Experimental with a diesel engine

[RFguy]

some useful reading :. interesting real time, closed look hydraulic  clutch  control to adaptively deal with the pulses and resonances

https://www.diva-portal.org/smash/get/diva2:846145/FULLTEXT01.pdf

 

Edited September 17, 2022 by RFguy

[onetrack]

A fluid coupling would be an excellent way of absorbing power pulses and even providing a method of vibration damping.

Porsche actually lodged a patent for a fluid coupling for the thrust propellor on a gyroplane, but appears to have let the idea lapse. Maybe weight was the bugbear.

 

https://patents.google.com/patent/US4970860A/en

[RFguy]

Hi OneTrack-

yeah- hence my question about a torque converter in its simplist form.  Efficiency may be an issue. Modern TCs as you know are lock-up style for 'cruise'.

 

I'm guessing the combo of the gear box cut and some slip  and the overload clutch provides the reduction of the power pulses for a 4 cylinder rotax.  4 cylinder engines are troublesome.

 

Of course we all want a 60deg V12.

see plots in this link

http://www.epi-eng.com/piston_engine_technology/torsional_excitation_from_piston_engines.htm

 

 

One of the prop mfrs writes that its not so much the pulses at WOT that cause a problem, its WOT pulses at low prop load - IE prop at low RPM, unloaded, not much to do and operator applies WOT...... In those cases prop is unloaded and cant soak up the pulse and also is underdamped without high load  and can resonate ...

 

 

 

 

 

 

 

[Thruster88]

For anyone lusting after a turbo diesel kit plane engine the Mitsubishi Triton  engine, 4N15, in service since 2015 would be a good choice. All aluminium block and head. 430nm@2500rpm = 150hp. 2500 is perfect propeller speed. It weighs 163kg so maybe 185kg installed with cooling.

 

For comparison the most bullet proof aircraft piston engine on the planet (lyc o-320) weighs 121kg and also produces 150hp@2500rpm.

Edited September 17, 2022 by Thruster88

[turboplanner]

45 minutes ago, Thruster88 said:

For anyone lusting after a turbo diesel kit plane engine the Mitsubishi Triton  engine, 4N15, in service since 2015 would be a good choice. All aluminium block and head. 430nm@2500rpm = 150hp. 2500 is perfect propeller speed. It weighs 163kg so maybe 185kg installed with cooling.

 

For comparison the most bullet proof aircraft piston engine on the planet (lyc o-320) weighs 121kg and also produces 150hp@2500rpm.

Given the weight difference and the need to fit a radiator and cooling system to the Mitsubishi, I wonder why people would be looking at diesel?

[Bosi72]

8 minutes ago, turboplanner said:

Given the weight difference and the need to fit a radiator and cooling system to the Mitsubishi, I wonder why people would be looking at diesel?

$$$

[skippydiesel]

Ref. Direct prop coupling 

 

Cant see it it - Rotax have proven (at least to me) that in relativity low hp  (sub 200hp) engines, the way to go is liquid cooled, high engine speed, through a reduction system to optimum prop speed . Why? cause the efficiencies conferred by this concept  are  improved combustion (lower fuel consumption/greater power:weight), lower vibration  & noise and in the case of Rotax reliability.

 

Ref. Comparing very large diesel performance with small light weight aircraft engines.

 

Cant see this either. Large slow revving diesel are incredibly heavy (power:weight) to cope with the combustion process - if diesel aircraft engines are ever to be a modern reality, they must (again in my view) go the Rotax route eg Austro  & Fly Eco (both MB engines). 

 

[turboplanner]

1 hour ago, skippydiesel said:

Ref. Direct prop coupling 

 

Cant see it it - Rotax have proven (at least to me) that in relativity low hp  (sub 200hp) engines, the way to go is liquid cooled, high engine speed, through a reduction system to optimum prop speed . Why? cause the efficiencies conferred by this concept  are  improved combustion (lower fuel consumption/greater power:weight), lower vibration  & noise and in the case of Rotax reliability.

 

Ref. Comparing very large diesel performance with small light weight aircraft engines.

 

Cant see this either. Large slow revving diesel are incredibly heavy (power:weight) to cope with the combustion process - if diesel aircraft engines are ever to be a modern reality, they must (again in my view) go the Rotax route eg Austro  & Fly Eco (both MB engines). 

 

A 600 hp truck engine weighs a tonne, its cooling and mounting system weighs about the same as an ultralight.

An engine for a 4WB, like the Triton is designed for very hard use.

So I suggest no one would simply go down that route or slavinshly copy the principles of existing petrol engines.

 

They would design an engine for an aircraft.

When you start from a blank sheet of paper as most designers do, you decide the cooling system, and after the intensity of design in WW2, if it's a piston engine you would probably go air cooled.

