Posted on 5/28/2007, 4:08:34 AM by P-40
The Bosch Group anticipates increasing sales of its common-rail diesel direct injection technology by nearly 18% to more than eight million systems in 2007, up from 6.8 million last year. Bosch alone has equipped more than 33 million passenger-car and commercial-vehicle engines with this technology since 1997.
Ten years ago, Bosch was the first company to put a common-rail system for passenger cars on the market. The first vehicles to feature the technology were the Alfa Romeo 156 JTD and the Mercedes-Benz 220 CDI.
In conjunction with turbocharging, the injection system has helped the diesel engine achieve a market breakthrough to approximately 50% of the new car market in western Europe. Ten years ago, diesel’s share was only 22%. The diesel engine’s main selling points are its reduced fuel consumption and lower CO2 emissions, combined with a much cleaner emissions profile than before.
Since the early 1990s, carbon monoxide, nitrogen oxide, and hydrocarbon emissions from new diesels have been reduced by 95% and more.
Our common-rail technology will play a major role in meeting the future Euro 5, Euro 6, and US07 Bin5 exhaust emission standards. As a result, the combination of common-rail technology and exhaust-gas treatment is securing the future of the diesel engine. —Dr. Ulrich Dohle, president of the Bosch Diesel Systems division
In 2006, Belgium had the highest percentage of diesel engines with a market share of 74%, followed by France (71%), Spain (68%), Portugal (65%), Austria (62%) and Italy (59%). In Germany, 44% of all new passenger cars had a diesel engine.
Bosch expects the market share of diesel-powered light-duty vehicles in the US to increase from its current level of approximately 6% to 15% in 2015. Bosch also expects rapid growth in Asia.
This year, Bosch plans to sell about 100,000 common-rail systems in both India and China. By 2013, it is likely that there will be some 1.3 million such systems in each of these countries. At present, just one-fifth of the company’s total production of high-pressure injection systems is for the markets in Asia and the Americas, but by 2015 this figure will be nearly 50%.
Bosch currently supplies common-rail systems with injection pressures of 1,350, 1,600, and 1,800 bar, using both solenoid-valve and piezo-valve technology. The next step—2,000-bar systems—goes into series production before the end of the year.
At the same time, Bosch is developing more cost-effective common-rail systems with an injection pressure of 1,100 to 1,450 bar for emerging markets such as India or China. They are primarily intended for the low-price vehicle segment, and will be launched at the end of 2007. For the middle market segment, Bosch is developing new systems in order to gradually reduce costs and fuel consumption.
OK, for the laity: what’s common rail?
It is a way of delivering fuel to the cylinders efficiently and in a way that results in less pollution.
Instead of using a low pressure fuel pump with individual lines and fuel injectors, it uses a common high pressure system and individual solenoid valves.
I know, cars and trucks got rid of carburetors long ago but bikes soldier on. I am amazed at how it starts instantly, runs great whether hot and dry or cold and wet, and saves a lot of gas.
And this is with 1985 technology. Can't wait to get a fuel efficient diesel sometime soon. Then the inevitable $5 fuel won't seem like such a big deal.
I understand common rail systems, but I’m unfamiliar with piezo-valve technology.
Diesel engine injection pumps run some pretty high pressures. As an extreme example, {if I'm remembering this right, heheh} a 1970's 343 Caterpillar [turbo-charged, inter-coooled, in-line six cylinder 350 h.p.] needs 365 PSI to 'trip' the injector. That's some pretty big ft. lb. numbers!
Most other diesels get by with less, I think...
The big difference between the gasoline, and the diesel sytems, is the much higher pressure needed for diesel applications. THAT, I am very certain of.
Are you familiar with diesel injection pumps? One pump, with as many fuel lines as there need be...six cylinder has six, eight has eight, etc.
Ordinary diesel injection pumps, have multiple, mechanically driven valves [with corresponding, individual fuel lines], each timed identically to open at something near top-dead-center on each separate cylinder's compression stroke;
The "common rail" systems discussed in the article, control timing (and metering) at each individual injector, feeding from the same fuel line, as opposed to the "injection pump" type of diesel, which can only "meter" the amount of fuel, not readily change the timing.
