ESE's works engine tuner

[F5 Dave]

Disco is dead Neil.

Oh sorry. Not those Gibbs.

[Frits Overmars]

What should I say! Something that is affected by length but not by surface. I guess Isaac did not leave the building based on how you write. the only thing I can think of is sound but have a hard time applying it to something meaningful (could be something about Isaccs third). You have me by the balls on this one! What is the point of doing something if you do not understand why. Thanks for the thought exercise Frits.

Muhr, I have the utmost respect for the work of Sir Isaac Newton and I certainly do not deny the existance of friction, but inertia is a different animal and my point was that it may be easier to understand its effects if you leave friction out of the equasion for now.

[Muhr]

Muhr, I have the utmost respect for the work of Sir Isaac Newton and I certainly do not deny the existance of friction, but inertia is a different animal and my point was that it may be easier to understand its effects if you leave friction out of the equasion for now.

Teriks has also tried to make me understand this by pm, but the token has not fallen down yet.
That we have a mass to accelerate it is obvious.
That we have an area on the intake that the air must enter through that I also understand.
But that if we extend it 50mm with a piece of pipe and hence get a higher inertia in that acceleration without friction being the factor there, you have lost me.
In my head I think that atmospheric pressure does not care that it only has one way in or longer, as long as it is not exposed to an area change.
Thanks for trying!

[Peljhan]

Thank you all for nice lesson
Best way will be to install rotodisc and try some variations on dyno.

Flettner, I can't make Gibbs now as I have allready made engine casings. (actually my friend with his CNC skills). Here are some pics.

Frits, I am using 175° now with my pistonported Tomos D6, with 2 transfers and butterfly exhaust. It is making 14HP on back wheel and 142km/h at Rijeka-Grobnik racetrack.

Wobbly, as I have 2 outputs on my Zeeltronic for solenoid powerjet, I want to install one anyway. Some advice, where can I get appropriate-decent one? Thanks.

[andreas]

Now we don't leave a man behind. It is obvious that there is a mass, and the mass gets greater the longer the duct. Also the pressure difference is the same, then Newton just say: delta p= force/area, and acceleration=force/mass.

[Frits Overmars]

Now we don't leave a man behind. It is obvious that there is a mass, and the mass gets greater the longer the duct. Also the pressure difference is the same, then Newton just say: delta p= force/area, and acceleration=force/mass.

I fully agree, Adreas; I'm just writing it down step by step.
Duct volume V = cross flow area A * duct length L
The mass m in our duct is proportional to the duct volume V
m ≈ V
m = A * L
The pressure differential p over this duct exerts a force F= p * A upon mass m
acceleration a is force / mass ;
a = F / m
a = (p * A) / (A * L)
a = p / L
In English: the acceleration of a mass in a duct is proportional to (pressure / length) . If you double the length, the rate of acceleration will be halved, and vice versa.


While we are at it, let us take a look at the amount of mass that is moved through the duct in a given amount of time.
First, let's make some assumptions in order to keep things simple (my hobbyhorse, as y'all may have noticed).
1: The pressure differential over our duct is constant (in reality it would drop because of mass moving from the high-pressure side to the low-pressure side of the duct).
2: The duct ends in a port which is fully opened during t seconds, after which it is suddenly closed.
The length of the gas column that passes through the port, is ½ * (acceleration a) * (time t)²
Now if we compare a duct with length L to a duct with a length 2L the acceleration in duct L will be twice as high as the acceleration in duct 2L, as we have seen above.
This means that with the same pressure differential and the same amount of open port time, the long duct will fill the cylinder only half as well as the short duct. It's a great reason for using a short inlet duct which allows us to use a short opening time.

[Muhr]

I fully agree, Adreas; I'm just writing it down step by step.
Duct volume V = cross flow area A * duct length L
The mass m in our duct is proportional to the duct volume V
m ≈ V
m = A * L
The pressure differential p over this duct exerts a force F= p * A upon mass m
acceleration a is force / mass ;
a = F / m
a = (p * A) / (A * L)
a = p / L
In English: the acceleration of a mass in a duct is proportional to (pressure / length) . If you double the length, the rate of acceleration will be halved, and vice versa.


While we are at it, let us take a look at the amount of mass that is moved through the duct in a given amount of time.
First, let's make some assumptions in order to keep things simple (my hobbyhorse, as y'all may have noticed).
1: The pressure differential over our duct is constant (in reality it would drop because of mass moving from the high-pressure side to the low-pressure side of the duct).
2: The duct ends in a port which is fully opened during t seconds, after which it is suddenly closed.
The length of the gas column that passes through the port, is ½ * (acceleration a) * (time t)²
Now if we compare a duct with length L to a duct with a length 2L the acceleration in duct L will be twice as high as the acceleration in duct 2L, as we have seen above.
This means that with the same pressure differential and the same amount of open port time, the long duct will fill the cylinder only half as well as the short duct. It's a great reason for using a short inlet duct which allows us to use a short opening time.