 

 

 

 

[skippydiesel]

3 hours ago, Bosi72 said:

$$$

Not just dollars - a ground based engine of 1.3L must have a relative (to aircraft) large radiator to accommodation slow/stationary operation and a high degree of blockage (insects/chaff/dust/etc).

Up until recently, ground engines did not routinely run an engine oil cooler - so were further dependent on the radiator for cooling (& a large sump capacity).

The aircraft engine most similar to ground engines, Rotax, used a little over 3 litres of engine oil, with a slightly larger liquid capacity cooling system. This is much smaller than what would be routinely found in your average 1.3L car.

A diesel engine of similar output (say 90 hp continuous ) would probably require slightly larger oil/coolant capacity. I would expect the higher torque to facilitate courser prop settings which may offset a potentially poorer take off & climb performance and also give superlative econamy at cruise.

[skippydiesel]

1 hour ago, turboplanner said:

A 600 hp truck engine weighs a tonne, its cooling and mounting system weighs about the same as an ultralight.

What?? are you positive about this? Even my 3.2L Rangers radiator is much much  larger than my Rotax

1 hour ago, turboplanner said:

......................and after the intensity of design in WW2, if it's a piston engine you would probably go air cooled.

So not an admirer of the Rotax line of 4 cylinder semi liquid cooled engines.

1 hour ago, turboplanner said:

 

 

 

 

 

[danny_galaga]

Yuck, I hate diesel particulates. You wanna add MORE to the mix 😄

[turboplanner]

49 minutes ago, danny_galaga said:

Yuck, I hate diesel particulates. You wanna add MORE to the mix 😄

Let me know when you find one behind a new truck; they drive through the suburbs sucking in particulates, coook them and pretty blow out close to zero particulates; certainly they leave behind less particultates that were there.

 

I've recommended "Revving Parties where everyone brings their new trucks into the cities and revs them for an hour or so once a week.

[turboplanner]

2 hours ago, skippydiesel said:

So not an admirer of the Rotax line of 4 cylinder semi liquid cooled engines.

 

Not against them, but if you don't have hoses you don't have hose failures.

[danny_galaga]

7 hours ago, turboplanner said:

Let me know when you find one behind a new truck; they drive through the suburbs sucking in particulates, coook them and pretty blow out close to zero particulates; certainly they leave behind less particultates that were there.

 

I've recommended "Revving Parties where everyone brings their new trucks into the cities and revs them for an hour or so once a week.

How about all those bozos that disable all that new fangled crap on their land cruisers and land Rovers just so they can blow HEAPS of smoke? Because, you know, it's more manly. Let's see them laugh it up when their kid gets asthma , tools...

[skippydiesel]

17 hours ago, turboplanner said:

Not against them, but if you don't have hoses you don't have hose failures.

I am sure there must have been at least one hose failure but for the life of me I have no knowledge of such an event.

In the real world adhering to Rotax recommended service intervals/materials would seem to reduce such concerns to the realm of theory.

[turboplanner]

8 minutes ago, skippydiesel said:

I am sure there must have been at least one hose failure but for the life of me I have no knowledge of such an event.

In the real world adhering to Rotax recommended service intervals/materials would seem to reduce such concerns to the realm of theory.

In the real world many people don't adhere to manufacturers recommendations.

I know one guy who wrecked a perfectly good aircraft because he bought hoses from a discount car parts shop.

What you could do in designing an engine if you thought everyone would be compliant and what you need to do in the real world are two different things.

 

[RFguy]

I think the rotax water system is OK, for the flexibility in hot conditions that we get.  It's pretty foolproof if you pay attention to maintenance, leaks etc.

just PITA hose sizes (17mm hose !) FFS Rotax. anyway, silicone 5/8" works OK. 

 

[skippydiesel]

3 hours ago, turboplanner said:

In the real world many people don't adhere to manufacturers recommendations.

I know one guy who wrecked a perfectly good aircraft because he bought hoses from a discount car parts shop.

What you could do in designing an engine if you thought everyone would be compliant and what you need to do in the real world are two different things.

 

Is this not Darwinian selection in action?   

[Ian]

On 16/09/2022 at 12:39 PM, Yenn said:

What is meant by you can't design an Otto engine without an ignition system, or maybe I should ask. What is an ignition system?

The Otto cycle includes both normal petrol and diesel systems, Diesels don't have an electrical system for ignition. They compress the charge so that it's temperature becomes hot enough to ignite the diesel, when it is injected.

Hi Yenn, think about it, there's a difference between the Otto and Diesel cycle, that's why they each have a name. Notice the differing shapes of the Pressure/Volume diagrams for ideal cycles describing both. The otto cycle requires an external source of ignition because the temperature rise due to compression becomes less when you throttle. A diesel always compressess a constant volume so the pressure rise is constant regardless of throttling.

