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'HEAVY-DUTY GASOLINE ENGINES'
Pages 47-72

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From page 47...
... For this reason, the control technology used on current light-duty engines is a useful source of information on techniques for meeting future, more stringent regulations on heavy-duty engine emissions. Control Techniques Emission controls for gasoline engines are based on engine modifications and/or the addition of exhaust-treatment devices such as catalytic converters.
From page 48...
... However, this lowers fuel economy and performance. Exhaust Gas Recirculation Introducing exhaust gases into the intake charge lowers peak combustion
From page 49...
... 49 Stoichiometric Air/Fuel Ratio Exhaust „ Temperature Rich Lean AIR/FUEL RATIO Figure 7 Schematic illustration of the dependence of emissions and other engine parameters on air/fuel ratio. Vertical scale is linear; the curves show the relative variation in the indicated parameters for a typical engine.
From page 50...
... In engines without emission controls, the overall ratio is usually set rich enough to ensure that the leanest cylinder will have a ratio rich enough to provide adequate performance. Modifications to the intake system that improve the cylinder-to-cylinder uniformity of the air/fuel ratio allow the overall ratio to be set leaner without impairing other engine performance parameters.
From page 51...
... Although the above correlation equation for NOX is an estimate at best, it does give a rough indication of how an engine with a given NOX emission level on the steady-state cycle will perform on the transient cycle. Examples of Current-Production Low-NOx Engines Table l7 shows data for Chrysler heavy-duty gasoline engines for the l98l model year.
From page 52...
... The numbers by the data points are arbitrary engine identifiers, used also in Figures 9 and l0 (California Air Resources Board, l98l)
From page 53...
... 50 25 I I I J 0 10 20 30 40 50 60 STEADY-STATE CYCLE CARBON MONOXIDE EMISSIONS (g/bhp-h) Figure 9 Comparison of carbon monoxide emission data taken with the transient and steady-state test cycles.
From page 54...
... UI X O z o u 55 2 oc 11 •3 I I I I "024 6 8 10 STEADY-STATE CYCLE N0X EMISSIONS (g/bhp-h) Figure l0 Comparison of NOX emission data taken with the transient and steady-state test cycles.
From page 55...
... bThe 360-3 engine is designed for more severe use than the 360-l engine. SOURCE: Informal communication, Chrysler Corporation, April l, l98l.
From page 56...
... The International Harvester engine uses a rich mixture, rather than EGR, to lower NOX emissions. Two air pumps, one for each exhaust bank, are used to control the carbon monoxide emissions that result from rich operation.
From page 57...
... Noncatalytic NOX Controls Figure ll represents schematically the systems used for noncatalytic NOX emissions control. As explained earlier, these can include recalibration of air/fuel ratios, rescheduling of ignition timing, and introduction of EGR.
From page 58...
... 58 Carburetor Calibration Ignition Advance Schedule EGR Typical Factory Single Exhaust System Figure ll Noncatalytic emission control (Hansel, Cox, and Nugent, l98l)
From page 59...
... 3 0.59 5.04 3.03 259 EGR No. 4 0.67 5.97 2.9l 254 SOURCE: Informal communication, General Motors Corporation, February 4, l98l.
From page 60...
... Catalytic Control of NOX Emissions Catalytic reduction of NOX emissions, using three-way catalyst systems similar to those used in late model passenger cars, is being considered for gasoline-powered, heavy-duty vehicles. As shown in Figure l2, these systems can take several forms, involving either single three-way catalyst beds or combinations of three-way catalyst beds and downstream oxidation catalysts to enhance control of hydrocarbon and carbon monoxide emissions.
From page 61...
... , Hydro- Carbon Reduction in With Percentage Change carbons Monoxide NOX NOX Emissions in Parentheses 350-mV Control Pointb No 4.64 43.5 8.04 322 (26.7)
From page 62...
... 62 Oxygen Sensor TWC Single-Bed or Dual-Bed Catalysts Oxygen Sensor Air Oxidation Catalysts TWC Single-Bed or Dual-Bed Catalysts • To Air Meters Microswitch Oxygen Sensor TWC Catalysts Oxidation Mufflers Catalysts Figure l2 Catalytic NOX emission control systems (Hansel, Cox, and Nugent, l98l)
From page 63...
