increase engine heat for better efficiency?

From Easy Rider,

"I suspect that running really hotter like 230 degrees F would allow you to lean out the mixture for some REAL economy. Unless you can lean out the mixture the increase in efficiency will be fly stuff. A gas engine needs a rich mixture to run fairly well when cold and can lean out when warmed up. Could one lean considerably more if the coolant temperature was raised considerably higher than normal?" Perhaps 250 to 300 degrees is possible with a very high pressure cooling system. But could one continue to lean the mixture? And by how much? And would it deliver much greater efficiency?


ANS: Yes, within limits you can ignite the fuel/air mixture with a leaner mixture in a higher temperature combustion chamber. However leaning the mixture beyond what is now normal practice will not bring better efficiency (conversion of fuel energy to output power). Modern well tuned engines run somewhat leaner than the ideal for efficiency, because the leaner burn produces less emissions.

In basic thermodynamics, the internal combustion engine cycles all have better efficiency with higher combustion temperatures, and the maximum temperatures are obtained with a slightly lean mixture. Further leaning of the mixture begins to lower the combustion temperature, so the engine efficiency begins to get lower. Maximum combustion temperature tends to produce Nitrous Oxide (NOx) emissions (plus a few other undesirable emissions), so the EPA rules require engines to be designed such that these conditions are minimized.

Running engines with temperatures far beyond 250F-300F can, and is, done with many air-cooled engines.

 

From Powerabout:

"so do SI engines with non roller cams
put a cam and lifters in an old engine and you have to run it in with Shell Rotella"

I do not understand your question, are you asking if Shell Rotella (a Diesel engine CI oil) would be required for SI engines that do not have roller cam followers?

As stated in the previous post, the SI oils and the CI oils all work very well for all normal conditions of use. In heavy load conditions the CI oils tend to prevent failure and wear better than the SI 5-30 oil, but that does not mean that the CI oils are mandatory for an engine that does not have roller cam followers.

 

Seeing as "lean" is mentioned,gas engines are the topic and from my experience and common knowledge: lean + hot = burnt valves.

 

Fredrosse
Unless I am mistaken here, you are saying that you can and perhaps should use a Diesel, C rated (which stands for Commerical) oil in a gas engine due to heavy loading. There are additives within the C class oils that are not good in a gas engine but vital for a diesel. Mainly detergents.

You say that a 15w-40 C grade diesel oil would be better than an S grade 5W-30

I doubt any marine engine manufacturer would specify a 5W oil as this is the Winter designation, and this oil is rated for an ambient starting temperature of -20 degrees F

At the running temperatures, a 40 oil could support more load than a 30 oil if the engine could actually break down the oil film of the 30. So to be realistic, a 20W50 in an oil designed for a GAS engine, without the Diesel additives which can be harmful to a gas engine, would be a better choice. So a 20w-50 S (Service designation for gas) would be a better choice than a 15w40 C (commercial designation for diesel) oil.

A 20W oil is recommended for a starting ambient temperature of 20 degrees Fahrenheit and water is pretty solid at that temp, it is unlikely that many marine engines will be started at that temp

 

The "C" rating stands for "Compression Ignition" type engines, the "S" Rating stands for "Spark Ignition", and both types are high detergent oils.

Barry stated: "So to be realistic, a 20W50 in an oil designed for a GAS engine, without the Diesel additives which can be harmful to a gas engine, would be a better choice." Actually the anti-wear and anti-scuffing additives in the "C" rated oils are NOT bad for a GAS engine, but can be bad for a catalytic converter, and for the environment if not disposed of properly. The wearing parts, whether Diesel or a SI engine, hold up better with these additives.

I am not saying one type is "better", but merely that the S rated oils presently promoted by the industry will give some better economy, I think in automobiles the average is a few gallons of gasoline saved every year, doesn't sound like much, but with a hundred million automobiles in the USA, it adds up to considerable amounts of fuel saving.

