Any news on gas engine CUTS?

[MHarryE]

Gasoline burns best at a 14.3:1 air to fuel ratio. When running at part power, the throttle plate us closed limiting the air entering the cylinder so when fuel is introduced the combustion will be at 14.3:1. The effect, when running at low owner, is like sucking through a small diameter straw. It takes power, in the case of a straw lung power, in an engine it is lost power. The diesel is not throttled because it is not limited to a 14.3:1 ratio. It has a clear passageway always able to breath in a full gulp every piston stroke.

Next the Otto cycle. In general, industrial engines are limited to the same peak combustion pressure. The Otto cycle has a lower compression ratio because heat, in theory, is added at a constant volume until this peak is reached, let's say 2000 psi combustion chamber pressure. That hot air expanding drives the piston down, but while it is driving the piston down the combustion chamber is enlarging and the pressure is dropping. In the Diesel cycle the air is compressed to the peak that the Otto cycle sees, and then heat is added at constant pressure. That is while the piston is descending fuel continues to be injected, combustion continues, and the combustion chamber pressure stays high. At 90 degrees where the torque of the crank throws is at the point of maximum lever arm, the piston is still giving peak push while an Otto cycle is down to half piston force. A tractor is used where this type of power is really needed, and is why they are now virtually all diesel.

Forty years ago the company where I worked, building self-propelled combines, sold the same combine with a 350 cu. in. GM gasoline engine or 292 cu. in. Allus-Chalmers turbo diesel. The gasoline engine had a higher power rating but when it came to grunt time, usually when a slug fed into the cylinder, the gas engine would promptly croak. The diesel would usually grunt and pull the slug through. In a few years the gasoline engine disappeared despite the higher power rating and significantly lower cost. After all, to handle the grunt the diesel was capable of producing, everything needed extra beef.

Things have progressed, but the Otto cycle is still the Otto cycle and has its limitations although much has been done to improve the crappy carbureted engines of the past. Gasoline still burns at 14.3:1 although mixed with ethanol that ratio changes. Engines can sense the difference and compensate, something a carbureted engine can't due without tweaking. Until the latest diesels nothing much has been done to improve their performance. Now with common rail systems and piezoelectric injectors, fuel injection can be controlled to the gnat's *** greatly improving what you can get out of each cycle. When I moved to Cat one of my first products had a 4 liter engine topping out at 107 HP. With Tier 1 we didn't have to change much and it still topped out at 107 HP. With Tier 2 we did some major redesign to the block but retained much of the original fuel system and got 133 HP. That stayed with Tier 3 when we introduced a common rail system because we were getting our feet wet. Now at Tier 4 that 4 cylinder is replacing the 6 liter 6 cylinder engine we used for our 175 HP machine - the 4 now maxes out over 175 HP. By changing from a 6 to a 4 we actually reduced the installed power plant cost. Piston ring scrub creates about 25% of the total friction so cutting 2 cylinders reduced that wasted energy. With the ability to control the injectors we can keep the combustion chamber pressure fairly constant throughout the meaningful work part of the piston stroke. Perfect? No way. Still lots of room for improvement. Would love to be like the big guys working with the GE90 powering the next generation 777X where they work with ceramics that can handle constant temperatures triple what we see.

 

[buickanddeere]

So the folks that don't care about significantly better performance don't buy the diesel....simple. Those that want the extra performance can have it...nobody is forcing them.

If they made that Cruz gasser so that it put out the same power and torque as the diesel (if possible) it would use significantly more fuel than it does now, which would make the fuel economy difference even larger than it is.

You're talking about an engine powering a tractor, but you use a Chevy Cruz engine to make your argument...that's pretty funny. Looking at the specs between those two engines, it's obvious which one would do a far better job of powering a tractor, all while getting better fuel economy....and it's not the gasser.

Diesel can cost more than gas because there's more energy per gallon in it, and the engines get more out of each gallon of diesel...again, these facts aren't news.

Are you denying that ULS diesel has cost more than gasoline per btu than gasoline since 2006?
Are you saying the either the diesel or gas Cruze uses more HP to drive down the road 55mph?
Are you saying that Uncle Bubba putting around on his rural estate on his CUT is a HD application?
Are you saying the diesel cruze is cheaper per mile to operate ?