... , the three-way catalytic converter can yield NOX emissions of l-2 g/bhp-h with fresh catalyst. However, for this particular installation, with air-fuel ratio adjustments in the indicated range, it was necessary to add a downstream oxidizing catalyst bed to control emissions of hydrocarbons and carbon monoxide.
From page 64...
... 64 TABLE 20 Emissions of Heavy-Duty 350-Cubic-Inch-Displacement V-8 Gasoline Engine with Catalytic NOx Control System Engine Characteristics Emissions and Fuel Consumption (g/bhp-h) l984 Prototype 350-CID V-8 with Dual Oxidizing Converters Hydro- Carbon Fuel carbons Monoxide NOX Consumption Without EGR 0.47 4.0l 5.65 245 With EGR 0.67 5.97 2.9l 254 l986 Prototype 350-CID V-8 with Three-Way Converters and EGR Full-time air 0.36 8.l4 l.97 259 Modulated air 0.54 ll.66 l.28 259 SOURCE: Informal communication, General Motors Corporation, February 4, l98l.
From page 65...
... Engine Configuration Hydro- Carbon Fuel Increase in carbons Monoxide NO Consumption Fuel Consumption3 l978 Production 2.58 56.0 4.89 3l2 0 350 millivoltsb Three-way catalyst with EGR 0.85 l3.9 3.l4 328 5.2 Three -- way catalyst with oxidation catalyst and EGR 0.74 3.46 3.45 337 8.2 530 millivolts Three-way catalyst without EGR l.4l 22.9 l.58 320 2.6 Three-way catalyst with oxidation catalyst and EGR 0.64 3.2l l.48 32l 2.9 630 millivolts Three-way catalyst with oxidation catalyst and EGR 0.56 3.29 0.7l 335 7.3 740 millivolts Three-way catalyst with oxidation catalyst and EGR 0.68 3.60 0.74 3l9 2.3 Percentage change compared with l978 production engine. ^Carburetor set point (350 mV - lean; 550 mV = chemically correct; 630 mV - rich)
From page 66...
... A number of factors are responsible for the relative severity of heavy-duty service, but the most important by far is the potential for excessively high catalyst bed temperatures, leading to deterioration in catalyst activity. Such concern has been voiced with regard to deterioration of the oxidation catalysts required to meet l984 hydrocarbon and carbon monoxide standards, as well as the three-way catalytic converters needed to meet the proposed l986 NOX standard.
From page 67...
... 67 Upstream 1 Inch Behind Front Face Downstream Upstream 1 Inch Behind Front Face Downstream Oxygen Sensor Location 15OO F 14OO°F 153O°F 146O°F TWC Cata1yst 137O°F 1575°F 145O°F 1310° F167O°F 1750°FOxidation Cata1yst 1320°F 1510°F 14OO°F Maxima During MAP Test I Maxima > During Heavy-Duty I Transient Test Figure l3 Maximum catalyst temperatures (Hansel, Cox, and Nugent, l98l)
From page 68...
... A 1OOO° F 2000° F 12 16 20 24 36 AGING TIME (h) B Figure l4 Effect of furnace aging on three-way catalyst hydrocarbon removal efficiency, after 600-second warmup: (A)
From page 69...
... (Informal communication, General Motors Corporation, February 4, l98l.)
From page 70...
... Among these are the questions of satisfactory engine performance and durability (exhaust valve and valve seat life, octane satisfaction, maximum power output, fuel distribution, and driveability. In addition, manufacturers have expressed serious concerns about the durability of the oxidation catalysts used to meet l984-l986 hydrocarbon and carbon monoxide emission standards.
From page 71...
... The higher EGR rates and retarded timing required for lower NOX levels would further increase fuel consumption and at the same time reduce engine performance. With fresh catalysts, one three-way catalytic control system has hydrocarbon, carbon monoxide, and NOX emissions of 0.54, ll.66, and l.28 g/bhp-h, respectively, with an accompanying 5-percent increase in fuel consumption relative to that of a prototype system with an NOX level of 6.5 g/bhp-h.
From page 72...
... l98l. "Public Hearing To Consider Amendments to Title l3, Section l956.7, California Administrative Code, Regarding Exhaust Emission Standards and Test Procedures for l984 and Subsequent Model Heavy-Duty Engines." Sacramento, Calif.: California Air Resources Board.


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