Mixing diesel with petrol
 

I saw something about a new engine design that combines petrol and diesel to give better performance.

Has anyone tried adding some diesel to their petrol engine?

Some engined can make use of low octane fuel, ones that can widely vary the cam timing.
I wouldn't try it as most gasoline engines depend on knock resistant gasoline.
Probably better off with lean burn and the search function because we know both of those things work.

Some “back of the hand” calculations to debunk this myth that adding diesel to gasoline(in a gas car) to gain economy...

Gasoline is 120,405 BTU/US gal and diesel fuel is 128,700 BTU/US gal, or ~11% more than gas...
Since the two fuels are formulated for the opposite forms of combustion, we’ll assume diesel has an “octane rating” of 0

If you mixed 5% diesel (for ease of math) into 93 octane, non ethanol fuel, you’d end up with a fuel that could be supposed to then have an “octane rating” of 88, which will run in most gas engines. Averaging the BTUs of the fuels, your new mixed fuel would contain 120,820 BTU/US gal, or 0.34% more than standard pump gas...

You’d have to be measuring your distance to the meter, and your fuel to the gram(or mL), in a controlled laboratory environment, to be able to maybe see any gain in efficiency from fuel alone, and this is ignoring any potential negative effects on catalyst efficiency, or the slightly enhanced lubricity of the fuel...

In addition, you’re now mixing 93 octane non ethanol fuel which I’m betting is at least a dollar more than regular unleaded, with on road diesel, which is usually on par price wise with premium unleaded, to make a fuel that no high compression or high boost engine will tolerate...

Can we call this myth, “BUSTED”, yet?

In NZ, until recently, unleaded was double the price of diesel. Petrol gets heavily taxed at the pump, while diesel users pay a tax per km. In theory, if you could go 51% petrol, 49% diesel then you would save 25% overall. But diesel gets 35% better mpg, so you would need to add another 17% to your km/$ figure. Australia is similar I think.

Can we call this myth plausible yet?

Except you're off by an order of magnitude on the amount of diesel you can add. So no.

It wasn’t fair of me to consider thatfuel prices abroad aren’t necessarily the same as they are here in WV... I will still assume that higher octane gasoline will cost more than regular...

Best possible case scenario, you live at a really high elevation, and are not bothered by the cost of obtaining race fuel... with 100 octane unleaded race fuel, and at an elevation of a mile or more, you *may* get away with 15% diesel(85 octane at that point) and have a lower compression engine live... but the fuel would still only be about one percent more energy dense than gasoline and any gains from that would be really hard to quantify, and here in the US, race fuel costs more than $7 a gallon, or double the cost of diesel...

Diesel engines get ~30-35% better mileage than an equivalent gas engine because the Diesel combustion cycle is more thermally efficient than the Otto combustion cycle, NOT just because the fuel is more energy dense

Okay, fair enough, but he painted over Alaska, lol

I watched an episode of fifth gear
https://youtu.be/GL9-i9tcESU and the guy put diesel in a petrol car and petrol in a diesel car to see what happens. In both cases they ran for quite a long time. So even 100% works (with possible damage) so I'm not buying that there is a maximum mixture. Where did you get this data anyway?

The question still has not been answered: has anyone tried it?
https://youtu.be/pCr6bjQMrgU

Don't do it. It stinks!!!

I googled the energy densities of the two fuels. I did have to guess that diesel has 0 octane rating, based on the fact that an Otto cycle engine and a diesel cycle engine use the opposite forms of combustion, I couldn’t find a rating...

I guessed at the ratio to still keep the mixture at at least 87 AKI octane, to prevent definite engine damage, averaging diesel in at 0 octane... if it were, say, rated at 60, things would change some, in that you could run more diesel in gasoline and still have a mixture average of 87, but it wouldn’t boost the energy density of the resultant fuel enough to bother with, IMO... if mixing some diesel in makes the fuel mix cheaper than straight gasoline, then it could be a feasible option for reducing your fuel bill but I don’t believe it will boost efficiency enough to see from tank to tank

Interesting.
The only use I have heard of is opposite - to add few liters of petrol into full tank of diesel so you have some antifreeze protection...

Bad logic, as diesel will not combust entirely and will emit stinky white smoke in a gas engine. Nobody behind you will like you.

...add a little DDT and you've got a "Mosquito Spraying Fogger" vehicle.

I have not tried it.

But damage is not just possible but almost inevitable, on a time horizon too near and at a price too dear for anyone on a normal budget and in need of their car on a daily basis.

I watched the "Engineering Explained" vid you linked to as well. But I think he implicitly answers the question of whether this is a good mod for a standard road car in his explanation. The engine he describes was was specially designed with dual ports for differently timed injections of the two fuels. It also had a super high 16:1 compression ratio and outlandishly lean AFRs programmed into the ECU, such as 45:1 at times.

So, I would never try it on my car. I would not expect more than a marginal benefit in engine efficiency from just mixing diesel with gasoline in a conventional gasoline engine. I would expect engine damage, the likelihood of which would depend on how radical you are in the mixture.

Yes it has been answered

This guy

Had run a diesel gas mix for years, bigger engines from around the early 2k era work the best.

As for a “FLEXBOOST” Diesel those usually independently inject a diesel “spark plug” to ignite another fuel like e85 or CNG.

This requires separate tanks and a control system, works very well to give a naturally aspirated diesel both fuel economy, simplicity, emissions and power,
Sadly it appears unlikely to happen due to things called laws which have different emissions requirements for diesel or gasoline which would make a real dual fuel beast aftermarket at best,

ah well.

the number is 15 not 0
otherwise it would spontaneously combust
and the diesel engine is more efficient because of 0 throttling AND higher calorie fuel as well as a very long stroke and lean mix.
it all adds up

its simple really

if you want more miles per tank do it
if you want more miles per dollar don't

I mentioned Jason Fenske's explanation in this thread: http://ecomodder.com/forum/showthrea...cci-36404.html

After googling around I found that propane (and possibly natural gas) kits for diesel engines were a real thing, mostly used for more power (and inevitable damage) but could (barely) increase efficiency. I was mainly interested in natural gas as it is relatively abundant right now in the USA.

These systems don't appear to have near the control of control over the propane inserted into the airflow and don't appear to have much more control over the existing ECU (presumably the driver adjusts the air-fuel ratio with his right foot as you start with a diesel engine).

If you wanted to get the effects from the RCCI research, you would probably have to hack a megasquirt to handle two complete ignition systems (probably buy two and have a master/slave system where the diesel megasquirt gives the gasoline one specific fuel injection levels and otherwise ignores it).

If it works at all I'd expect to see it in commercial trucks. I'd expect them to deal with adding fuel from two pumps for a 20% increase in fuel efficiency, followed by truck stops having gas/e85 next to diesel pumps at truck stops.

My guess is that existing propane kits are unlikely to increase efficiency enough to bother without heavy megasquirt hacking. How much you are into that is up to you. One other interesting thing is that most of the research centered on a single RPM: this is close to commercial truck practice, but also of interest to solar enthusiasts who want generator backup. Presumably 1800 rpm would be ideal (you really need 3600, but you could design the generator with more poles or possibly gear it. The efficiency of 1800 should outweigh the gearing issue).

That's because he couldn't ignite the lean gas mixture unless he squirted some diesel in. This was done on LP powered locomotive diesel engines in the 80s.