 

[buickanddeere]

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So the folks that don't care about significantly better performance don't buy the diesel....simple. Those that want the extra performance can have it...nobody is forcing them.

If they made that Cruz gasser so that it put out the same power and torque as the diesel (if possible) it would use significantly more fuel than it does now, which would make the fuel economy difference even larger than it is.

You're talking about an engine powering a tractor, but you use a Chevy Cruz engine to make your argument...that's pretty funny. Looking at the specs between those two engines, it's obvious which one would do a far better job of powering a tractor, all while getting better fuel economy....and it's not the gasser.

Diesel can cost more than gas because there's more energy per gallon in it, and the engines get more out of each gallon of diesel...again, these facts aren't news.

Are you denying that ULS diesel has cost more than gasoline per btu than gasoline since 2006?
Are you saying the either the diesel or gas Cruze uses more HP to drive down the road 55mph?
Are you saying that Uncle Bubba putting around on his rural estate on his CUT is a HD application?
Are you saying the diesel cruze is cheaper per mile to operate ?
Are you saying that after looking at the Nabraska tests that the diesel burns less fuel in a Light Duty application than a gasser ?

As for MHarryE who is decades behind the times. The DI gasser operates at 14.7 to 1 which is a term called Stoichiometric . In fact the DI will go into a lean burn mode under some circumstances .
What is this talk of combustion occurring 90 degrees after TDC is desirable ? It's too late for efficient mechanical conversion of combustion chamber pressure to torque . Combustion that late just causes over heating as more cylinder wall is exposed to absorb heat. Ever hear tell of a gasser running hit due to retarded timing?
Ideal combustion efficiency occurs as close as possible to TDC when the combustion chamber volume is smallest.
This also gives the entire expansion stroke/power stroke to use combustion chamber pressure.
This is where common rail injection of diesels is a win as the entire load of fuel can be injected over 5 degrees of crank rotation instead of over 45 degrees rotation. Less kick back on the compression stroke as combustion is starting at 5 BTDC instead of 15-20 BTDC.
Are you aware that the DI gasser uses variable cam timing to control airflow ?
Are you aware that when a diesel , boiler fire box of gas turbine is operating at less than 100% power . The excess in throttled airflow reduces engine thermal efficiency by cooling the combustion and carrying heat out the exhaust ? Are you aware that some diesel reciprocation and stationary gas turbine applications throttle the intake to improve efficiency at less than 100% power.
Are you aware that when comparing Two similar engines such as the gas 4020 and the diesel 4020. The torque and HP is near identical? How can you compare the 292 or 350 Chev calmed to make power from 1800-4500rpm to a turbo diesel calmed shorter to make power from 1200-2200rpm?

 

[buickanddeere]

Gassers are plagued by no legal means to transport bulk fuel for them. In my area, it is against the law to transport more than 15 gallons of gasoline in marked and approved containers. That won't get me through a full day of mowing with my '46 M. Its also plagued by points and condensors, rust in the fuel tank (all my diesels have poly cells) and fouled spark plugs if not kept in tune. There's drawbacks to them all, no matter what fuels them.

Who is talking about some old M with points and a carb ? The conversation is about the cost and practicality of a DI gasser for light duty use for putting around use in a CUT. Vs the cost of gasoline -diesel fuel , the tier IV emission equipment and future emissions equipment service at the dealership.
Do you take your M to the dealer for new points ?

 

[paulfun9]

The main problem with this is we have no fuel engines built today for the use. Simply taking a gas powered engine like a 350 and changing the cams to increase the Mean cyl pressure at the intended useable RPM is not a sufficient comparison. A real test would involve building one from scratch and throwing out the rule book as most know it. Using more complex combustion chambers and off the wall bore and strokes coupled with todays computer controlled injection systems you could build one **** of a good gas powered engine for a tractor. Would it be justified between cost to build , maintain and fuel consumption? That is the real question.

 

[buickanddeere]

What is the cost between building a Tier II 35HP diesel for a CUT and a Tier IV diesel? What is glow plugs, particulate filter, EGR service and urea injection service cost going to be in 10yrsrs time ?