The higher viscosity "C" rated oils sacrifice a fraction of a percent in fuel economy, but result in less wear within the machine. The "C" rated oils also have some undesirable anti-wear additives (from an EPA standpoint), but it appears that heavy duty Diesel engines do not hold up well enough without these additives, so they are allowed for Diesel rated ("C" rated) oils.

Which oil you should use depends on where you place value, if the fraction of a percent fuel consumption is more important than engine wear, then use "S" rated oil. If you are concerned about potentially reducing the efficiency of the catalytic converter (if you have one) in your spark ignition engine, then use the "S" rated oil.

If you want maximum engine life, then choose the "C" rated oil. In my automobiles I always use "C" rated oils, independent of whether the car is Gasoline or Diesel, but then I always keep the car to about 250,000 miles, and do not want to ever rebuild the engines. In my boat engines I have never had enough run time to wear out an engine, but I still use "C" rated oils, considered as some extra insurance against failures.

 

Good morning Fredrosse
The American Petroleum Institute, API, the organization which sets the standards for the designation for the Donut or Star mark on a can of oil in the USA and which Canada adopts disagrees with you.

Specifically in their explanation of the interpretation of the mark, they explain that the S stands for Service, gasoline engines and C stands for Commerical, diesel

The first letter of the Gasoline engine is S ( for service) and the second letter is a category which started ages ago as SA, SB, SC and so on up to SH. These oil designations are now obsolete and replaced by SJ, SL SM

For Diesel the designation is C (for Commercial), same scenario CA up to CJ of which some of these are obsolete.

My concern is that you are recommending "if you want maximum engine life, then choose the "C" rated oil", when in fact it the diesel specific additives may be detrimental to a gasoline engines health

I believe somewhere in this thread a contributor mentioned that the loading on the crank bearings are higher in a diesel due to the higher compression ratio. While this is true, a higher compression ratio obviously means more load on the con rod, keep in mind that only about 15-20% of the load in an engine is due to the compression load and the load imposed from the fuel firing on ignition. The majority of the load on the con rod is due to the forces developed by acceleration of the piston mass moving up and down the cylinder.
Additionally, Fred, check out the web information on LTC which stands for Low Temperature Compression. You said that it is better to have a high combustion temperature for better efficiency, I disagree and evidently so do the engineers. Additionally, for diesels, the lower combustion temperature lowers emissions

 

From Barry: "The American Petroleum Institute, API, the organization which sets the standards for the designation for the Donut or Star mark on a can of oil in the USA and which Canada adopts disagrees with you.

Specifically in their explanation of the interpretation of the mark, they explain that the S stands for Service, gasoline engines and C stands for Commerical, diesel." ....... "For Diesel the designation is C (for Commercial), same scenario CA up to CJ of which some of these are obsolete."

I see no disagreement here, I guess they added the terms "service" and "Commercial" to the descriptions, so that lay people would not get confused, however the ratings still mean the same thing:

S rating is for spark ignition gasoline type engines.

C rating is for compression ignition Diesel type engines.

 

From Barry: "My concern is that you are recommending ... the "C" rated oil for maximum engine life, when in fact it the diesel specific additives may be detrimental to a gasoline engines health."

I understand your concern, and ask if you have any technical basis for the statement.

From a technical standpoint, two oil properties relate to less wear. One is viscosity, higher viscosity means less wear, any real engineer can vouch for this. The second is the anti-wear additives, and I know very well the fight that went on with the environmentalists when the EPA was going to ban the anti-wear additives, and the trucking industry lobbied to allow these additives for Diesel engine oils. I am no expert for all the properties of these additives, but I believe they do indeed reduce wear, and the trucking industry lobbied because they are proven effective. I cannot see where the protection these anti-wear additives give Diesel engines would not be applicable to gasoline engines, Basically the same type of wearing surfaces, iron and steel sliding on similar materials.

