Example: Improving Operations through Optimization and Efficiencies
SCR's major advantage is its ability to deliver excellent fuel efficiency while exceeding EPA 2010 emissions standards. While specifics may differ depending upon engine manufacturer and vehicle application, using Detroit Diesel's DD15 as a base example, improvements to the cost of operations, improved fuel efficiency and near-zero emissions are reached through several steps, including: optimizing the work of the engine, reducing energy waste, an exhaust heat strategy, turbo charging, turbo compounding, a DPF regeneration strategy and a NOx reduction strategy.
- 1. Optimizing the Work of the Engine (1st law of thermodynamics) :
By controlling NOx emissions in the exhaust through SCR, the combustion process in the engine can be tuned for higher NOx output levels. This allows higher peak combustion temperatures which, in turn, leads to more heat converted to work pushing down the piston and less heat rejection via the cooling and exhaust system.
- 2. Reducing Energy Waste (2nd law of thermodynamics):
Higher peak combustion temperatures require less EGR which, in turn, leads to different channeling of the heat rejection. Meaning less wasted heat is going to the EGR cooling system and more heat is effectively utilized by the exhaust system.
- 3. Exhaust heat strategy:
The high amount of rejected heat in the exhaust stream leads to more heat for the turbo charger, turbo compound, diesel particulate filter and SCR catalyst.
- 4. Turbo Charging:
The higher amount of heat for the turbo charger leads to more fresh air entering the combustion chamber providing more oxygen to the combustion and thus enabling both a cleaner and more efficient combustion of the diesel fuel.
- 5. Turbo Compounding:
DD15, DD16 and DD13 engines were designed with Detroit Diesel's BlueTec SCR Technology in mind. This turbo compound technology converts exhaust heat into useful work turning the crankshaft to power the truck. The high rate of rejected heat in the exhaust (and not in the cooling system) due to an SCR tuned engine amplifies the effect of the the turbocompounder, converting even more waste exhaust heat into useful power.
- 6. Diesel Particulate Filter regeneration strategy :
- • The higher amount of heat flowing to the DPF leads to more passive and less active regenerations, therefore using less fuel.
- • Moreover, the higher NOx levels out of engine do not only result in higher combustion temperatures but also in lower levels of particulate matter going into the DPF. This means that the DPF needs to be regenerated less frequently, thereby needing less fuel.
- • Detroit Diesel's unique Amplified Common Rail System optimizes the diesel injection process (diesel flow rate over crank axle degrees) and leads to more effective and efficient fuel economy with low smoke production. Low smoke production means lower particulate matter creation, therefore less DPF regeneration and less fuel consumption.
- • Higher out-of-engine NOx levels allow for more DPF regenerations at lower temperatures. The result is fewer active regenerations and less fuel needed to regenerate the DPF.
- • With today's EPA 2007 technology, the active regeneration intervals are set at 325 miles. Due to the high heat, high NOx and low PM levels coming out of the engine, Detroit Diesel's BlueTec test engines are presently regenerating every 2700 miles.
- 7. NOx reduction strategy :
- • More heat in the exhaust stream means more heat going into the SCR catalyst. This in turn leads to higher conversion rates of NO and NO2 into harmless naturally occurring substances - like nitrogen and water. These higher conversion rates mean lower Diesel Exhaust Fluid consumption and allow for higher out of engine NOx levels. The improved conversion also leads to an optimized combustion process as well as improved DPF regeneration strategy.
- • Detroit Diesel chose a technology that uses Iron Zeolites in its SCR catalyst system. According to the company, Iron Zeolites offer better resistance to sulfur poisoning and therefore offer improved long term NOx reduction, low ammonia slip risk, lower NH3 oxidation capability (and thus lower Diesel Exhaust Fluid consumption) and better high temperature combustion and conversion activity.
- • With its Iron-Zeolite system, Detroit Diesel's BlueTec SCR Technology is obtaining up to 98% NOx conversion efficiency which allows it to maximize the vehicle's fuel economy potential.
As an example, Detroit Diesel's BlueTec SCR Technology has shown up to 3 to 5% better fuel economy compared to non-SCR engines planned for introduction in 2010.