Vmcrdrod wrote:
I had been reading on VGT and egr working togeather and had a question as far as fueling during egr operation.
The way I’m visualizing this process is that:
1, the egr opens the fcv butterfly either isolates the intake from the charge air system or tapers its flow.
2, The computer somehow accounts for this change orienting the vanes to reduce turbine input and boost press/flow
3, The fueling is changed at this point to accomidate for the a less dense air charge and the combustion somehow resumes in one way or another.
Question:With the egr path removed as well as the fcv deleted durring these events when the computer believes that it is operating the egr pathway, is there a possibility that the air charge in the cylinders is high and leaning out the mixture causing cylinder temps to elevate above design parameters?
The way I’m visualizing this process is that:
1, the egr opens the fcv butterfly either isolates the intake from the charge air system or tapers its flow.
2, The computer somehow accounts for this change orienting the vanes to reduce turbine input and boost press/flow
3, The fueling is changed at this point to accomidate for the a less dense air charge and the combustion somehow resumes in one way or another.
Question:With the egr path removed as well as the fcv deleted durring these events when the computer believes that it is operating the egr pathway, is there a possibility that the air charge in the cylinders is high and leaning out the mixture causing cylinder temps to elevate above design parameters?
When you reintroduce exhaust gases back into the diesel engine intake, you are displacing incoming air that is rich in oxygen with exhaust gasses that has little or no oxygen. As a result, the engine doesn’t burn all the injected fuel because there is less available oxygen to support combustion. If anything, the ECM would lower fuel injection rates when the EGR valve is open due to knowing there is not enough oxygen to support complete fuel combustion. But I think most of us are of the opinion that the ECM was not programmed to do this.
Feeding soot laden exhaust gases into the intake of a diesel engine makes engine combustion less efficient, compromising economy and power. The normally "dry" intake system of a diesel engine is now subject to fouling from soot and oil vapors, which can effect or limit total airflow into the combustion chamber. When EGR soot is combined with the oil vapors from a positive crankcase ventilation (PCV) system, it will cause buildup of sticky gooey tar in the intake manifold and on the valves. It can also can cause wear problems with other engine components i.e. rocker arm rollers, bearings, etc. Diesel EGR's also greatly increases soot production leaving the engine's combustion chambers due to incomplete combustion caused by the lack of sufficient oxygen for complete combustion. EGR systems also add abrasive soot contaminants and will increase engine oil acidity, which in turn will reduce engine longevity.
The effects of EGR operation in a diesel engine reduce fuel economy and engine output power an estimated 3% to 5% which means an additional 3%-5% more diesel is consumed and burned to generate the same amount of power.
Is the EGR valve needed? NO, but HECK NO! The EPA does not give a rats behind about engine efficiency or engine longevity. It was all about lowering NOX and they could have cared less about the effects on economy, power, and engine life. And in reality, since it (EGR) causes an increase of 3 to 5% increase of fuel consumption which in turn increases emissions, do they even really care about the environment, really makes you wonder. Was it really simply all about power and control?
