November 7, 2016
On October 19, 2016 the Web site Diesel Net published a valuable updated summary of U.S. NTE (not-to-exceed) engine emission testing requirements.
The US EPA has introduced not-to-exceed (NTE) emission limits and testing requirements as an additional instrument to make sure that heavy-duty engine emissions are controlled over the full range of speed and load combinations commonly experienced in use.
NTE testing does not involve a specific driving cycle of any specific length (mileage or time). Rather, it involves driving of any type that could occur within the bounds of the NTE control area, including operation under steady-state or transient conditions and under varying ambient conditions. Emissions are averaged over a minimum time of thirty seconds and then compared to the applicable NTE emission limits.
Heavy Duty Engines
The NTE approach establishes a control area (the “NTE zone”) which represents engine speeds and loads expected to be encountered in normal operation and use by diesel heavy-duty engines. It consists of the following engine speed and load points.
All engine speeds 15% above the ESC (European Stationary Cycle) speeds:
nlo + 0.15 × (nhi – nlo)
nhi = the highest engine speed on the power curve where 70% of the maximum engine power is still achievable,
nlo = the lowest engine speed on the power curve where 50% of the maximum engine power is still achievable.
1. All engine load points greater than or equal to 30% or more of the maximum torque value produced by the engine.
2. All operating speed and load points with brake specific fuel consumption (BSFC) values within 5% of the minimum BSFC value of the engine. The manufacturer may petition to exclude any of these speed and load points where the engine is not expected to operate in normal vehicle operation. Engines equipped with drivelines with multi-speed manual transmissions or automatic transmissions with a finite number of gears are not subject to this requirement.
3. All speed and load points where the power produced by the engine is less than 30% of the maximum power produced by the engine are excluded.
The NTE cycle also has several temperature exclusions:
1. For engines equipped with exhaust gas recirculation (EGR), operation within the NTE control area is not subject to NTE emission limits during cold temperature conditions. Cold temperature operation is defined as engine operating conditions meeting either of the following two criteria (Figure 2):
i. Intake manifold temperature (IMT) less than or equal to the temperature defined by the following relationship between IMT and absolute intake manifold pressure (IMP) for the corresponding IMP:
IMP = 0.0875 × IMT – 7.75
IMP = absolute intake manifold pressure in bars,
IMT = intake manifold temperature in degrees Fahrenheit.
ii. Engine coolant temperature (ECT) less than or equal to the temperature defined by the following relationship between ECT and absolute intake manifold pressure (IMP) for the corresponding IMP:
IMP = 0.0778 × ECT – 9.8889
ECT = engine coolant temperature in degrees Fahrenheit.
For engines equipped with one or more aftertreatment devices that reduce NOx or NMHC emissions, the NTE NOx and NMHC emission limits do not apply when the exhaust gas temperature measured within 12 inches of the outlet of the aftertreatment device is less the 250°C. For multi-bed systems, it is the temperature at the outlet of the device with the maximum flow rate that determines whether the NTE limits apply.
What this means to you
EPA ‘s not-to-exceed (NTE) emission limits and testing requirements are an additional instrument to make sure that heavy-duty engine emissions are controlled over the full range of speed and load combinations commonly experienced in use. DieselNet has published a valuable updated summary of NTE testing requirements.
MIRATECH can help
Contact MIRTECH to learn more about emission solutions for your stationary engines.