Gasoline/diesel fuel mixtures?

[Number21]

I'm sitting here bored out of my mind recovering from some surgery, googling stuff. I came across this article from the University of Wisconsin:
http://www.news.wisc.edu/16945

They claim to be running a modified Cat engine on a varying mixture of diesel and gasoline. They also claim to have achieved more than 50% thermal efficiency doing this. I'm wondering if any such idea could be applied to a generator?

I'm a little bit confused how they implemented the system. It says:

"You can think of the diesel spray as a collection of liquid spark plugs, essentially, that ignite the gasoline," says Reitz, the Wisconsin Distinguished Professor of Mechanical Engineering. "The new strategy changes the fuel properties by blending the two fuels within the combustion chamber to precisely control the combustion process, based on when and how much diesel fuel is injected."

That makes it sound like a compression ignition engine. But then it says this:

In addition, the system can use relatively inexpensive low-pressure fuel injection (commonly used in gasoline engines), instead of the high-pressure injection required by conventional diesel engines.

How would that work? Anybody else ever heard of this technology before? I thought maybe they were using gasoline in the same way some people use propane or natural gas to fog their diesel engine. But how could that work using "low pressure fuel injection"? The diesel pilot would have to be the normal high pressure system, wouldn't it?

[billswan]

here is another newer link http://phys.org/news/2014-07-best-ever-efficiency-green-gas-diesel.html

Billswan

[Number21]

Interesting. They do say it is compression ignition.

High efficiency is only one benefit of the RCCI system. To burn cleanly, conventional diesel engines pressurize the injected fuel up to 3,000 times atmospheric pressure. The RCCI system, working at 300 atmospheres, offers a major cost saving.

I suppose when they said "low pressure" injectors it must have been relatively speaking.

Is this basically similar to propane/natural gas injection on a diesel engine? Or am I reading it wrong? Has anybody here ever experimented with using gasoline that way?

[quinnf]

Sounds eerily familiar to what was posted by a farmer on the other forum years ago.  He swore up, down, and sideways that by adding 10% regular unleaded gas to his diesel, he was achieving crazy efficiency, like 50% more fuel left in the tank after he finished plowing, than with straight diesel.   

[mobile_bob]

i have read about something similar some years ago
iirc the details, i think this is what they are doing

by using an injector out of a gas engine, such as a port injection bendix/bosch style
typical of car gas engines, they use it to inject a predetermined amount of gasoline into the port

the limit here is injecting just enough to remain lean enough to not detonate under the heat of compression

then a smaller amount of diesel is injected via the high pressure injector and that charge is used much like pilot injection for a dual fuel engine application, so

instead of putting natural gas into the intake and using the diesel injector to provide pilot injection to initiate combustion... the replace the nat gas with injected gasoline.

the trick is this, in my opinion

to do this right, you need to have an electronic diesel injector and also the port injector and a special computer than can calculate the injections timing and determine the amount of each fuel injected for the rpm and load being serviced.

in charles lafayette taylors twin books on the internal combustion engine,  MIT did some testing years ago with a much less sophisticated setup on a stationary single cylinder diesel test stand engine and iirc they were able to exceed something like 45% thermal efficiency, which was huge give most engines of its displacement were hard pressed to get over about 32% on a good day.

to answer the question, that is if i remember the question, yes i think maybe this could be done
in a stationary engine, maybe even successfully, but likely not to the level of success that the engine reportedly did...

if you have a steady state, steady rpm and steady load such as a generator and a fixed load, it would be much easier than a variable load, and much much easier than variable speed and variable load applications.

it might be done with one of those aftermarket injection modules to control the gas injected into the intake port. those modules are laptop programmable, so you could tailor the amount of gas delivered to something well under the detonation limit and work up... and use the mechanical injection as is for pilot injection much like a fumigation scheme.

one you get a fair idea of what the pulse width needs to be to provide the right about of gasoline
or rather a safe amount and get the best efficiency, i suppose you could then replace the module with a microcontroller... or maybe even start with a micro controller or find a single cylinder programmable module (megasquirt maybe) and work up something interesting.

in taylors books he relates that gasoline as a fuel if it could be injected into a diesel engine could result in significantly higher thermal efficiencies than running on diesel fuel.  i never really dug into it that much at the time, but i do recall reading a lot about the subject, but not enough to remember or understand the reasoning behind why gasoline would be more efficient a fuel in such an application?

clear as mud?

bob g

[Number21]

Great information. I love this forum, I think if I asked this question anywhere else it would start an argument. LOL

I love the idea of using an aftermarket type fuel injection computer, that just might work! But if this is the same basic theory as natural gas or propane injection, is there any reason gasoline would work better than propane? I wonder if this would be a good use for stale gasoline - its not hard to find somebody that wants to give away an old tank of gas out of their boat or something.

