Why an IC piston engine will Always beat out ANY external combustion system

After all of the thermal-chemical dynamics discussions it really just comes down to T-P&T.
Temperature Pressure generation versus Time available of harnessing these into mechanical energy.

In an IC piston engine only a small amount of fuel is used for the available atmospheric oxygen drawn into the cylinder. THEN that makes a temperature pressure rise within that cylinder. 2 cycle, 4 cycle or exotic 5&6 cycles NO Fuel is needed or used outside of this short time frame of TP burst.

An external combustion system of any type must make continuous Temperature and Pressure, always available regardless of the mechanical conversion harnessing system.
Consuming fuel all of the time. Maintaining the highest Temperature Pressure possible ALL of the time. With the resulting energy bleeding off, losses.

An IC engine can handily make a 400 to 850 psi and higher pressure rise power spikes. Can make a near instantaneous 450F to 1200F Temperature spikes too.

External combustion systems crap-out material-wise trying to do this continuously.

So chase mini-steam systems, Sirlings, Rankin-cycles, and such, all you want.
But on small personal use system IC pistons been kicking bun-bun’s dreamer-schemer ass’s for over a hundred years strong.

This same only-use-fuels just as needed, why the trend away from pilot light system to piezoelectric gas starting.
This same use-only-short released bursts of needed-energy, then coast along, why all refrigeration systems short cycle now.
Why fish, ocean mamalss, human bicyclist expend energy in pumped-bursts. Burst-pump, then glide. Repeat.

It is more energy use efficient.
Much much easier on the “equipment”. With much longer service lives.

Just how I see it.
Steve unruh


Theoretically speaking, Stirling engines are the best possible in terms of efficiency, but power to weight is extremely low, that is one of the reasons of not being used. Other reason is they are not readily availabe when needed. E.g. Steam engine… starting a steamer from cold is not exactly the same than starting a 2 stroke moped (just 1 kick and go…)

Some food for though: https://file.scirp.org/pdf/ENG_2015121717392471.pdf

PS: I’m biased, as my master thesis was the building of 3 Stirlings…


One pull in this winter weather on the B&S 10.5 hp wood splitter and it is up and running at 75% power.
Five minutes to fine spit a 5.2 cubic foot wheel barrow of 24 hour firewood. Engine and engine oil has become copletly heated up and all cold running crankcase cumbustion gasses engine sucked up. Burnt up and oil cleaned.
And I do this 250 days all heating system long.

No eternal combustion process system could do this.
Woodgasing for the engine fuel would add another five minutes to this use cycle.
Charcoal gasing for the engine fuel? Still . . . be a few minutes more.
The real energy losses then be in the reactor systems still hot cooling down with no fuel use needed.

True fuel cells, gas turbines, Wankels all have limited uses when space, weight, low viberation are the issues.
Otherwise give me a piston buzzer everytime; and I, Honda, Yamaha, Toyota, Kubota and Hyundai marine and all other dedicated IC piston engine manufacturers will kick anyone’s service-life/use-costs and fuel use ass’s.
Steve unruh


Yes its nice but has some issues.

Alloy Inconel is made mention of…
I worked for INCO…
Our new masters have done a good job of erasing the name from history


the turbine engine far surpasses any reciprocating engine any day as far as efficiency i have even seen them run on wood gas but for a car application they just dont work well as Chrysler found out =)


A stanley steam car of 1910 driven by my friend Guytou.


I do not agree with this statement.


ok so why dont we use this sys today oh ya they realized the turbo will run with out the piston engine…jet turbine

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Weight and complexity are the problem with turbo compound engines.
But just as piston powered aircraft have a lower fuel burn than turbo prop or jets the turbo compound principle is step ahead in efficiency over conventional diesel and gas engines.

And we do use this principle today you just need to know where to look.

In comparison gas turbo prime movers were never able to make the grade when it came to fuel burn in more than just the Chrysler turbine cars ( a fact for you the automotive technology the Chrysler corp developed from this was used by Chrysler defense and became the propulsion system of Abrams tank… A real gas guzzler, but light on its tracks )

Leyland is probably the best example of how to and why it won’t work.

