ULEVs

The main converter, which is located downstream of the EHC, heats to functional temperature much more quickly because of catalytic combustion of exhaust gases that would otherwise pass unconverted through the catalyst during the cold start period. The EHC theoretical power required for a reference case (161) was 1600 watts to heat an EHC to 400°C in 15 s in order to initiate the catalytic reactions and obtain the resultant exotherm of the chemical energy contained in the exhaust. Demonstrations have been made of energy requirements of 15—20 Wh and 2 to 3 kW of power (160,161). Such systems have achieved nonmethane HC emissions below the California ULEV standard of 0.025 g/km. The principal issues of the EHC are system durabihty, battery life, system complexity, and cost (137,162—168). 

The TLEV, LEV, and ULEV standards incorporate the concept of reactivity-weighted mass emissions of VOC, concurrent with increasingly strict NOx control. The intent is to regulate based on equal ozone-forming potentials of the VOC emissions rather than simply on their total mass. That is, the emission standards for organics are set in terms of the amount of ozone formed in the atmosphere per mile traveled by a given vehicle/fuel combination rather than in terms of the simple total mass of VOC emitted per mile. 

These are 50,000-mi exhaust emission standards fleet average NMOG requirements begin at 0.25 g/mi in 1994 and are progressively reduced in subsequent years to a level of 0.062 g/mi. Any combination of TLEV, LEV, ULEV, ZEV, and 1993 conventional vehicles can be used. 

TLEV = transition low-emission vehicle LEV = low-emission vehicle ULEV = ultralow-emission vehicle. 

FFVs do leave room for improvement as General Motors demonstrated by optimizing a 3.1L Lumina to dedicated M85 operation. The engine compression ratio was increased from 8.9 (used in the FFV version) to 11.0. This was obtained by use of a smaller piston bowl, reduced crevice volume, etc. A close-coupled 80-cu.-in. palladium catalyst was added to the 170-cu.-in. palladium/ rhodium one. Performance results as compared to the FFV predecessor are shown in Table 1-1 [1.17]. Not only was performance increased, but fuel economy was increased while emissions were decreased. This vehicle was even then very close to meeting the California ULEV emissions standards. 

Dedicated Emissions (50,000 mile) in comparison to TLEV LEV ULEV... 

Dodge, L.G., et al., Development of a Dedicated Ethanol Ultra-Low Emission Vehicle (ULEV)—Phase 3 Report, National Renewable Energy Laboratory, Golden, Co., September 1996. 

ULEV Ultra Low Emission Vehicle—the most-stringent California vehicle emission standard for combustion vehicles. 

The five categories of California Low-Emission Vehicle Program standards, from least to most stringent, are TLEV, LEV, ULEV, SULEV and ZEV. 

Williams, J.L., Patil, M.D. and Hertl, W., By-Pass Hydrocarbon Adsorber System for ULEV, SAE, paper No. 960343 (1996). 

It is clear from this discussion that honeycomb substrates offer the unique advantage of design flexibility to meet the ever-changing performance and durability requirements. Since these requirements can often be conflicting, certain trade-offs in geometnc properties may be necessary, as illustrated in Table 1. New advances in honeycomb substrates, in terms of both ceramic composition and cell geometry, necessitated by more stringent performance and durability requirements for 1995-1- vehicles [equivalent to low-emission vehicle (LEV) and ultralow-emission vehicle (ULEV) standards] are summarized in Table... 

From Table 2 it is seen that ultra-low-emission vehicles (ULEV) will have to meet 0.04 g nonmethane hydrocarbons per mile traveled compared to 0.25 g per mile in 1993. In contrast, the CO and NOx emissions will only halve between 1993 and ULEV standards. While this does not mean that the CO and NOx standards are easily achievable, it highlights the greater importance attnbuted to the control of HC by the regulatory bodies in the United States. Similarly, the European standards for hydrocarbons are promulgated to reduce progressively at each stage of the legislation. In addition, for the first time the... 

An illustrative example is shown in Fig. 12 which shows the current-potential curve obtained during electrolysis of a dilute (0.01 M) solution of KI in H2SO4 using two Pt electrodes. The minimum potential, Ulev, required for the electrolysis reaction is 0.49 V, computed from thermodynamics via t/rev = —A G/nF,... 

The CNG vehicles were a technical success and included the first vehicles certified to the strict California low emissions vehicle (LEV) and ultra low emissions vehicle (ULEV) standards. They were also certified to the inherently low emissions vehicle (ILEV) category, and the full-sized van was certified to the California super ultra low emissions vehicle (SULEV) standard. 

TLEV transitional low emission vehicle LEV low emission vehicle ULEV ultralow emission vehicle ZEV zero emission vehicle. 

EHCs are a small catalyst installed ahead of the main catalyst. The substrate, onto which the active catalyst material is deposited, is made from metal so that when an electric current is passed it will heat up quickly. This brings the catalyst to its full operating temperature in a few seconds. Early electrically heated catalyst systems required high levels of power input but development of the systems has improved efficiencies so that the power requirement has been reduced to a tenth. EHC systems are currently available that have been demonstrated to meet Californian ULEV standards using 1-2 kW of additional power and 6-10 watt-hours energy consumption during the start-up phase. 

Using only a fresh main catalyst the cold-start emissions of hydrocarbons are about three times higher compared to the future legal requirements (ULEV). With decreasing catalyst activity the cold-start behavior of the main catalyst gets worse which results in increasing HC-emissions. 

Future legal requirements can be fulfilled with the EHC-concept for fresh catalysts. As the main catalyst is only heated by the exhaust gas again a considerable increase of the cold-start emissions results from catalytic aging. Hence, the ULEV-limit can not be kept for lower activities than 40 %. 

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