Rather than explain it read the below.

https://en.wikipedia.org/wiki/Otto_cycle

https://en.wikipedia.org/wiki/Diesel_cycle

And here's an explanation of the difference from where I stole the diagrams. https://mechcontent.com/otto-cycle-vs-diesel-cycle/

Of interest is that the Otto cycle is more efficient than the diesel for a given compression ratio. The diesel cycle is practically more efficient because the higher compression enables a higher combustion temperature, laws of thermodynamics etc. From the wikipedia article.

Quote

Comparing efficiency to Otto cycle

Comparing the two formulae it can be seen that for a given compression ratio (r), the ideal Otto cycle will be more efficient. However, a real diesel engine will be more efficient overall since it will have the ability to operate at higher compression ratios. If a petrol engine were to have the same compression ratio, then knocking (self-ignition) would occur and this would severely reduce the efficiency, whereas in a diesel engine, the self ignition is the desired behavior. Additionally, both of these cycles are only idealizations, and the actual behavior does not divide as clearly or sharply. Furthermore, the ideal Otto cycle formula stated above does not include throttling losses, which do not apply to diesel engines.

 

[Geoff_H]

I like the dual cycle engines that are becoming popular in modern vehicles.  The combustion starts as an Otto then converts to a diesel cycle (using petrol).  These engines are more efficient than both diesel and Otto.  When you see the temperature entropy and pressure enthalpy graphs this is shown.  The best reason that I like them is that Mercedes is getting 400hp out of a 2 litre engine.  I feel that a small engine with that output and efficiency could be the future for aircraft.  My vehicle has a 2 litre 250hp engine and gets 6.4 litre/100km, very reliably, it has a dual cycle engine. It's manufacturer was talking about dropping the less efficient diesel engine in its favour.  All seems to have changed now that the "climate change religion" reigns suprime.

[skippydiesel]

It seems to me that all  piston engines will require a certain level of "robustness" for a given power output. Robustness almost always means weight - the higher the power output the greater the weight. This may not be much of a considerations for land based vehicles but for aircraft presents as a major hurdle.

 

Is this not the main reason why diesel engines with their "attractive"  characteristics (power/econamy/high flash point fuel) do not seem to quite "make the cut" as propulsion units for aircraft?

 

I would like to hear /know more about Geoff_H's Mercedes engines, as they may offer at least part of a solution however I suspect higher weights than a conventional petrol  & lower weights than a conventional diesel (good compromise?).  The "management" required for greater combustion complexity may lead to reliability issues - please expand . 

[turboplanner]

54 minutes ago, Geoff_H said:

I like the dual cycle engines that are becoming popular in modern vehicles.  The combustion starts as an Otto then converts to a diesel cycle (using petrol).  These engines are more efficient than both diesel and Otto.  When you see the temperature entropy and pressure enthalpy graphs this is shown.  The best reason that I like them is that Mercedes is getting 400hp out of a 2 litre engine.  I feel that a small engine with that output and efficiency could be the future for aircraft.  My vehicle has a 2 litre 250hp engine and gets 6.4 litre/100km, very reliably, it has a dual cycle engine. It's manufacturer was talking about dropping the less efficient diesel engine in its favour.  All seems to have changed now that the "climate change religion" reigns suprime.

That's been the trend I'm seeing also.

The tightening of emission laws on Particulates and Nox have driven the engine manufacturers down this path with the byproduct of using a fraction of the fuel per kilometre compared with past decades.

It's now possible to mount a case that today's vehicles clean up the static-based emissions in cities.

The engines are also lighter and often outlast the vehicle before needing an overhaul, a huge advantage in commercial vehicles where the total daily operating costs are shot to pieces if an overhaul is required.

 

[onetrack]

One must keep in mind that diesel as a fuel has a much greater energy content than any variety of petrol, litre for litre. Load a petrol engine up, and the fuel economy goes to hell in a handbasket - but load a diesel engine up, and its performance far outshines any petrol engine.

There's a reason why we never see petrol-engined trucks today, and why light-weight, high-speed diesels have become so popular in vehicles where regular trailer/van towing is a big part of the vehicles use.

In addition, a diesel engine is more efficient at extracting the energy from the fuel, than any petrol engine. The newer high-tech petrol dual cycle engines are reliant on a great deal of electronics to keep them operating efficiently - and even then, they are still behind diesels in total economy.

 

https://www.acea.auto/fact/differences-between-diesel-and-petrol/

[facthunter]

The area of the combustion chamber is important to efficiency. More area more heat loss. This is the reason the sidevalve engine will never get the efficiency of an OHV type.  Nev

[RFguy]

not sure about diesel havign a higher caloric value.... diesel economy comes from thermal efficiency.

Diesel does have a  higher  CG so more MJ/litre

 

gasoline MJ/kg : 44-48    and 32 to 36 MJ/m3

diesel  44-48    and 36 to 40 MJ/m3

kerosine. about the same

Hydrogen : 120 MJ/kg  but only 12 MJ/m2