Tuesday, Oct 19, 2004 at 18:00
Hi Ian,
Thanks for the detailed response. The system is electronically controlled and looks to have all the features you describe. At idle however it belts out the EGR (if I take off the intake plenum connected to the intake manifold it sounds like an open exhaust at idle and it pumps out considerable EGR). When I disconnect the EGR sensor it is wide open (after having a fidle the other day the oil light started blinking as my partner took it to work, I had forgotten to plug it back in!). Is the rover motor a direct injection job?
Below is a description of M fire I picked up of the net. Given the amount of ZD-30 failures refered to on this site I am very hesitant to do anything that may put this motor at risk. The car is a 99model and the engine number is 0000545 so I am assuming it is one of the first motors off the line in Japan.
I was actually considering fitting a pyrometer so I could
check combustion temps pre and post mods and revert back if I have to. I wonder about the sense of pumping hot EGR into the intake manifold, seems to defeat the purpose of the intercooler (even if the EGR is closed under full throttle the intake manifold would still be like an interheater.
At the very least I was going to fit an oil catch can on the breather tube to reduce the oil which combines with exhaust soot and clogs it all up.
Read on if you wish. Thanks for all the responses.
M-Fire Combustion System
Efforts to improve diesel engines have so far tended to focus on improved diffusion combustion. Nissan reasoned that NOx and soot could be reduced simultaneously if premixed combustion which is inherently less likely to produce soot could be accomplished at a low temperature. This is what M-Fire combustion achieves.
Gasoline engines produce little soot because the fuel and air are first thoroughly mixed and then ignited and burned a process called premixed combustion.
But when this process is attempted in a diesel engine, combustion takes place all at once, raising the combustion temperature and causing the formation of large quantities of NOx. To avoid that, diesel engines burn the mixture in a diffusion combustion process since the mixture is combusted as the fuel is injected, premixed combustion is controlled.
In order to prevent the mixture from burning instantaneously in this process, the combustion temperature is kept low, which works to suppress NOx formation.
However, because the fuel is ignited before it is fully vapourised, some
places in the cylinder lack a sufficient supply of oxygen, resulting in the formation of soot that causes black smoke in the exhaust.
The measures adopted to accomplish M-Fire combustion include:
optimisation of fuel injection timing;
application of heavy exhaust gas recirculation (EGR); and
generation of strong fuel swirl.
In diesel engines, fuel has traditionally been injected at a point considerably before the piston reaches top dead centre (TDC) of the compression stroke.
In the ZD30 engine, the injection timing has been changed so that the fuel is injected closer to TDC of the stroke, allowing compressed air to enter the expansion stroke, thus combustion occurs after the pressure has started to drop meaning lower pressure at the onset of combustion.
As
well, injecting fuel at this point allows ample time for fuel to evaporate because it is not ignited immediately after being injected making it possible to accomplish premixed combustion.
In designing the ZD30 engine, Nissan engineers increased the Exhaust Gas Recirculation (EGR) rate. This results in a gradual combustion process in which the mixture does not burn instantaneously following ignition, which keeps the combustion temperature from rising.
FollowupID:
340158