Effects of Low-Purge Vehicle Applications and ... - MeadWestvaco

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portion of the canister carbon bed closest to the atmosphere port. EFFECT OF CARBON HONEYCOMB ON CANISTER WORKING CAPACITY As a result of testing for canister bleed emissions performance, it was discovered that activated carbon honeycombs have a significant positive impact on diurnal canister working capacity. The effect of the activated carbon honeycomb on canister gasoline working capacity is summarized in Figure 7. Canister G W C (g) . 180 160 140 120 100 80 60 40 20 0 +4% +11% +13% +19% No HCA 29x100-200 41x150-200 50x150-200 Heated 41x150 Figure 7. Effect of activated carbon honeycomb on canister working capacity. The baseline gasoline working capacity of 138 g presented in Figure 6 was obtained with a 2.1-liter canister filled with BAX 1500 without an activated carbon honeycomb attached. An increase in overall canister working capacity of 4% to 19% was demonstrated with the addition of an activated carbon honeycomb. The increased capacity was proportional to the honeycomb size and therefore the capacity of the honeycomb to adsorb hydrocarbon vapors. EFFECT OF ETHANOL FUEL BLENDS ON CARBON BED PERFORMANCE Adsorption of Ethanol The adsorption and desorption isotherms for Ethanol and Butane on BAX 1500 at 25°C, is shown in Figures 8 and 9. Loading g/g Carbon 1.40 1.20 1.00 0.80 0.60 0.40 0.20 Adsorption Desorption 0.00 10 100 1000 10000 100000 1000000 Concentration (ppm) Figure 8. BAX 1500 Butane Equilibrium Isotherm. Loading g/g Carbon 1.40 1.20 1.00 0.80 0.60 0.40 0.20 Adsorption Desorption 0.00 10 100 1000 10000 100000 1000000 Concentration (ppm) Figure 9. BAX 1500 Ethanol Equilibrium Isotherm. Comparisons of these figures clearly show that, at equal concentrations, ethanol is more readily adsorbed than butane, the standard used to evaluate automotive carbons (3, 4). More importantly, due to the mesoporous nature of MeadWestvaco automotive carbons, the desorption curves show that ethanol and butane are readily removed from the carbon pores. Ethanol Fuel Blends There are two potential ways for ethanol to be present in fuels: 1. Splash Blending. This is the straight addition of alcohol to a non-alcohol-based gasoline. This has been shown to significantly affect the vapor pressure of the resultant mix as shown in Figure 10 (5).
Reid Vapor Pressure @ 37.8oC (kPa) . 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100 Ethanol Concentration (%) Figure 10: Effect on Vapor Pressure by ethanol addition to 9.0 RVP Fuel Figure 10 shows that splash blending of ethanol up to approximately 40% will cause an increase in the vapor pressure of the resultant blend. 2. Blending to a fixed Vapor Pressure. This is the addition of an ethanol to gasoline fuel that has been altered so that the resultant solution has the same vapor pressure as the unblended gasoline. For example, in the case of Fuel - 6, the volatility of the non-ethanol components of the fuel is reduced to compensate for this effect of adding ethanol. Regardless of the approach used, the most important property of the fuel blend with respect to activated carbon canister performance is the vapor pressure. The vapor pressure, rather than ethanol content, determines the resultant diurnal vapor generation from the fuel tank and therefore the required working capacity of the carbon canister. Diurnal Vapor Generation A range of fuels was tested for vapor generation rates by following the diurnal test procedure of subjecting a fuel tank and canister to the entire two-day CARB diurnal temperature profile as described earlier. The RVP of the fuels tested ranged from 34.5 to 62.1 kPa, with an ethanol content of 0 to 85%. The diurnal vapor generation results are shown in Figure 11. Average Daily Vapor Load (g) . 40 35 30 25 20 15 Fuel - 1 Fuel - 3 Fuel - 4 Fuel - 2 Fuel - 5 10 20 25 30 35 40 45 RVP (kPa) 50 55 60 65 70 Figure 11. Diurnal vapor generation of fuels tested As would be expected, this figure shows a strong relationship between RVP and vapor generation. More importantly, it shows that fuels of equivalent RVP will generate similar total amounts of diurnal vapors regardless of the ethanol content. For example, on the average Fuel -2 generated 27.5 grams of vapor compared to an average of 29.7 grams for Fuel - 3 with an equivalent RVP. While similar total vapor generation amounts have been observed for fuels with similar RVP, it is understood that the fuels may have different volatilities at the various temperatures experienced during the CARB diurnal temperature profile. Based on these results, if a canister is properly sized for use with a 62.1 RVP fuel, it should be adequately sized for ethanol blends of an equal or lower RVP. EFFECT OF ETHANOL FUEL BLENDS ON HONEYCOMB PERFORMANCE Initially, simulated diurnal testing was conducted using standard Fuel - 5 and Fuel - 3 as specified by CARB procedures for non-Flex Fuel Vehicles (FFV’s) to establish baseline performance. Results obtained using the 2.1-liter canister filled with BAX 1500 both with and without a standard 41x150 honeycomb (Configuration A) attached under these conditions were compared to those obtained by cycling with the same Fuel - 5 followed by a two day diurnal using Fuel - 2. The results are compared in Figure 12. Day 2 Emissions (mg) . 180 160 140 120 100 80 60 40 20 0 BAX 1500 w / 41x150 HCA BAX 1500 Cyc Fuel - 5 / DBL Fuel - 3 Cyc Fuel - 5 / DBL Fuel - 2
Page 1 and 2: Copyright © 2007 SAE International
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