tips for designing my own diesel engines

[ruben]

hello, good afternoon I want to design a diesel engine model but I don't know how to start designing I need advice on engine materials, specifically piston, cylinder head, connecting rod, crankshaft liner, cylinder, block I would also need help to design the block, cylinder, head, crankshaft, piston The one from which I got the measurements (diameter, stroke, piston length, flywheel weight) is from the Opel Z17DTJ engine. I don't know if the engine model will be of any use (only one cylinder). Any idea is good and welcome to create the plans thank you

 

[minh-thanh]

Hi
Materials: similar to another model engines - piston: 6061, 7075, gang - cylinder (engine and pump): cast iron, steel - connecting rod: aluminum 6061, 7075, steel -.....

"tips for designing my own diesel engines"​

I don't know, but I will say what I know from my experience and note: I am not a professional in engine design and other things, just an amateur.
As I asked you before: have you ever built an engine and I don't have an answer from you so it's hard to know your experience and knowledge, so I will say some basic things.
For me when designing an engine I have to base on what I can do, or at least based on my experience and judgment that I can do. With any engine I have done, the Cylinder is the first and most important part and then there are other parts that I can do to make sure the engine can run
For example: with a 2-stroke or 4-stroke engine - ignition, I can design it with a cylinder diameter I can do 2, 3, 4, ....12...14...mm but with the spark plug, how can I ensure its insulation with such a small area? With a cylinder that is too small, it is impossible at least for me,. so what about a larger cylinder like 14, 16 mm: it is ok but the spark plug seems quite big compared to the cylinder head....
What about diesel engines (injectors)? It's similar, but it also depends on the amount of fuel injected into the cylinder. And it is determined by the diameter of the fuel pump cylinder and the lunger stroke
That means I have to determine the diameter of the pump cylinder that I can make or rely on experience to know how small I can make it in mm and from the amount of fuel I will calculate the diameter of the engine cylinder, stroke, length of the cylinder, ....
The position of the gear, crankshaft, camshaft .......
A complete engine requires all the parts to be combined into a unified assembly
For example, the crankshaft you cannot use the parameters of a 4-stroke engine with a compression ratio of 6-1 for a diesel engine crankshaft with a compression ratio of 20-1 or use a 10 cc diesel engine crankshaft for a 50 or 100 cc diesel engine ...
It is difficult to give you a useful "tip"
Most useful: Start with what you can do

 

[ruben]

How to determine the diameter of the fuel pump cylinder and how to calculate the bore and stroke of the engine from the amount of fuel?

 

[minh-thanh]

Based on Roger B's calculation and actual results: a 10 cc diesel engine needs 1 mm3 of fuel (max)
It is difficult to give an exact fuel volume for a 10 cc volume, it depends on the tolerance between the plunger and the cylinder, the response (closing and opening) of the ball valve compared to the amount of fuel is too small and the time is fast, with the inlet and outlet valves being ball valves, the problem will be double, the force of the injector spring.... So let's choose a 10 cc engine that needs 1 mm3 of fuel (max)
---- Choose the engine volume you want to make (10, 15 or 20 ...cc) (****)
Fuel volume formula:
V = 3.14 * r * r * stroke ( r = radius of the cylinder )
Unit of measurement
r, stroke : mm, V: mm3
-- Choose diameter for the smallest pump cylinder that you can do - If the diameter result is too small beyond your ability, go back (****) to re-select the engine volume
=>The smaller the diameter, the longer the Plunger stroke, which allows you to adjust the fuel quantity better
Engine volume calculation formula
V = ( 3.14 * r * r * stroke ) / 1000
Unit
r, stroke: mm, V: cc
Select the engine cylinder diameter you want to do
---> With the volume and cylinder diameter, you calculate the piston stroke
The smaller the diameter, the longer the piston stroke, which allows you to adjust the compression ratio (change the combustion chamber volume) more easily

 

[ruben]

hello

a question
Is there a formula to create plunger fuel pumps and to make it work with the pressure you want?