To invision the one common fuel line, that has as many shorter fuel lines branched off of it as there are injectors, think of a ladder that has the proper number of rungs [or steps], but is missing one [of two] side rails. Laid upon it's side, it could look a little like;
_____/__/__/__/__/__/____
the bottom 'line', being the common rail, the upright " / " marks being the spliced in shunts, going to separate injectors, each of which have their own individually controlled metering/timing valve. The ability of this type of system to change the timing of injection, along with more ordinary, simple metering of what amount of fuel is to be injected, as it relates to engine 'load', rpm, etc., enables the engine to be highly "tuned" or adjusted to meet the need, on the fly, as it were.
As something of a side note, which may be confusing to some, I recall that old style Detroit Diesel 2 stroke engines use a "common rail", but fuel is metered differently, purely mechanically, with the last bit of "push" to trigger injection given by a plunger, also mechanically driven, in this latter instance, by push rod and tappet. Pretty nifty, for 1930's technology.
There are still more than a few of those type of engines in service, though they are a vanishing breed. I know of one old V-1271 Detroit ("V" configuration, 12 cylinders, 71 c.i. per cylinder) that runs (uh, roars?) like a top.
Somewhat more modern, 4 stroke diesels have long used injection pumps. Neither of these two older types above, by themselves, can readily use subtle changes in injection timing to enhance performance.
Gasoline engines of the more "performance" variety, have long used systems similar to this "common rail" that is discussed in the article, but dealing with much, much lower fuel pressures. A certain '89 Pontiac Firebird with so-called 'Tuned Port Injection', that just rumbled away from where I'm presently, at comes to mind...
Quote from the article, with bold highlight on a very 'key' word;
Bosch currently supplies common-rail systems with injection pressures of 1,350, 1,600, and 1,800 bar, using both solenoid-valve and piezo-valve technology.
Think --- pressurized system --- with individual 'valving' to both meter the amount, & time the exact moment of injection. For gasoline, it was easy. Well, at least for Bosch, it was easy. lol
The higher pressures needed for diesel engines, have proved to be much more challenging to designers.
I'm no expert. Hope this helps.
Piezoelectric ceramics are layered structures which expand when a voltage is applied to them. They are very fast and offer extremely precise control. They are also reliable if packaged correctly. Used in fuel injectors, they offer more precise volume and timing control of fuel delivery, providing better mileae and emissions.
OK, diesel basics:
Diesel fuel has to be pushed into the injectors at high pressure. The higher the pressure, the more uniform and finer the fuel spray into the cylinders.
The old diesel fuel systems used a pump that injected fuel into each injector individually. Without getting into picky details, each injector has a steel fuel line back to the fuel pump (sometimes called the “fuel rack”), which pressurizes each injector individually. The injector pump is responsible for metering the amount of fuel, pressurizing the fuel and timing when the fuel is injected.
OK, then we get to the Cat/Navistar “HEUI” system, where the fuel injection is controlled by the fuel injection computer, and the injector is opened/closed with very high-pressure crankcase oil, used as hydraulic fluid. This allows for more precise control over the timing and duration of the injection cycle. In some variants of this type of system, the very high pressure crank oil is also used to transfer some of it’s pressure to the fuel prior to injection — in effect, a mechanism within the injector boosts the fuel pressure behind the injector.
Next development we get to is common rail system. In the common rail system, the “common rail” is a common fuel “bus” off which there are taps going to each individual injector.
On each injector, there is a piezoelectric crystal inside the mechanism that is used as a valve to allow fuel to the injector. The modern piezo injectors allow for highly precise fuel injection, including such techniques as “split shot”, where there isn’t just one burst of fuel injected, but actually a series of smaller fuel bursts injected into the cylinder. This technique is used to reduce emissions and quiet injector “cackle” and diesel engine noises.
Executive summary: common rail and piezo injectors are the future of diesel fuel systems.
When we’re comparing the old mechanical racks to the common rail systems, the old racks are now “low pressure” — even at 350+ PSI.
Delphi is fielding a common rail system that produces fuel pressures over 25,000 PSI. That’s one of the secrets to these common rail systems — they’re jacking the pressures way up, in a quest to get the most efficiently burning fuel cloud out of the injector.
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