 

From Barry: "I believe somewhere in this thread a contributor mentioned that the loading on the crank bearings are higher in a diesel due to the higher compression ratio. While this is true, a higher compression ratio obviously means more load on the con rod, keep in mind that only about 15-20% of the load in an engine is due to the compression load and the load imposed from the fuel firing on ignition. The majority of the load on the con rod is due to the forces developed by acceleration of the piston mass moving up and down the cylinder. "

This surprises me that the inertial bearing loads are 500% - 700% of the power stroke piston pressure loads. It is a simple matter to determine these dynamic loads, and determine where this type of load combination is common. More after I weigh some pistons and rods.......

Went into the shop and found the Yanmar Diesel piston and rod that I had replaced years ago. A Yanmar TS-60 engine, 75mm bore & stroke, the piston weighs 0.79 pounds, the connecting rod 0.45 pounds. This engine is rated at 5 HP/1800 RPM. Doing the math, the peak centrifugal force on the piston is 109 pounds (on the wrist pin), and 183 pounds force on the big end bearing.
This engine has a BMEP (Brake Mean Effective Pressure) of 120 PSI, giving a MEAN piston power stroke pressure force of 820 pounds. So for this actual Diesel, the acceleration forces are only about 15% to 20% of the BMEP pressure force. The peak pressures in the cylinder are several times the BMEP value, so at least this engine has only minor inertial loads compared to the piston pressure loads. I know this is a conservatively designed Diesel, which ones have the inertial loads many times the pressure force loads?

 

Barry stated; "You said that it is better to have a high combustion temperature for better efficiency, I disagree and evidently so do the engineers. Additionally, for diesels, the lower combustion temperature lowers emissions"

In today's world of pollution concerns, the suppression of combustion temperature can reduce emissions, while still using the Diesel cycle with its inherent higher efficiency than available with gasoline engines. The articles I see about LTC (Low Temp Combustion) engines refer to getting emissions down, while still maintaining good Diesel efficiency. The statements that efficiency is improved refer to the switch from gasoline engines to Diesel, not to LTC providing better efficiency than high temperature combustion in a Diesel engine.

Higher temperature combustion in virtually all air standard internal combustion power cycles indicates higher cycle efficiency, this is fundamental to all of these cycles, Diesel, Gasoline, Gas turbines, etc. Any real engineer will confirm this fact.

Design of real engine cycles involves compromise, to get several factors into an acceptable regime, and to get the machine to hold up satisfactorily, and to meet emissions, and to meet noise limits, etc. The promoters of new technology often "guild the Lilly" with maximum hype to get their products, or their research grants, ahead of the competition.

 

Fredrosse says
Higher temperature combustion in virtually all air standard internal combustion power cycles indicates higher cycle efficiency, this is fundamental to all of these cycles, Diesel, Gasoline, Gas turbines, etc. Any real engineer will confirm this fact.

The following are some papers done by REAL engineers that prove with research that a cooler combustion temperature produces a higher efficient engine. These are not companies trying to sell new research but one of them is a paper presented by engineers to the SAE Society of Automotive Engineers symposium . Additionally, there are several papers written by engineers discussing a lower combustion temperature increases efficiency of turbines etc.
The concept is simple, the higher combustion temperatures create more heat which is not converted to mechanical energy. If you can lower the temperature, less energy is lost as heat and more is usable for mechanical energy, ie less fuel in , more mechanical energy out, = higher efficiency

www.sae.org/events/gim/presentations/2013/foster_dave.pdf‎

www.vecom.org/members/documents/.../VECOMBohacweb.pdf‎


Fredrosse states
From a technical standpoint, two oil properties relate to less wear. One is viscosity, higher viscosity means less wear, any real engineer can vouch for this. The second is the anti-wear additives, and I know very well the fight that went on with the environmentalists when the EPA was going to ban the anti-wear additives, and the trucking industry lobbied to allow these additives for Diesel engine oils. I am no expert for all the properties of these additives, but I believe they do indeed reduce wear, and the trucking industry lobbied because they are proven effective. I cannot see where the protection these anti-wear additives give Diesel engines would not be applicable to gasoline engines, Basically the same type of wearing surfaces, iron and steel sliding on similar materials.

