Propane injection for diesel.

It would be interesting to see more on this optimum compression ratio issue. If anyone has any good papers on the subject lying around, feel free to post them.

From basic thermodynamics, the overall cycle efficiency of the air-standard Diesel cycle is easily derived. It is:
eta = 1 - 1/(r^(k-1)) * [ 1/k * (rc^k - 1) / (rc - 1) ]
= eta_Otto_cycle * [ 1/k * (rc^k - 1) / (rc - 1) ]
with
eta = efficiency (of air-standard Diesel cycle with constant-volume heat addition)
eta_Otto_cycle = efficiency (of air-standard Otto cycle with constant-pressure heat addition)
r = compression ratio
k = specific heat ratio
rc = cutoff ratio

From which we see that the theoretical Diesel cycle increases in overall efficiency (indicated, not brake, since we're talking only about the cycle) as the compression ratio increases. We also see that the Diesel cycle is inherently less efficient than an Otto cycle of the same compression ratio. (The efficiency advantage of the modern diesel engine over the modern gas engine is due to its much higher compression ratio- the composition or energy density of the fuel is not a factor in the calculation of thermal efficiency.)

Of course, the actual modern CI engine is better approximated by a dual-cycle model. But these are just models- they're a good starting point for comparison, and they give us a good idea what to expect, but they don't tell us everything that's happening.

The paper by Ratnakara et al. that 'kerosene' posted earlier found that, with their particular variable-compression test engine, fuel consumption and smoke production were minimized, and brake thermal efficiency maximized, for r=14.8. Note the reason they found for the declining performance at higher compression ratios:

Most research I've seen that suggests problems with high-compression diesel engines explains poor behaviour at high compression in a similar way. Although the cycle is inherently more efficient at high compression ratios, other factors- such as charge dilution, charge velocity, valve timing and overlap, residual gas, etc. can cause problems at higher cylinder pressures, increasing fuel demand and compromising efficiency. Take the derivative of the equation above and it's easy to see that, as you crank up the compression ratio, you quickly run into the 'law of diminishing returns'- each successive increase in r produces ever-smaller increases in eta, increases that can easily be overwhelmed by other factors.

The optimum compression ratio will not necessarily be the same for all engine architectures or operating profiles. Open chamber designs, for instance, tend to run better at lower compression ratios than pre-chamber designs. There will of course be lower peak pressures in a lower-compression engine, thus reducing stress on the parts as well as reducing the tendency to sound like there's a leprechaun with a hammer in each cylinder.



Those nitrous oxide systems for street-race cars have been effectively banned around here. (You can transport them, but the system and bottles must be disconnected.) It seems the fire departments were getting tired of having the things explode (and when they go, they pack one hell of a whallop) in collisions or as the firefighters were trying to extract the drivers from crashed street-race cars.

 

Marsh,
I think the big problem with diesels is that the engine companies, because of the bureaucrats, have been focusing on emissions and not efficiency. The interesting thing is that a ultra-efficient diesel will burn less fuel than a gas engine or even a low-emission diesel, but all the development goes into low-emission. A case in point is two-stroke diesels, they were starting to computerize and really make these puppies sing. Then the whole thing was canned because of emissions.

As a young hot rodder, I learned quickly how to get a motor to put out more power, but at the cost of emissions. I had 200hp four cylinder pontiac firebird that flew, and got really good gas mileage. Now we are asking engines to produce power, be fuel mizers, and have low emissions.

More power can mean less fuel if you run motor slower.

On nitrous, I saw a intake manifold on a v8 break off an engine, go through a hood, and twenty feet away. Now a days with correct setup that wont happen, but care is necessary, especially when you start engine. Nitrous would freeze valves and then leak slow into engine when off, then when you turn on engine... Well Boom...

 

Ontario loses about 6000 to 9000 people a year to smog and air pollution. 2100 of those deaths are in Toronto alone, most of the rest in the surrounding cities. We have about 16,000 to 20,000 patients a year treated in hospital for smog-related illnesses. So when our bureaucrats clamp down on engine manufacturers, factories, cement plants, and everything else, saying "you must cut your emissions by xxx"..... that's why. There are just too many engines, too many factories, too many power plants in too small a space. (And we don't really set our own emissions regulations- we just copy California's from a few years earlier.)

