Killing a Diesel - a detailed how-to (much info on commonrail technology)

[instarx]

Originally Posted by Piwoslaw

Older diesels had a pump for each injector, while in commonrail technology there is one pump responsible for creating very high fuel pressure in a reservoir used by all four injectors. This, along with direct injection, gives a much better air-fuel mixture, which increases engine efficiency, power by around 25% and low end torque by 50%, reduces fuel consumption by around 20%, and reduces emissions.

All diesels, even the old ones, are direct injection.

Although a better fuel/air mix does help with common-rail injection systems, the main advantage comes from ability to fine tune the injection event. Old diesels just injected a slug of diesel into the cylinder at the appropriate time (giving that traditional diesel bang). With high pressure common-rail systems the injection period can be spread out over time - slowly at the beginning of the stroke and then pouring it on during the peak power stroke and then tapering off at the end. This wrings every bit of available power out of the stroke, resulting in more power, more torque, more efficiency, and most notably - less noise.

[Piwoslaw]

Originally Posted by instarx

All diesels, even the old ones, are direct injection.

According to Wikipedia (not that it's the only source of info...)

Indirect injection [diesel] engines were used in small-capacity, high-speed diesel engines in automotive, marine and construction uses from the 1950s, until direct injection technology advanced in the 1980s. Indirect injection engines are cheaper to build and it is easier to produce smooth, quiet-running vehicles with a simple mechanical system. In road-going vehicles most prefer the greater efficiency and better controlled emission levels of direct injection.

[oldbeaver]

Very interesting...

What if one purchase a Bosch Common Rail system complete with high presure pump, electronic control and install it in an old diesel (taking out the mechanic injection pump)?

Does a new diesel engine have special characteristics as to tolerate more pressure, more efforts, etc., from a CRDI, compared to an old diesel?

Would like to hear your comment...

Tks,

OldBeaver

Originally Posted by instarx

All diesels, even the old ones, are direct injection.

Although a better fuel/air mix does help with common-rail injection systems, the main advantage comes from ability to fine tune the injection event. Old diesels just injected a slug of diesel into the cylinder at the appropriate time (giving that traditional diesel bang). With high pressure common-rail systems the injection period can be spread out over time - slowly at the beginning of the stroke and then pouring it on during the peak power stroke and then tapering off at the end. This wrings every bit of available power out of the stroke, resulting in more power, more torque, more efficiency, and most notably - less noise.

[instarx]

Originally Posted by Piwoslaw

According to Wikipedia (not that it's the only source of info...)

Wikipedia often leaves a lot to be desired in accuracy. If you look up direct injection diesel on Wiki you get one article that says engines after 1980 were not direct injection, while the Wiki article you found says that engines before 1980 were not direct injection. The fact is, from the very first engine Rudolph Diesel built, diesels have been direct injection. Direct injection of fuel into hot compressed air in the cylinder is the main principle on which diesel engines are based.

[rmay635703]

Originally Posted by instarx

The fact is, from the very first engine Otto Diesel built, diesels have always been direct injection. Direct injection of fuel into hot compressed air in the cylinder is the main principle on which diesel engines are based.

Wrong, I believe you are mixing up what direct and indirect mean in terms of a diesel versus a gasser for example.

In a diesel Indirect injection occurs in a prechamber and was common practice on most smaller auto motors up until very recently, my 89 6.2 diesel suburban is not true direct injection for example.

On Gas motors indirect injection normally meant throttle body injection which is impossible to implement on any automotive size diesel motors that I know of and likely that is what you are thinking of, it simply can't work that way on a diesel only gas. But never the less a diesel can be indirect injection and most automotive diesels up until very recently where indirect as in having a prechamber.

Cheers
Ryan

[ecoxantia]

Absolutely right. Indirect refers to the use of a precombustion chamber. This was needed to start the combustion process in a mild manner, to avoid what would have been intolerable NVH levels in a passenger car. The first VW and Peugeot/Citroen engines from the late 1970s onwards were good examples. These engines had distributor pumps and around 175bar injection pressures.

When higher injection pressures, then better injection control, became possible, true direct diesel injection was feasible and the VW TDi was born. A bowl in the top of the piston helps swirl the mix. Early TDi still used the ditributor pump. Peugeot/Citroen and Bosch/Siemens put their efforts into the HDI, commonrail, system, which took a long time to develop. Commonrail originally had up to 1300 bar available and a small number of injection events but I think may have up to 11 shots per cycle now. HDi was released in 1999 and enabled an incredible advance in every area- as featured in Pivoslaw's car, the 307. VW meanwhile went the PD route to get high pressures - for a while. That got them 2000 bar. Now VW group have ditched PD for commonrail - for lower emissions, I understand.

How do I know all this? Been driving diesels since 1990 and just swapped a HDi engined car for a noisier PD-engined one!

Please excuse my ignorance of lots of other diesel car makers - my slant on it is that VW and Peugeot/Citroen (or Bosch, Siemens and Delphi) led the way and others followed. For example, Ford have teamed up with Peugeot/Citroen for their commonrail diesels. (You really didn't want to drive a Ford-engined Ford diesel in the 1990s!)

Simon

=

Originally Posted by rmay635703

Wrong, I believe you are mixing up what direct and indirect mean in terms of a diesel versus a gasser for example.

In a diesel Indirect injection occurs in a prechamber and was common practice on most smaller auto motors up until very recently, my 89 6.2 diesel suburban is not true direct injection for example.



Cheers
Ryan

[Piwoslaw]

Quick update: Earlier I wrote that I unplugged the crankshaft position sensor and nothing happened. Well, it turned out that that wasn't the sensor I thought it was. (In fact, I still don't know what I was unplugging earlier.) After going over hard to find engine wiring diagrams I finally found the crankcase sensor, and it does kill the engine (and throws a code if I disconnect it while the car is moving). Unplugging only the camshaft sensor still doesn't kill the engine, only prevents it from starting - the ECU synchronizes it with the crankshaft sensor at start up, so if it gets unplugged later the crankshaft sensor takes over.

[jakobnev]

On my gasser the injectors have a common +12v-line and all their separate ground wires go to the ECU that connects each wire to ground when it wants fuel to be injected through that injector. If your injectors have a similar setup, you could kill the engine by simply interrupting the common +12v-line.

[Piwoslaw]

Originally Posted by jakobnev

On my gasser the injectors have a common +12v-line and all their separate ground wires go to the ECU that connects each wire to ground when it wants fuel to be injected through that injector. If your injectors have a similar setup, you could kill the engine by simply interrupting the common +12v-line.

In certain engines (HDi's for example) both leads of each injector go to the ECU. This is because the injectors double as induction coils for increasing voltage to the required 50V-80V.

[colonelk]

My (extremely old skool) Isuzu engined diesel has an engine stop solenoid which is how it stops the engine when you turn the key off. I was going to energise (or de, Ive got to check the wiring) this via a switch. Should be easier for people with older technology like me