My response
There are also wear additives in S class oils. In C class oils, there are dispersion additives, detergents which can be harmful to a S engine. Castrol in one of their papers specifically say not to use a C class oil in S type engine

I will get back to you on the loading due to the acceleration load placed on bearings due vs combustion loads. Interesting that you have a Yanmar as I understand that they were one of the first if not the first to create high rpm diesels with low reciprocating masses. The lower masses lowers the forces caused by acceleration of the piston. In one of our Mech Eng labs, many many years ago we had to do the calculations and stress analysis on the connecting rods, and the conclusion was that I had stated, 80% of the load in the connecting rod comes from the acceleration
Cheers

 

My computer could not get to the links you posted?

"Wear additives in S class oils"; Yes, I would expect that is so, but I would also expect the additives in the C rated oils would be more "heavy duty".

"C oil dispersion additives, detergents which can be harmful to a S engine": I have never seen any evidence to that point, but would like to know more

"Castrol in one of their papers specifically say not to use a C class oil in S type engine": Yes, I would expect that, the industry consensus is to use S oils in spark ignition engines, and C oil in compression ignition Diesel engines. The point I am making is that the C rated oils prevent wear better than the S rated oils. There are many other factors that Castrol, or Mobil, or Shell need to consider, especially emissions, environmental concerns, fuel consumption, and marketing issues.

Any further details here would probably not add anything useful on this forum topic, and it feels like it has almost become like a "Hissing contest". I guess we will have to agree to disagree.

I would however like to see any data you may dig up on the dynamic loading issue, since my calculations for a real, and once very popular engine show something quite opposite what was stated.

 

"Castrol in one of their papers specifically say not to use a C class oil in S type engine":

Probably a marketing scare against Rotella T , used in all engines

 

Rotella T goes into every engine I have, excepting the external combustion engines.

 

"it feels like it has almost become like a "Hissing contest". I guess we will have to agree to disagree. " Fred, it is not my intent to create a hissing contest but to question your statement that C rated oils when used in a gas engine will reduce wear. Lost perhaps to many viewers if they take your advice and put it in an automotive engine is that the C rated oil could damage the effectiveness of the cat. ( not a problem with most marine engines)


""""Typically, diesel engine oil will have a higher viscosity. If we were to put this higher viscosity in a gasoline engine, several problems might arise. The first is heat generation from internal fluid friction. I’ve covered before how this heat affects the life of an oil. A good rule of thumb is that for every 10 degrees C you increase the temperature, you cut the life in half.

Additive Levels

"""Diesel engine oil has more additives per volume. The most prevalent are overbase detergent additives. This additive has several jobs, but the main ones are to neutralize acids and clean. Diesel engines create a great deal more soot and combustion byproducts. Through blow-by, these find their way into the crankcase, forcing the oil to deal with them. When you put this extra additive load in a gasoline engine, the effects can be devastating to performance. The detergent will work as it is designed and try to clean the cylinder walls. This can have an adverse effect on the seal between the rings and liner, resulting in lost compression and efficiency."""
"""""""1) Diesel oil is engineered with a higher amount of dispersant and detergent package to deal with the increased amount of soot and other hydrocarbon combustion by-products present in a diesel engine. This high amount of detergent can increase the decomposition temperature of the ZDDP,3 which will reduce its effectiveness as an
anti-wear agent, especially when a vehicle is used for short trips and does not achieve a full warm-up condition.
.
2) Also, there have been some gas engine designs recently with decreased main and rod bearing clearances. These engines are specifically designed to use the lower-weight EC oils, and may experience higher than normal bearing
temperature due to insufficient oil flow, if the higher viscosity oils are used. The bearing sizes and clearances in diesel engines are engineered with this in mind, unlike gasoline engines.""""

Just a couple of excerpts from some technical papers on this subject
There are many blogs and forums on the net who also suggest that it is ok to use C only designated oils in a gas engine.
The key point is the additive package for a C class oil may work against its antiwear traits in a gas engine.
Sorry you take my comments as a contest, they are not meant to be.