Back to the topic....
It's interesting to look at long-term trends in engine design. The Ford Model T had a whopping 20.2 hp and consumed 11 to 19 L/100km (13 to 21 mpg). My ten-year-old Hyundai Elantra has about 130 hp and uses 7 to 9 L/100km. 6.5 times the power with half the fuel. Yet, fleet-wide, we're not using any less fuel per car than we were back then. Most of the engine performance and efficiency gains we've made in the last century have been used for increased power (>200 hp in a compact sedan? WTF?) and to make cars bigger, faster and heavier for the same amount of usable space (Lexus RX, I'm talking about you). Serious work on emission control is a relatively new phenomenon- EGR and PCV systems date back a few decades, but most of the emission controls we take for granted today have only been around for 10 to 25 years. Had we devoted the same effort to efficiency and emissions over the last 70 years as we have devoted to cramming more power into a given size of engine bay, who knows where we could be.

But I'm getting away from the real topic, which, IIRC, was about spraying combustible liquids into the intake of a diesel....

 

My point exactly, so if you build your diesel like a hot rod. More flow, compression, more air, ported heads, more fuel, less restrictive exhaust, blueprint it. Make it faster, more rpms, then you have what BMW and MB have done. More HP per CC, more reliability and greater performance and fuel economy.

Anyway, Propane is to diesel like Nitrous is to Gas engines. It can enhance the power, but the better built the engine the better it will make it.
Oh one thing about Nitrous, we also had to inject raw gasoline(fuel) into intake to compensated for extra oxidizer.
Interesting will be to inject Nitrous(oxidizer) and Propane (fuel) into diesel.
Otherwise injecting propane only will be limited by amount of oxygen already in engine in air.

 

Think he (Sasha) meant modern "chip controlled" Diesels (Iron).

He was able to get a completely unwilling "Skoda" engine of about ?70? ltr. displ. 1550 hp, back into service, using soap, wire, and a hammer! USSR!

Regards
Richard

 

Chip the iron -> sounds to me like bore and/or stroke it for more displacement.... with the obvious loss of durability that may come from the resulting thinner, more highly stressed block.
Computer controls ought not to diminish the life of the block... if anything, they ought to improve it (less carbon deposits, better temperature control, etc.).... but the computer itself, and the 100-odd sensors and actuators it's connected to, well, we all know what happens to the VISA card when they go bad.

 

They do, be shure.
I cannot recall the figures of a very impressive study i´ve seen in the 80 ies, showing that the lifespan of a (hughe) ships diesel is narrow connected to the mass involved! As I remember B&W MAN had the longest lifespan followed by "Wärtsiläa", "Sulzer" and all the conglomerates, simply due to the fact: they had more "combustion related" mass (not housing and basement) than for example "Pielsticks" and "Mitsubishi".

Just a thought.
But one of the commercial side (I guess)

Regards
Richard

 

You've said a mouthful here, given that the architectural details turn out to be much more important than the simple mechanical compression ratio, or even the effective ratio.

There are a plethora of pre-chamber designs, many that use lower compression ratios. And the presence or absence of diesel knock is difficult to even relate in a casual way with such broad design families as 'pre-chamber' and 'open chamber'. After all, knock is simply the result of the delay of the onset of combustion, such that all or nearly all of the fuel charge has entered the chamber before the combustion event begins. A low compression engine may knock terribly at low speeds and light loads, if the onset of combustion is delayed.

Among the characteristics of any pre-chamber design is the conservation of combustion heat in a specific area within the cylinder (the pre-combustion chamber) in order (among other things) to ensure that there is no delay in the onset of combustion, the major cause of diesel knock.

Many use a 'glow bar', which retains a low 'red hot' state during operation. Such designs often depend on glow plugs to start since the glow bar won't be hot when the engine starts cold.

These measures are designed to get the charge burning with a lower effective compression ratio by causing super-atomization and turbulence. The goal is to mitigate the differences in combustion onset that normally occur under differing conditions of load and engine temperature.

Have a look at the Maybach 'M' pre-chamber desgn. Also look at the Lanova energy cell.


Jimbo