Does anybody know if a smaller propane injected diesel engine could ever reach 50-60% thermal efficiency claimed by the gasoline injected diesel engine?

[quinnf]

Gasoline burns relatively slowly and consistently with a relatively slow flame front speed.  Same with methane, but propane burns faster and less predictably.  Sir Harry Ricardo's book, "The High Speed Internal-Combustion Engine," available for $215 from Amazon, or for 35 lbs. ($52 U.S.) from http://estore.ricardo.com/shop/the-high-speed-internal-combustion-engine/ discusses fuel and everything else you want to know in much more detail than you would have thought possible.  It's worth poring through, though it's not an easy read. 

Propane injection is touchier to implement than is natural gas (methane) injection at the high compression ratio of a diesel engine because at high pressures the fuel and oxygen molecules are much closer together than they would be at lower pressure.  Thus, the fuel/air mixture burns faster, which isn't a good thing for efficiency or for the life of the mechanical components.  However propane works fine as a fuel in spark ignition engines at low compression.  I played around with it enough to convince myself that the ugly noises coming from the cylinder probably weren't good for the engine.  Ricardo has photographs of the flame front in his book, which is worth the price just to learn how such things are done. 

Whatever you do, you're going to have a hard time getting that kind of thermal efficiency out of something like a 'roid than you will out of a larger engine partly because of heat loss due to the small size of the engine.  Note that the numbers the Wisconsin group reported were normalized to 59% "in a truck engine." 

[quinnf]

Oh, and if you want to start an argument, just tell Bob you want to erect wind turbines in his town (ducking!).   

Quinn

[Number21]

Whatever you do, you're going to have a hard time getting that kind of thermal efficiency out of something like a 'roid than you will out of a larger engine partly because of heat loss due to the small size of the engine.  Note that the numbers the Wisconsin group reported were normalized to 59% "in a truck engine."

The article seems a bit confusing. The first part says this:

The one-cylinder test engine in the basement of a University of Wisconsin-Madison lab is connected to a life-support system of pipes, tubes, ducts and cables. You might think that the engine resembles a patient in intensive care, but in this case, the patient is not sick.
Instead, the elaborate monitoring system shows that the engine can convert 59.5 percent of the chemical energy in its fuel into motion—significantly better than the 52 percent maximum in modern diesel truck engines.

But then it says:

Our study demonstrated 59.5 percent efficiency in a truck-size engine

Are they calling this Cat engine a "truck sized engine"? If they can get that efficiency in a single cylinder Cat, I can't see why you couldn't come close with a listeroid.

Is this single cylinder Cat engine they are using some sort of research only machine? I can't find much reference to any giant single cylinder Cats, I didn't know there was such a thing.

[mobile_bob]

those cat single cyl engines are "research" engines

the issue as i see it with lister/oids or any other engine of small hp and massive amounts of iron
is one of heat loss.  its very hard to get much increase in efficiency from and engine with so much iron to power ratio.

there are other issues that play a smaller roll too.

still might be fun to give it a try?

of course i would suggest using a changfa/oid or some other small package engine that can run at higher temperatures and conceivably reject less heat to start with.

just thinking outloud here.

bob g

Quinn,  ya back at  ya buddy! 

[Number21]

the issue as i see it with lister/oids or any other engine of small hp and massive amounts of iron
is one of heat loss.  its very hard to get much increase in efficiency from and engine with so much iron to power ratio.

Isn't that basically what the Cat engine is though? From the little bit of vague information I found on it, it seems really similar to a lister or any other big old flywheel type engine.

Definitely something I would like to experiment with. What is the normal efficiency of a listeroid? Are they even 30%?

