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Best engine temperature for power/economy?

B

blue_tractor_man

Member
OK, here I go with another query. I was looking at the Nebraska Tractor Tests for the 8N (443) and the NAA (494). I was looking for differences in fuel economy and HP per pound of fuel, and HP per cubic inch between a flathead engine and the OHV. It seems that they are comperable.

But, I noticed that the NAA never got below 157 degrees, but the 8N was running at 130 degrees for part of the test. The air temperature was 74-75 for both tests.

Question one: how did the 8N get that cold? Would the thermostat not have held the temperature?

Question two: Is there an ideal temperature for an engine to get maximum power or fuel economy?

I read somewhere that Ford Motor Company raised engine temperatures to increase engine life, but they did not nention power or fuel economy.
 
Horse power tests are corrected for air temperature barometric pressure to standard atmosphere. Coolant temperature is up to the manufacturers.
 
(quoted from post at 21:20:29 12/01/18) OK, here I go with another query. I was looking at the Nebraska Tractor Tests for the 8N (443) and the NAA (494). I was looking for differences in fuel economy and HP per pound of fuel, and HP per cubic inch between a flathead engine and the OHV. It seems that they are comperable.

But, I noticed that the NAA never got below 157 degrees, but the 8N was running at 130 degrees for part of the test. The air temperature was 74-75 for both tests.

Question one: how did the 8N get that cold? Would the thermostat not have held the temperature?

Question two: Is there an ideal temperature for an engine to get maximum power or fuel economy?

I read somewhere that Ford Motor Company raised engine temperatures to increase engine life, but they did not nention power or fuel economy.
Click to expand...

Hot and a wee bit lean for efficiency. Moderate temperature and slightly rich for max power.
 
Complex question:complex answer. The hotter the engine runs, the higher the efficiency (pretty much all types of combustion engines) Efficiency leads to horsepower hours/ fuel. So for power per gallon, it is temperature. The hotter the combustion chamber, the less fuel is quenched at the colder walls and piston head. But if an assumption is made that the fuel detonates at a certain temperature, the surface temperature of the chamber is limited. Ceramic pistons and cylinders have been played with to stretch the envelope in this regard. The heat of combustion produces pressure that stays high if the engine surfaces do not cool it as it pushes the piston down. Or turbine around and around in a turbo (jet or gas turbine aircraft are in this category). Modern automobiles operate in the boiling range of pure water to raise fuel efficiency and emission reduction. Fuel air intake that is cool results in a denser charge, (more of it in the cylinder) Modern fuel injection atomizes the fuel far better than leaking it into a hot manifold (as with a carb) so cold air works to make a better charge. Intercooling supercharged air does this as well. The added density is worth the loss of Delta T in the chamber. Rumley, and other Distillate/Kero engines resorted to technical means to stay hot. Oil cooling, and shutters. Serious topic. Jim
 
I would agree with Jim, engine temperature hot as possible without autoignition, intake temperature as low as possible so you have dense air.

An engine with a carburetor is always going to be less efficient, as you need warm air to vaporize.

I am thinking that 200 degrees would be optimal.
 
Jim, ever hear of a man named Smokey Yunick?

He was an incredible engineer, inventor, innovator, race car driver, the list goes on...

He was known for being very innovative in his desire to win races. His motto was if the rules don't say you can't, then it must be legal. There were many rule changes written because of him!

Some of his later work as an engineer for GM was in the line of engine efficiency and emissions reduction without sacrificing performance. I think he was one of the engineers who worked on the V6 Buick turbo project.

But one area he worked on was developing engines that ran at extreme temperatures, ceramic pistons, high heat alloy cylinder liners and heads, GDI fuel system. He was also into tiny turbos, quick response, extreme RPM.

I don't think there was anything ever put into production, but some theories were proven that it could be done. Just a lot of practical problems were never worked out, like durability of adjoining components to withstand the heat.

Interesting concept though!
 
The 8N and older 9N and 2N ran acolde thermostat because the antifreez was plain achol and when the NAA came about thet had the permenant anti freeze that has a lot higher boiling point than the alchoal that if ran as hot as the NAA all the acholl would be gone before the day was out. How long would your beer set opened without being touched till it had all evaperated? Now set the perminet antifreeze out and it does not evaporate. Good reading on that is to read the Gus and the Model Garage stories avaible on line. Several of them involve the antifreeze boiling out.
 
I was going to mention Smokey, his biggest project that exactly pertained to this topic was his hot plasma intake Chrysler 2.2L turbo 4 cylinder engine he built & tested in the mid-1980's. Used exhaust gases to heat intake mixture to totally vaporize the gasoline/air intake mixture, exhaust driven turbo mostly stirred mixture to assure mixture had no rich or lean spots, little 4-cylinder ran like a Big Block, the little FWD car ran like a race car. Car was an '83 to '87 vintage Shelby Charger, used the Dodge Omni/Plymouth Horizon platform. Think it was Car and Driver magazine that had articles on that project. Much higher mpg, better performance, lower emissions, a Win-Win-Win.
 
The Rolls Royce Spey was(15,000 HP)operated at 1133 deg F / 612 deg C . This EGT would prove to be the optimum operating temperature so as all rotating foils / blades would be at min clearance between blades / foils tips and Honeycomb seals.

The General Electric J79/LM1500 operated under full load proved to be a true one of kind at 1000>1150 (EGT):

Both Units were installed on a natural gas pipeline. I was involved with the operational and maintenance program for just over 39 years.