Thanks Frits now I understand where we went in different directions in this.
You write:
Duct volume V = cross flow area A * duct length L
The mass m in our duct is proportional to the duct volume V


As I understand the equation above, the air in the intake is a mass that is moved with the atmosphere outside. And if you move it twice the distance or need to do it half the time, double the force / time will be required.

This is what I have in my head when I think about it and calculate.
I see the air in the intake as part of the atmosphere with its restrictions that escalate with velosity to the maximum allowable flow is reached. which in this case unfortunately will not be linear
I reason like it's the same atmosphere in the box as outside until you put on a lid.

I have always thought like this:

R = ½ρCAv2
So I calculate with a velocity (v), the density (ρ) of air and area (A) on the intake and a coefficient of drag (C) (in this case friction)

[Flettner]

Thank you all for nice lesson


Flettner, I can't make Gibbs now as I have allready made engine casings. (actually my friend with his CNC skills). Here are some pics.

.

The sliding Gibs live in the valve cover, not the engine casing. Can be retro fitted to any rotary valve twostroke, just need the appropriate valve cover.

Nice machined case set by the way.

[wobbly]

The solenoid used on the later Dellorto magnesium race carbs was , I believe , a standard part used as an idle air bypass valve on a small Fiat Carburettor ( Weber )
The same thing turned up on Keihin carbs for MX bikes and aslo Honda RS125 98+ Keihin SPJ.
I have also used the Mikuni solenoid kit sold by Allensperformace .uk - very expensive.

[TZ350]

.
More from the genius of the Two Stroke Stuffing workshop.
.

[andreas]

If someone like a lower intermediate battle, I usually stay up late on Lichess.org as Lansandreas.

[lohring]

While we're on the topic of small, high power glow ignition engines, some of you may be interested in a series I wrote about the development and construction of high power model engines. It's an attempt to preserve the heritage of a dying breed. Glow plugs, a disposable item, are costing $15+ US dollars these days. I still have memories from the late 1950s of screaming control line speed engines fueled with shoe polish smelling nitrobenzene in exotic mixtures with names like Missile Mist. I hope there is enough information in these articles for an ambitious person to design and build these engines. Unfortunately, I doubt that they live in English speaking countries. I owe a lot of my understanding to several of the members of this forum. Thanks.

Links are below:


namba.com/content/library/propwash/2018/october/14/ History


namba.com/content/library/propwash/2019/april/24/ Modern Piston & Liner Construction


namba.com/content/library/propwash/2019/october/4 Cylinder Head Design


namba.com/content/library/propwash/2020/april/4/ Tuned Pipe Design


namba.com/content/library/propwash/2020/October/4/ Port Design & Scavenging


namba.com/content/library/propwash/2021/march/16/ Mechanical Design


Lohring Miller

[Frits Overmars]

While we're on the topic of small, high power glow ignition engines, some of you may be interested in a series I wrote about the development and construction of high power model engines. It's an attempt to preserve the heritage of a dying breed. Glow plugs, a disposable item, are costing $15+ US dollars these days. I still have memories from the late 1950s of screaming control line speed engines fueled with shoe polish smelling nitrobenzene in exotic mixtures with names like Missile Mist. I hope there is enough information in these articles for an ambitious person to design and build these engines. Unfortunately, I doubt that they live in English speaking countries. I owe a lot of my understanding to several of the members of this forum. Thanks.
Links are below:
namba.com/content/library/propwash/2018/october/14/ History
namba.com/content/library/propwash/2019/april/24/ Modern Piston & Liner Construction
namba.com/content/library/propwash/2019/october/4 Cylinder Head Design
namba.com/content/library/propwash/2020/april/4/ Tuned Pipe Design
namba.com/content/library/propwash/2020/October/4/ Port Design & Scavenging
namba.com/content/library/propwash/2021/march/16/ Mechanical Design

Thank you for this comprehensive overview Lohring.
It was a pleasant (and flattering) surprise to encounter the methanol-burning MB40 engine, although it's not even a boat engine .

[Flettner]

If one was to be looking at a 24 / 7 intake system, 125, what length would the intake tube need to be???

[andreas]

If one was to be looking at a 24 / 7 intake system, 125, what length would the intake tube need to be???

I've written down a note from Wobbly, it says 125 mm including end correction, to the reeds approximated opening point, is in tune at 12000 rpm. Probably there is more science to it for a 24/7.
So, I forgot How many Reflections/inversions that is, and then the Helmholtz? Basically I ain't got a clue.