[quinnf]

A research engine is an instrumented test engine whose characteristics are very well known.  Data gathered from running such an engine can be mathematically scaled to predict the performance of a specific fuel and running condition in a larger real-world engine.   That's what I think they meant by their predicting 59.5% efficiency in a truck-sized engine.  The Cat test engine generated the data.  The data was then scaled, knowing the efficiency of the test engine, to predict what would happen in a larger real-world engine.  

A 6/1 is maybe 25% efficient, in terms of BTU (fuel) in vs. KW out from an ST-type generator.  The generator is maybe 80% efficient, so figure 25/0.8 = 31% efficient, but that's probably optimistic.  It's not a particularly efficient engine because of the small displacement and large mass of iron that wicks away heat.  While combustion temperature and exhaust temperature of a 'roid are about what one would expect for a naturally aspirated compression ignition engine, that's not the whole story.  Hotater reported that his long-running 6/1 had trouble getting the crankcase oil temperature above about 115 degrees F.  That's not optimal for efficiency.  And remember that it's an 85 year old design that came into production in the latter days of the age of steam.  

A good example of an efficient engine would be any of the gasoline engines that are used in hybrid cars like the Prius.  It's compact, multicylinder, with a multivalve head with variable valve timing, huge air intake manifold cross-section, and it uses a modified Atikinson cycle, in which the compression stroke is shorter than the power stroke.  That's achieved via valve timing rather than through complicated mechanical linkages, as in a true Atkinson cycle engine.  So pumping losses are reduced compared to a standard Otto or Diesel cycle engine.  Wikipedia has a great animation which shows the concept.  The current generation Prius engines have a thermal efficiency of over 40%.  Current thermal efficiency of the largest IC engines are those used in large ships, which are over 50% efficient.  http://www.emma-maersk.com/engine/Wartsila_Sulzer_RTA96-C.htm

http://en.wikipedia.org/wiki/Atkinson_cycle

Quinn

[Number21]

The current generation Prius engines have a thermal efficiency of over 40%.

That's amazing, I didn't realize they made gasoline engines that efficient. I read something about Honda using new single cylinder Atkinson cycle engine in their small cogenerators and they claim a 15% increase in efficiency. I always wondered why they didn't put a diesel engine in a Prius, I guess that is why.

Purely hypothetical question:
What if you wrapped a listeroid with insulation and ran it at 250F coolant/oil/fuel temperature? Would thermal efficiency be increased?

To be honest I'm considering building my own "research engine" from scratch. Something like this little model from the Wikipedia article on Atkinson engines:
http://en.wikipedia.org/wiki/Atkinson_cycle#/media/File:Atkinson-cycle_engine.jpg
I'd love to do some efficiency experiments on different fuels and compression ratios and ignition methods.

[Number21]

I found another article about this with a little more clear information:
http://articles.sae.org/8388/
To me it sounds like they more or less took a diesel engine, added port injected gasoline with a computer program, and that's about it.

The dual-fuel experiments took place in a single-cylinder version of a heavy-duty Caterpillar diesel truck engine

Researchers at the University of Wisconsin perform dual-fuel engine experiments on a modified 2.44-L Caterpillar 3401E heavy-duty, single-cylinder diesel engine. The Engine Research Center team installed a port fuel injection unit and a common-rail injection system as well as some novel sensing instrumentation.

Is this a standard inline 6 or V8 engine with just one cylinder? Seems like the efficiency should be the same no matter how many cylinders.

Other interesting quotes:

Engine operations would depend on the load: high load—90% gas, 10% diesel; low load—90% diesel, 10% gas; idle—100% diesel.

In one test with the truck engine at the 9-bar (130-psi) operating point, NOx and soot were 0.012 g/kW·h and 0.008 g/kW·h, respectively, while achieving 53% net indicated thermal efficiency.

Engineers at Oak Ridge National Laboratory (ORNL) have tested a multicylinder dual-fuel RCCI engine (a modified four-cylinder, 1.9-L European GM diesel), said Robert Wagner, Acting Director of the Fuels, Engines, and Emissions Research Center there. The efficiency improvements are not as large as the single-cylinder power plants, he said, because of the increased complexity of multiple cylinders—turbocharging, a real EGR system, cylinder-to-cylinder and cycle-to-cycle losses.

[buickanddeere]

Breaking the 50% efficiency mark  in a cost effective mobile application other than marine applications is near impossible. Even thermal fossil electrical power plants struggle to exceed 50%. Claims of 59% are over the top.