Bob...Retired
cvphoto4456.jpg


cvphoto4457.jpg
 
My 2011 Silverado has an elaborate air intake system to ensure that it sucks in the coolest air available at the time/location/environment of it's operation. The cooling is controlled by 2 sequential electric fans that are operated and sequenced by the onboard computer. Once the engine comes up to temperature and remains running, the analog temp gauge on the dash sits at 210F and never moves.

It uses a conventional, push rod, 4.8 Liter V8, MPFI and performs tasks as good or better than my older 5+ liter V8 engines of the past on today's 87 octane fuel, at 50& or better economies.....exiting purer exhaust.

I compare that to my 1971 pig Chevy 4 door 400 cu in big block station wagon weighing a couple k# less running intake air right off the belt driven radiator/tranny cooler/AC cooling fan, gasping to get up to 10 mpg if it could ever get there running a 192 or thereabouts stat.

I know a lot has changed over the years in engine design, but with today's emission/efficiency rules, apparently hotter is better.......as are lubricants to tolerate such......my 2c.
 

The hotter you run an engine the more efficient it becomes.

You need a degree in physics to answer your question. Click below if you want to know how to calculate thermal efficiency.

About the best an internal engine can do is in the mid 30% efficiency.
Calculating thermal efficiency
 
In theory, a hotter engine is more efficient, because less heat is lost to cooling. But there are a lot of other factors, so the difference between running an engine at, say 150 degress vs 210 degrees is not that much. The temperature of the incoming air/fuel mixture has a more dramatic effect, since the cooler air is much more dense.

Over the 100+ year history of the gasoline internal combustion engine, the trend has been towards higher cooling system temperatures. This is for a number of reasons, not just efficiency. The hotter the coolant, the smaller the radiator needs to be. It's also easier to maintain a constant engine temperature with hotter coolant. But hotter coolant temperatures require higher system pressure and glycol coolant to avoid boilover, so it wasn't until the seventies when we had engines designed to run at over 200F.

Why did the 8N run so cold? Well, I suspect at least some of the coolant was bypassing the thermostat. I'm not familiar enough with the 8N to know why that would be, but looking at test 443 I see that when the water temp dropped below 150F, the tractor was running at low load (less than 10 hp) at about 2100 rpm. I'll also note that the specific fuel consumption went through the roof in these conditions, indicating the engine was probably being cooled by the evaporation of unburned fuel. (At full power, 26 hp, sfc was .56 lb/hp-hr. At 6 hp that went to 1.16, and at 2 hp sfc was a whopping 2.93 lb/hp-hr!)
 
(quoted from post at 02:17:04 12/02/18) The Rolls Royce Spey was(15,000 HP)operated at 1133 deg F / 612 deg C . This EGT would prove to be the optimum operating temperature so as all rotating foils / blades would be at min clearance between blades / foils tips and Honeycomb seals.

The General Electric J79/LM1500 operated under full load proved to be a true one of kind at 1000>1150 (EGT):

Both Units were installed on a natural gas pipeline. I was involved with the operational and maintenance program for just over 39 years.

Bob...Retired
Click to expand...

First run in 1954 with about 15,000lbs thrust. they put be getting scarce in applications today due to being worn out, relatively low fuel efficiency and obsolete parts .
 
(quoted from post at 09:11:33 12/02/18) In theory, a hotter engine is more efficient, because less heat is lost to cooling. But there are a lot of other factors, so the difference between running an engine at, say 150 degress vs 210 degrees is not that much. The temperature of the incoming air/fuel mixture has a more dramatic effect, since the cooler air is much more dense.

Over the 100+ year history of the gasoline internal combustion engine, the trend has been towards higher cooling system temperatures. This is for a number of reasons, not just efficiency. The hotter the coolant, the smaller the radiator needs to be. It's also easier to maintain a constant engine temperature with hotter coolant. But hotter coolant temperatures require higher system pressure and glycol coolant to avoid boilover, so it wasn't until the seventies when we had engines designed to run at over 200F.

Why did the 8N run so cold? Well, I suspect at least some of the coolant was bypassing the thermostat. I'm not familiar enough with the 8N to know why that would be, but looking at test 443 I see that when the water temp dropped below 150F, the tractor was running at low load (less than 10 hp) at about 2100 rpm. I'll also note that the specific fuel consumption went through the roof in these conditions, indicating the engine was probably being cooled by the evaporation of unburned fuel. (At full power, 26 hp, sfc was .56 lb/hp-hr. At 6 hp that went to 1.16, and at 2 hp sfc was a whopping 2.93 lb/hp-hr!)
Click to expand...

The cooler the intake air the greater the delta T and therefore delta P when heated by the same BTU's of combustion heat. Thus improved thermal efficiency.
 

There are still some people out there suffering the delusion that....If too hot is bad and boils over, therefore removing the thermostat and running coldest possible is better.
 
An overhead valve engine will produce more power and efficiency than a flat head engine. I replaced the flathead engine on my garden tractor with a over head valve engine and was shocked at the difference in economy. It uses about a third less gas to mow the same lawn! The smaller area of the combustion chamber walls is one reason. Any fuel molecules that touch the walls, either burn at much slower rate or maybe not at all. That's why engines with precombustion chambers haven't worked out. I had a Mazda diesel with precombustion chambers. It would never deliver the fuel mileage that it should have. Even the older large truck engines won't deliver the mileage that direct injection engines will.
 
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