NOX Emission Controls for Heavy-Duty Vehicles Toward Meeting a 1986 Standard (1981) / Chapter Skim
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'HEAVY-DUTY DIESEL ENGINES'
'HEAVY-DUTY DIESEL ENGINES'
Pages 21-46
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From page 21... ...
Thus, on an overall but not necessarily a local basis, combustion takes place under lean conditions, and carbon monoxide is readily oxidized to carbon dioxide; carbon monoxide emissions are therefore not a significant problem in diesel engines. Initially, some of the injected fuel evaporates and undergoes a series of chemical reactions leading to ignition.
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From page 22... ...
The energy released by combustion heats any unburned fuel, which then undergoes chemical reactions in an oxygen-deficient atmosphere; these reactions are the start of the formation of particulate matter. Although there is some uncertainty about the exact mechanism of particulate formation in diesel engines, it is generally agreed that the chemical reactions occurring in this oxygen-deficient region form species that can react to form large molecules.
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From page 23... ...
Exhaust treatment of gaseous diesel emissions is difficult because of the low temperatures and large oxygen concentrations. Because the three-way catalyst that is used in gasoline engines depends on having very small amounts of oxygen in the exhaust gases, it cannot be used to remove NOX from diesel exhaust.
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From page 24... ...
report on lightduty diesel engines show a l0- to l5-percent improvement in fuel economy due to improved injection systems. The committee contacted technical experts involved in developing these systems, who reported improvements in this range when the latest generation of mechanical controls were replaced by electronic systems.
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From page 25... ...
o_ I I I I J 8 10 246 TIME (s) Figure l Acceleration of a turbocharged diesel engine against a steady load, showing the trade-off between responses and exhaust smoke (experimental data)
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From page 26... ...
In general, reducing charge temperature decreases NOx formation by reducing combustion temperatures. Modifying Engine Designs While no dramatic breakthroughs are expected, some changes in design details can reduce emissions.
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From page 27... ...
There are substantial questions about catalyst durability, and the design of an adequate system is a serious challenge. Water Injection Water, injected in emulsion with the diesel fuel, is known to reduce NOX emissions with little increase (and possibly some decrease)
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From page 28... ...
l986 AVAILABILITY OF CONTROL TECHNIQUES NOX control techniques likely to be available in time to meet l986 emission standards include variable injection timing and pressure, charge cooling, and possibly exhaust gas recirculation. It is not clear whether electronic control of injection timing will be available by l986; some systems may be on the market by that date, but whether they will have been available long enough to meet engine development, testing, and production lead times is uncertain.
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From page 29... ...
Such data are useful for engineering analyses of promising control options, but there is no established correlation with results from the new transient test procedure, especially at low NOX and hydrocarbon emission levels. With the new transient test procedure, preliminary data suggest significant variation in results from laboratory to laboratory.
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From page 30... ...
30 2.5 |0 2.0 ^o O w 5$ LU ££ OQ O O £T QC CO Q < ^ UJ 12 1.0 0.5 0.5 1.0 1.5 2.0 2.5 HYDROCARBON EMISSIONS (g/bhp-h) MEASURED ON STEADY-STATE CYCLE Figure 2 Correlation of hydrocarbon emission data taken with the transient and steady-state test cycles
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From page 31... ...
MEASURED ON STEADY-STATE CYCLE Correlation of NOX emission data taken with the transient and steady-state test cycles
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From page 32... ...
32 CO iH 3 O 4-1 oo o in ^ oo P*
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From page 33... ...
These NOX emissions levels from current production engines compare with uncontrolled diesel engine NOX emissions of ll-20 g/bhp-h; that is, Federal standards have cut NOX emissions by about 20 -- 50 percent, and California standards by about 40-75 percent. Uncontrolled NOX emissions from heavy-duty diesel engines were one and one-half to three times the uncontrolled gasoline engine emissions baseline of 6.8 g/bhp-h recently established by EPA.
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From page 34... ...
i^ « C m "• ^ •* Sout hwes t Sout hwes t 79 Research Research rtlf 1 cat Ion Institute Institute -Mode 13-Mode Transient NO' NONu «••> s s ^ *
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From page 35... ...
35 TABLE l4 l980 NOX Levels for Diesel Engines Certified for Sale in California (May l980) NOX l980 Control Certification Transient System NO*
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From page 37... ...
37 k i 01 CO ,O -LJ | 8 CM CM CM CM CM CM CM CM CM CM ^fj NO CO GO O O rH in OO -*
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From page 38... ...
ki O -H ra -o :cd 4-1 O O.rHO Z CO ki 01 | • ki CO 01O.
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From page 39... ...
Figure 4 shows that reducing NOx emission levels below about 8 g/bhp-h results in fuel economy penalties that increase as NOX levels are lowered. For example, technology under development shows a fuel consumption penalty of about 4 percent at NOX emissions levels of 5 g/bhp-h, relative to the same technology at NOX levels of 8 g/bhp-h.
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From page 40... ...
10 NOX EMISSIONS (g/bhp-h) , MEASURED ON Figure 4 STEADY-STATE CYCLE Fuel consumption vs emission level
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From page 41... ...
4l •gS IF 2 55 h- O ^2 _ _/ c < 0 Ja A Production Engines • Prototype Engines 2 4 6 8 NOX EMISSIONS (g/bhp-h) AS MEASURED ON TRANSIENT TEST CYCLE TO Figure 5 Particulate emission level vs NOX emission level
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From page 42... ...
Solid circles represent data taken with the transient test cycle, and open circj.es represent data taken with the steady-state test cycle.
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From page 43... ...
Hydrocarbon emissions rise as reductions in NOX emissions become substantial. The hydrocarbon emission levels of different engines and NOX emission control systems vary widely.
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From page 44... ...
Only modest additional NOX control can be achieved without fuel economy penalties at lower hydrocarbon and particulate emission levels than those currently being achieved. The more promising emission control techniques being developed show that low-mileage NOX emission levels of 6 g/bhp-h on the transient test cycle can be achieved with engine-out particulates emissions of 0.5-0.7 g/bhp-h and hydrocarbon emissions of 0.7-l.4 g/bhp-h, and with a fuel consumption penalty of 2.5-4 percent.
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From page 46... ...
l980. "Draft Regulatory Analysis, Environmental Impact Statement and NOX Pollutant Specific Study for Proposed Gaseous Emission Regulations for l985 and Later Model Year Heavy-Duty Engines." Office of Mobile Source Air Pollution Control.
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