Interpreting Mirenco MDEP Reports
Mirenco MDEP reports consist of two plots, a MIR 120-second 5-Gas Transit Procedure (we’ll call it a 5-Gas Report), and a DPM Evaluation (DPM Report).
Understanding the DPM Report (Diesel Particulate Matter, which is unburned particles of diesel fuel) is fairly straightforward; higher percentages mean that higher amounts of unburned diesel particulate are being blown out the exhaust stack. DPM under 15-16 is not visible, while 16 and over it is visible as black smoke. A DPM rating of 95-99 is what one would expect at a diesel truck-pull or tractor-pull. In an underground mine, lower DPM is better, because men are breathing DPM, and for both above and below ground applications, lower DPM means fewer gallons per year are going out the exhaust stack.
The 5-Gas Report is more complex. Looking at a 5-Gas Report, there are 5 segments, going from left to right. The first segment is with the engine at low idle, with the gas probe in outside air…it lasts for about 30 seconds. The second segment is with the engine at low idle with the probe in the exhaust stack and is about 15 seconds long. The third segment is engine at high idle with the gas probe still in the exhaust stack for 30 seconds. The fourth segment is the gas probe still in the stack, but the engine returns to low idle and lasts 15 seconds. The last stage is with the engine at low idle, the gas probe back out in the outside air and lasts 30 seconds.
The important part of this test is the third (middle) segment of the test. The first and last segments are basically confirming that the test is valid by measuring outside air…the 5-Gas lines should be the same at 0 seconds as they are at 120 seconds. The lines in the second and fourth segments should be about the same, because they are measuring exhaust at low idle.
Looking at the third segment, the CO2 line should be above the CO line…this indicates good combustion…if the CO line is higher, poor combustion caused by injector problems or air restriction caused by dirty air filter(s) or by poor turbocharger performance are indicated. The black HC (hydrocarbon) line should track along the bottom of the graph…if it wanders up to 10 or more, it indicates too much raw fuel being injected or engine oil being burned (leaking turbocharger seal or too much oil coming up past the rings).
The bright red line (NOx) indicates advanced or retarded timing…on a 2-stack engine (D-11R, 992), compare the position of the NOx line from one bank to the other…if one bank is much higher, it indicates that one or more cylinders in that bank are working harder than the cylinders in the other bank (could indicate valve lash problem in the bank with the lower NOx reading). A very high NOx line indicates the engine timing is too advanced.
The green O2 line starts out at 21 in the first segment, dips a bit to about 18 in the second segment, dips to about 16-17 in the third segment, then back to about 18 in the fourth segment, and goes back to 21 in the last segment.
Spikes that run off the chart going from the second segment to the third segment show that too much fuel is being injected too quickly as the engine accelerates to high idle; extending the rise time on the C-Max / D-Max controller will usually bring these spikes down considerably.
The smoke trail number that is recorded confirms levels of HC and overfueling…higher smoke trail indicates raw, unburned fuel being blown through the engine, engine oil being burned, etc.; lower smoke trail numbers indicate good combustion with little or no overfueling.
In underground applications, MDEP interval should be about 4 months…above ground the interval should be about 6 months.
Although the target market for C-Max and D-Max installations is larger, heavily-loaded midlife engines, experience has shown that DPM levels can be dropped considerably on new engines and on newly-rebuilt engines. Controlling overfueling means less fuel wash down of the lube oil film on cylinder walls, extending engine life.