The Canadian navy opted for gas turbines in the Tribal class destroyers.
Made them light and fast. but the fuel consumption meant they needed close support ships.
today its more common to see a diesel with a turbine to provide a burst of speed.

I think the US navy used some turbo compound Napier deltics in coastal patrol boats in the Vietnam era because of the light weight, high power and excellent fuel consumption.
But complex short service lives and very complicated engines.
I know the royal navy used them too as well as some locomotives.

Lots of very smart people here on this site.
You should take a step back and listen more closely to what people are sharing before you pass judgment.

Deltic, what a beutiful sound she makes!!!

The CN turb. pig on fuel to do what the deltic did.


Yes. Weight. Complexity. Dedicated maintenance requirements. Extreme precision manufacturing. Exotic expensive heat, pressure and erosion resistant materials need to get that so-called better efficiency.
OVERALL fuel use from cold ambient starting up to working power-use.
THEN energy/mass bleed off loses AFTER stop working use, shut down.

And two of these factors make it easy to see why no external combustion system can beat an IC piston engine system.

System material Mass-heat to power. The material mass’s needed to get to good fuels ionization for T-P power . . . then added to combustion areas mass; the material mass in “steam”, “expansion-gas” T-P power transfer to the mechanical power making parts of the system.
ALL external combustion systems simply require more system mass’s to get up to temperature; absorbing HEAT energy to make the Pressure, to make the pushing power.

New member Luis put up and excellent youtube video of a Brit who acquires an early 1960’s commercially made Stirling system small portable electrical power plant. LISTEN to the presenters words. Click enabled the cc option and read his words.
He did not even present from a cold starting up to power output portion because he said, “it would have taken too long”
He did say that the instruction manual stated to get the top hot end of the engine red glowing hot for full pressure and power capabilty. AND keep it that glowing hot c-o-n-t-i-n-i-o-u-s-l-y.
Old system. No service parts or support available and he chose to not run it full hot side temperature/pressure to not stress/wear/break it.
So for an only 400-600 watt electrical output system he showed only powering a single 100 watt incandescent light bulb.
Now same time era manufactured tiny-small Honda EM600. Same 600 watts rated output. One two pulls on the Honda flat head engine and up and running. Choke off and within less than 2 minutes getting the full 600 watts electrical output.
And yes. These were made in a kerosene fueled version for sale/use into India and Pakistan. Duel bowl carburetor. Started on the sub-gasoline side. Quickly switched to the kerosene side just as soon as the piston crown, valves and under cylinder head metal mass were warmed enough to support kerosene fuel-mist particles ionization combustion break down.
And now 50 years later that small Honda IC pistion system will give you either 4X the power for 4 hours: or a 10 hour 400 watt true standy-by power on just a single gallon US of gasoline.
Sirling performance is still stalled back as a fuel-use burner.

Only a complete fool runs his IC piston engine parts into red glow. Stupid. Sure failures making.
Hot rod/racing grand standing crap. Fine if the grandstand attendees are willing to pay for the show.
Ain’t no way to run a farm, trucking company, railroad, or commercial marine operation.
WHY: move around the world marine still use big massive IC PISTON engines.
Why: move millions of tons across continents Rail still use big IC PISTON diesel/electrics.

Oh folks do love to shout out steady-state numbers!
My dear older sister when she got her new-to-her 2007 Toyota Camry four cylinder loved to crow she was getting 40+ mpg. Sometimes her lie-o-meter would post hers as 44 mpg. Ha! A four cylinder Camry beating a same era Toyota Prius? No way sister dear. Now toggle-back my sister to a long-term lie-o-meter average . . . factoring in cold start warm-ups, and drive-always. Sitting at Tee intersection stop signs. Four and six-way traffic light intersections. Overall mileage of ~32 mpg. That ain’t bad. She is a feather footed driver. Unlike my darling wife racing up to stop signs. Groan. To save time. Burn more gasoline and brake linings, honey-bunny.

In IC piston engine only has to first ionize a small amount of air/fuel. THEN the small relative mass of the piston top upper cylinder wall, valve faces and under head combustion chamber heat quickly to full fuels ionization support, super quick.
You do not have to heat up the whole engine mass to get usable power.