 

[DavesTractor]

Other than the zingers one guy on this thread keeps firing at folks, I've learned a lot about the technical aspects of the differences between modern gas and diesel engines. We should keep up this discussion, but get rid of the back and forth barbs.

Some of you guys really know your stuff and it is enjoyable to learn. It's like getting a free mechanical engineering/thermodynamics course......

 

[GManBart]

Good point. But diesel engines w the epa stuff is a thousands of dollars premium. Then the fuel costs 25-30% more per gal.

I have 3 diesel tractors, 1 gas tractor and a diesel truck. In the winter, the modern diesels start good enough w glow plugs and grid heaters. But the old gaser fires up just by choking and it's 6v! The truck tows heavy and diesels rock at that ... but... given the total cost picture, my next truck dang sure won't be diesel. Higher initial cost, higher maint costs, 25% better mpg - but 30% higher fuel cost. There is no payback that I can find.

I'm sure if they engineered a small stout gas engine for a tractor it would be popular in many diesel applications.

Last year I was pricing a new Kioti DK50SE (as they were disappearing) and a new NX 5010....the difference was less than two thousand dollars more for the NX with Tier IV, and it also had a handful of improvements that would have bumped the price without Tier IV (advanced HST and a few others). So, I don't see a massive price change with the simpler Tier IV stuff required on our relatively small SCUT/CUT/Utility tractors....not like what you see on the big machines. There is some increased cost, no doubt, but it just doesn't seem as bad as many would suggest.

The critical variable is really the fuel cost. Right now diesel is more expensive than gasoline, for a number of reasons....one be government taxes. Historically, gasoline has been more expensive than diesel everywhere, and still is in the rest of the world. Here in the U.S. that changed when refineries had to spend a bunch of money to switch to ultra low sulfur diesel, and that cost has been passed on to consumers....it's been roughly 8 years. In the last year or so the price of diesel and price of gas got closer until the recent huge drop in the price of gas. It's very possible that in a couple of years the price of diesel will be down below the price of gas again, but we'll have to wait and see.

 

[GManBart]

Are you denying that ULS diesel has cost more than gasoline per btu than gasoline since 2006?
Are you saying the either the diesel or gas Cruze uses more HP to drive down the road 55mph?
Are you saying that Uncle Bubba putting around on his rural estate on his CUT is a HD application?
Are you saying the diesel cruze is cheaper per mile to operate ?

I've already stated why diesel has cost more than gasoline for the last 8 years. When the refineries pay off all those costs associated with implementing ULSD, the price of diesel should drop below gasoline again...just like it has in the rest of the world. Don't bother saying that once they set the prices higher, they will never come down, because I saw gasoline for $1.61/Gal the other day....hasn't been that low in many years.

I never said there was a difference in HP required to move either Cruz down the road. I simply said the diesel model performs better, and if people wanted that performance, they could buy it.

I never said anything about Uncle Bubba on his CUT. You don't know anything about how other people run their machines, so basing your argument off of that is pretty weak. Some, many, folks run their tractors at rated power the whole time they operate them. No, they won't put the hours on them that a loader in a rock quarry will, but that isn't the point. Run a similar size, power, weight gasser CUT the same way, and it's not going to stand up to it, or have as good of fuel economy as the diesel....period.

I said the costs to operate the diesel Cruz will vary with the price of fuel. It gets better MPG than the gasser, and when the price of diesel drops back below that of gas, there won't be a need to discuss any of this any longer.

Your entire argument centers around one thing...that diesel costs are artificially high right now. When that changes, there really won't be much to discuss about which system has the lowest operating costs over time.

I do find it funny that people claim higher maintenance costs on diesel tractors...most folks run them for many, many years with absolutely nothing required other than filters and fluids.

 

[GManBart]

What is the cost between building a Tier II 35HP diesel for a CUT and a Tier IV diesel? What is glow plugs, particulate filter, EGR service and urea injection service cost going to be in 10yrsrs time ?

I looked at several Tier IV CUTs that didn't have DEF systems....just a DPR and EGR.