 

[ruben]

hello

Would there be a formula to calculate the diameter and stroke with a compression ratio of 23:1

thank you

 

[ruben]

Based on Roger B's calculation and actual results: a 10 cc diesel engine needs 1 mm3 of fuel (max)
It is difficult to give an exact fuel volume for a 10 cc volume, it depends on the tolerance between the plunger and the cylinder, the response (closing and opening) of the ball valve compared to the amount of fuel is too small and the time is fast, with the inlet and outlet valves being ball valves, the problem will be double, the force of the injector spring.... So let's choose a 10 cc engine that needs 1 mm3 of fuel (max)
---- Choose the engine volume you want to make (10, 15 or 20 ...cc) (****)
Fuel volume formula:
V = 3.14 * r * r * stroke ( r = radius of the cylinder )
Unit of measurement
r, stroke : mm, V: mm3
-- Choose diameter for the smallest pump cylinder that you can do - If the diameter result is too small beyond your ability, go back (****) to re-select the engine volume
=>The smaller the diameter, the longer the Plunger stroke, which allows you to adjust the fuel quantity better
Engine volume calculation formula
V = ( 3.14 * r * r * stroke ) / 1000
Unit
r, stroke: mm, V: cc
Select the engine cylinder diameter you want to do
---> With the volume and cylinder diameter, you calculate the piston stroke
The smaller the diameter, the longer the piston stroke, which allows you to adjust the compression ratio (change the combustion chamber volume) more easily

and for the compression ratio

 

[ninefinger]

Fuel Pump
The fuel pressure will be determined by the injectors opening pressure, as the diesel is not compressible. If the pump outlet is blocked the pressure will rise to be equal to the force applied divided by the area of the plunger (or more likely something will break!), of course there are always efficiency losses. So in general the formula for the pump is knowing how much fuel will need to be delivered, and having enough margin to accommodate the losses (pump displacement plus margin for leakage).

Compression ratio
For a 4 stroke the compression ratio is simply the displacement (area x stroke) plus the combustion chamber volume, divided by the volume of the combustion chamber at top dead center. (i.e. initial volume between the piston and head and final volume between piston and head). The harder part is figuring out the combustion chamber volume - both theoretical and the actual volume as built due to it usually not being a basic geometrical shape.
A 2 stroke is more complicated as the port positions need to be known as the full piston travel is not representative of the volume that will be compressed.

For designing an engine - I would determine your desired displacement first (can be approximate based on other similar engines power outputs), and then figure out if you want an over square (piston diameter is greater than stroke) or undersquare arrangement (piston diameter is less than stroke) depending on the application, and then can figure out bore and stroke and pump requirements. Oversquare is typical of a high rpm engine, where as very undersquare would be like the Find Hansen engines (20mm diameter x 40mm stroke) with lower rpm but higher torque for same displacement. Seeing as you have been asking about Diesels I would expect that you are going to be looking at undersquare.

These are all good questions, but at the end of the day, actually putting a cutter to metal on an engine you designed without having any previous engine design experience is going to be a very difficult journey. I don't want to discourage you and say impossible, but if you don't currently understand the engine theory, then I would suggest getting familiar with many more existing designs, analyzing them and understanding the various differences and why they have different performances. I would also suggest building a simple, proven engine design to start, to understand the required tolerances and the level of effort you will be subjecting yourself to when you embark on building an engine of your own design. Lastly, if you haven't already noticed, model Diesels are rare, due to the added complexity they bring compared to a "normal" internal combustion engine. Higher forces, certain parts with extremely tight tolerances (fuel pump and injector) and a general lack of published working designs.

Lastly, I don't think you've shared much about yourself - your model engine goals or experience. It can help if I understand I'm talking to an experienced machinist or someone new to the hobby and machining...