A little question about diesels

haze
Ive no idea, But I do believe the Tdi has a centrafugal oil cleaner which removes the carbon allowing greater time between oil changes (20,000km ?)
Cheers Bob

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Haze,
The reason they generate more soot is because they are a less efficient motor (at burning the available fuel) and hence contaminate the oil quicker, with unburnt fuel and the by-products of incomplete combustion. No engine burns up all the fuel completely, some just do a better job than others ie. direct injection motors. The higher the compression ratio of the motor generally the more efficient it will be and that's why most new high tech diesels are DI. That is also why an indirect injection motor relies so heavily on its glow plugs for cold starts because the compression ratio is lower than that of direct injection motors. The reason why we have Indirect injection is a little beyond me, but they are a quiter motor because the combustion phase is spread over a longer time period and hence no loud "knock" or rattle like a direct injection. The other thing that will soot the oil up is how hard the engine is being worked. If the motor is working hard and at near max revs (like your D7 should be!!) then this is where the efficiency of the motor is at its best and hence will burn cleaner than a diesel being putted around town in the old ute. Diesels love to be worked hard so that all the old bleep e that builds up can be burnt off.

But generally DI is the way to go and correct me if I'm wrong readers but I think you'd be hard pressed to find too many new diesel model vehicles that are indirect injection other than the old 1HZ, in the cruisers. Anyway better stop now, hope this helps Haze.

Cheers,
Hughesy

I'm no expert either, but my understanding is that common rail system is better again, because it is not limited by a mechanical fuel pump. There's only so much control you can get with a mechanical fuel pump, regardless of whether it's direct or indirect injection. In contrast, the high pressure rail allows the computer to put exactly what it wants in the combustion chamber at precisely when the cycle needs it. I've also heard that some can inject at multiple points in each combustion cycle. Hence more power and more complete burning - and hence cleaner oil..... Please correct me if I'm full of ####.....Russell S
Prado RV6

In short, here's the low down for Direct Injection and Indirect Injection.

DIRECT INJECTION:

Advantages.
1. As all the air is compressed within the cylinder and all combustion occours therein, the heat losses are not great and a high thermal efficiency is obtained
2. Due to low heat losses the engine can be started from cold without the necessity of heater plugs
3. Good fuel economy is obtained due to the high thermal efficiency

Disadvantages
1. Rough running due to high cylinder pressures caused by delay fuel accumulating in main cylinder
2. Ignition value of fuel is very important as this affects delay period
3. Relatively small nozzle orifices which are more prone to blockage
4. Higher injection pressures cause more rapid wear of injection equipment

INDIRECT INJECTION:

Advantages.
1. Poor quailty fuels can be burned as the high pressure at the end of the delay period does not operate on the piston
2. The engine runs very smoothly due to the low maximum cylinder pressure.
3. High compression ratios to 22:1 can be used without excessively high cylinder combustion pressures.
4. Low injection pressure used, also pintle type nozzles which reduce injection system maintenance

Disadvantages.
1. Considerable combustion occours away from the cylinder therefore a lower thermal efficiency is obtained and poor fuel economy results
2. Glow plugs must be used in order to facilitate cold starting
3. High compression ratios must be used to compensate to heat loss

-Stuart

Haze
Some motors are ment to run dirty (like jap non direct diesels) they have a large filter to catch the crud and a 5000km change, others like the American direct inj motors have small filters and a service interval of 10-30000kms.
The precombustion chamber is solely there to mix air and fuel so it can be ignited.
Direct injection relies on smaller injecters to atomise better and the compression heat ignites the charge.
Go the D7
Andrewwheredayathinkwer mike?

Now you blokes have really given me some stuff to get my head around! So ok, a lower C/R direct injection doesnt need glow plugs to fire, but a higher C/R indirect does. But I have to think about that little slot that leads into the pre comb. chamber and relate it to the output from my little air compressor ie: where the compressed airflow is restricted it gets as hot as all getout! Why isnt that hot enough to light the wick? - obviously not. And when it does (finally) ignite it dont want to burn completely anyway. It does seem sensible to whack the fuel in where its needed,smack on top of the piston, so have the "indirect injection" proponents been selling us a dud? (always been happy with the chatter of the tdi, now thinking about the purr of the 1hz!) As to the D7G, it has a fuel pump which primes the injection system which in turn is actuated by the camshaft. A governer controls injection rate. Not sure if this is "common rail" but certainly no electronics involved. Now 8500+ hrs. and never touched. Uses 1-3l. oil in 150hrs. Yeah! go the 7!!
I now feel a need for some deep reseach (plus a rum or 3)
Once again, thanks, haze

Has this got anything to do with 'Explor Oz'...or are you using this site as a forum for self promotion ? Why don't you contact the fuel companies if u are fair dinkum ??

Bit touchy hazey????

Waynepd. Bought the 1hz new so no prior history to consider. Its a workhorse and often (ie Very often) is towing heavy loads - like 8 drums of fuel in a tandem trailer. And seemingly quite typical of toyota, plenty of black smoke following behind. I wondered what might happen if I turned the injector pump back a whisker, and so the result its possibly down a bit on power, the smoke is all but gone (can still be seen from the lights of a following vehicle) but best of all the oil is nowhere near as dirty at 5k. as previous. No noticable change in economy, around 14l./100km. towing, but speeds are down probably 10%. What the hell! we still get there.
cheers haze

Thanks, old jack. Good one. I note the spec. is tdc. I checked with a home made pipe to fit no.1 injector and to get what I reckoned was injection start I had to advance the pump 2deg. Does this make sense? Does it smoke with more advance or retarded. I have a feeling these jap motors get their claimed HP (kw.) from a fair bit of over fuelling? Thanks
cheers haze