External combustion you must heat up significantly all of the systems mass’s to get to usable power. Expended fuel energy for NO output power is always a loss!
What the super external combustion engine quacks always quick talk past hoping your will not notice.
Buy into their systems. Fuel operate their system, daily, year around, for real working AND YOU WILL NOTICE!
Only Gov’mints, University Geeks can afford to waste away moneys and efforts on steady-state lies.

Just his morning the loggers came to move their John Deere commercial log skidder to another site. Six cylinder inline Diesel. 27F this morning. It has sat unused for 4 weeks now. Glow plugged it to intake air heat for 15 seconds. Cranked to start in 30 seconds. White cold exhaust smoke for 2 minutes. Exhaust hot and clear then. It self powered itself up-ramp onto a high bed truck for road transport.
NO external combustion system historic, current, proposed, could have self-moved itself using that small amount of fuel.
Best case maybe external combustion 30 minutes to warmed up to enough power to pull itself out of it’s own shadow. CONSUMING fuels that whole warming up to usable working power time!

Too long? Too hard to follow?
An IC piston engine heats up to working from the inside core, to the outside.
Any external combustion engine system must heat up to working from the whole outside to the inside core.

Just the the Real-of-it, man.

Steve unruh


Horses and ox are also internal combustion.



The linear Stirling Sunpower developed to be used in a wood stove was rated at 1kw. The linear design has quite good efficiency reliability and mechanical simplicity. Gas bearings, no contact movement. A half a century, and a leap in technology from the WWII Philips generator.

I think there are different ways to look at system effectiveness. If ample energy is available, then energy efficiency is second place. If energy is more costly or scarce then it’s more important. Also, adoption and diffusion of technology bears on practicality.

The fact that linear Stirlings are used on solar concentrators (instead of steam engines / turbines etc) is the last word on efficiency and reliability, cost effectiveness.

No, they can’t match start up time with IC, just as IC can’t match the torque of a steam engine. Apples and oranges.

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lol there actually “electro-chemicle” like all animals lol

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Yes, it’s true Internal Combustion Engines (ICEs) rule the day, for small applications. But remember that coal fired electric generating plants mostly use steam turbines. Why? because roughly 60% conversion efficiency. And remeber the Besler brothers fitted a Doble steam boiler and engine to an aeroplane with impressive results. Then Commander Lamont came along and made a boiler with an even bettter power to weight ratio. The darn thing could even use sea water and not scale. I think there is still a lot of development work that could be done with steam.



Economies of scale.


Go ahead. Love your Stirling dreams. Love your micro-(modern)steam.
How do they actually work? DeltaT differences between the Hot side/end, versus the Cold side/end.
You must maximize this temperature difference to produce the Pressure that will make the shaft power.
And that means the Hot end must be in glowing metals levels of heated, continuously.
Steam combustion areas are well know for severe metals degradation and erosion’s. A known continuous maintenance restore requirement.
Stirling the same/same kill the hot end thermal problem.
Ahh . . . cool better the cold end, eh?
New member Luis also put up excellent info on the modern Swedish diesel/electric/Stirling cycle submarines. Great. Quiet. Much cheaper than a Nuclear/steam system.
Great in cold northern seas and oceans for cold-end making.
Noted was the need to system modify when deployed experimentally by the US navy into warmer Mid and South Pacific waters.
And I’ll wager a great part of the system modification when in warm Cold-side waters was simply accepting much less performance.

IF these alternative systems were Real-World deployable and useable you can be damn sure that Honda, Toyota Yamaha, Kubota, Hyundai would on their own development dollars be manufacturing them commercially and selling them.
You really think if the Russian or mainland Chinese governments had a better heat-engine-tech that they would not be using them and supplying to client states? They would.
They work on IC piston engines with improved stretched out power wring cycles like Atkinson, Miller, GDI, coolant heat recovery vacuum bottles, etc.

Belief in hidden patents, suppressed power technology, undiscovered world-revolutionary energy “laws” is the same as actually believing in the Tooth Fairy. Only mamma, dada, put those coins under the pillow because they love you.
Bogus. Fantasy.

