and newer designs that benefit from technological acknowledgements. Either ways you should read old books!

Second is that theory goes always behind experimental and only tries to adjust its formulas to match experimental results, reconsidering previously ignored factors. For processes with enough pool of data you can predict the evolution of the system; for those which are quite different you have to rely on available data in similar cases and on your own experiments.

 

[minh-thanh]

Hi @minh-thanh
Auto ignition temperature is the lowest temperature that a proper air fuel mixture MIGHT ignite,

That's right .
But with a compression ratio of 12-1 and a temperature of 330 degrees Celsius, it is too high compared to the auto-ignition temperature of gasoline - 280 degrees Celsius.
And with that 330 degrees Celsius, 2-stroke and 4-stroke engines will not need an ignition system and we may not be able to use it.
Still saying: I don't believe it - 330 degrees Celsius

@Lloyd-ss But at least you gave me a formula to calculate...Thank you for that.
Personally, I don't know much about engines and engine-related calculations, so I'll stop here.