IC piston engines have hard work earned their place.
The trick of it is actually matching the engine configuration to the Whole-equipment usage for maximum benefits.
What you say?
In the USofA for a time period there devolved a broad difference between motor gasoline’s and diesel fuel retail prices. A minimum 25% to up to 50% at times.
Only a very few Mercedes and Peugeot diesel cars existed.
Many here for a time put small 4 and 6 cylinder diesel into full sized American sedans and vans. Water cooled Perkins, Nissan, Detroit’s were all done. Not easy. But with good fuel-costs savings results.
A very few actually installed aircooled German Duetz diesel engines. O.K. for motive power. But the shit’s for cabin and windshields heating! Ha! Fast forward to the cold climate plug-in electric vehicles power-for-heat problems. The ONLY aircooled VW I ever rode in with great in cabin heat was a micro-bus camper with an axuillary gas space heater.
The auto manufactures rushed factory diesel cars and small pick up out to be available. Of course the combo of refiners rejiggering output for higher profit gasoline’s, and revised federal and State road fuel taxes had wiped out the gasoline versus diesel retail disparity.
NOW road-use pump diesels is taxed higher to reflect it’s higher energy content. And now higher evil “carbons” content.
Why the Asian ans American manufacturers are still very lukewarm on advanced car diesels. It’s a German-thing. Because of in-country fuel taxation biasing the results.

Point. Stop fixating on steady-state “lab” idealization in isolation for ALL of the overall use-needs.
Fuel-use results is always important. There IS no cheap, free heat energy. It all costs.

Steve unruh


Good read Mr Wallace.
30 bar capable. That far past what an only single-edge wiper sealed Wankel could ever achieve. Wankels. Another pie-in-the-sky fuel-use hog that never should have had 100’s millions dumped into it.
I worked on a few Wankels. For pay. Never dumb enough to buy into one.

I’ve had IC piston engines with 2-3-4-5-6 sealing ring assemblies. The designer can choose just want will be needed. The designer can match the power-expansion ratio and expansion rate of change to tailor to any-all fuels compressed burn rates, and loaded conditions.

External combustion. Nope. And Nope.



I have a gas powered wood spliter , I do not want steam powered wood spliter .
I also splt wood with an ax . some logs realy need 32 tons to reduce them , no way to split them just mash them a bit .
I found one aplication where I think a turbine is better then an Internal combustion engine .
but an internal combustion engine would never be considered for this application .
The Organic Rankine Cycle’s principle is based on a turbogenerator working as a conventional steam turbine to transform thermal energy into mechanical energy and finally into electric energy through an electrical generator. Instead of generating steam from water, the ORC system vaporizes an organic fluid, characterized by a molecular mass higher than that of water, which leads to a slower rotation of the turbine, lower pressures and no erosion of the metal parts and blades.
Turboden supplies a 8 MWe ORC unit, Turboden 80 HRS. The application of the project consists in biomass power plant employing wood waste from the adjacent wood pellet manufacturer, Maine Woods Pellet Company, LLC. SolaGen and NEC supply the engineering and manufacturing of the biomass fired Thermal Oil Heater and Waste Heat Pre-dryer plant to be integrated with the existing pellet plant. Mid-South Engineering Co. take care of the BoP (Balance of Plant) and the system integration of the project. The competitor was the traditional steam technology. Customer has been convinced by the advantages of Turboden ORC technology (mainly minor O&M Operating and Maintenance Costs in comparison to traditional steam technology).


you missing one glaring fail with steam…its “external combustion” not “internal combustion” but gas turbines “jets” are more efficient than a reciprocating piston engine =)

I am going to debunk this with some numbers from some aircraft engines.
One of the very best piston engines for fuel consumption of its type the diesel Jumo 205 ( of the 1930s ) has a burns rate of 213 g per kWh at its most efficient speed.
One of the very best turbo props the Pratt&Whitney PT6 consumes 308 g per kWh.

In descending order you have turbo fans, axial compressor turbo jets and centrifugal jets ( Helicopter )

Now if you really want to see fuel turned into smoke, hit the reheat like the Concord.

If you really want to save fuel and be as simple as possible Uniflo turbo diesel the FM OP series are some of the best.