R&D on New-Generation Gasoline Fuel Technology for Improving the Environment

Transcription

1 2000M4.1.1 R&D on New-Generation Gasoline Fuel Technology for Improving the Environment (New Generation Gasoline Group) Masanori Hirose, Seitaro Yagi, Yasuhiro Kotani, Takashi Yoshizawa, Shigeo Senbokuya, Koichi Doya, Keiichi Koseki, Nobuyuki Takahashi, Noriyuki Tsuchiya, Tsutomu Uchiyama, Shigeru Suzuki, Kazuyoshi Yamamoto, Seiji Oizumi, Masashi Oikawa, Hideo Takesue, Kenji Morita, Michio Kojima, Tatsuji Matsumoto, Kenji Anzai, Masanobu Kawamura, Teruo Suzuki, Daisuke Takahashi, Tomonori Takada, Eisaku Sato, Toshima Nishioka, Toshihiko Suetomi, Takeshi Murayama, Masahiko Sako, Tetsuo Sanda, Shogo Suzuki 1. Introduction 1.1 Outline As concern about improving the atmospheric environment and about preventing global warming escalates worldwide, demand has arisen for significantly greater reduction of both fuel evaporative and exhaust emissions from automobiles, which are one of the major causes of these concerns. In Japan, the state of air pollution, comprised of nitrogen dioxide (NO 2 ), suspended particulate matter (SPM), photochemical oxidants, etc., remains critical, and in comparison to the 1978 regulations on emissions now enforced, the limits will be reduced by about one-third for gasoline vehicles on nitrogen oxides (NO X ), hydrocarbons (HC) and carbon monoxide (CO) from the year In addition, respecting fuel evaporative emissions, it has been decided that testing methods will be changed, that diurnal breathing loss (DBL) will be newly added to the conventional hot soak loss (HSL) and that regulations will be stringent substantially. Meanwhile, as a global warming countermeasure, the following reduction targets were adopted at the COP3 (The Third Conference of Parties to the UN Convention on Climate Change) for the year 2010 as percentages of warming gases in the year 1990: Japan, 6%; USA, 7%, and EU (European Union), 8%. In Japan, an average improvement of 22.8% in automobile fuel consumption, as compared to the year 1995, has been set for the year

2 Amid such demands for both low fuel consumption and low emissions, substantial efforts are being made to stimulate the spread of the direct-injection gasoline vehicle, one of the typical countermeasure technologies. In addition, many noteworthy technologies have appeared as countermeasures for reducing emissions. Examples include early catalyst light off technology, which acts as a cold mode countermeasure; catalyst poisoning reduction technology, which acts as a hot mode of emissions reduction and a means of catalyst durability; and studies of effective reduction through a combination of catalysts. As advances are made in technology for low fuel consumption and low emissions, in the present R&D, gasoline suitable for automobile technology from now into the future will be investigated from the standpoint of improvement in the atmospheric environment and practical performance and fuel consumption. Among atmospheric pollutants in Japan, attention has focused especially on the reduction of photochemical oxidant (ozone), NO X and SPM. Especially problematic are hydrocarbons, which contribute to the reactions that generate NO X and oxidants, exhaust substances associated with gasoline and gasoline vehicles in particular. Attention continues to focus on the generation of fuel evaporative emissions, which are the source of hydrocarbons. In 1999, vehicles equipped with the latest emissions reduction technologies were supplied for testing. With these vehicles, which had been marketed both in Japan and overseas, the exhaust behavior of fuel evaporative emissions from vehicles was investigated together with the possibilities for reducing the refueling emissions and the effects of the curtailment technology. The impact of sulfur in gasoline on exhaust emissions, centering on lean NO X catalyst, was also investigated. 2. Experimental and Results 2.1 Investigation of evaporative emissions Outline Curtailment of the hydrocarbons emissions from gasoline vehicles has been targeted in order to reduce photochemical oxidants, and as the levels of exhaust emissions reduces, the fuel evaporative emissions have been focused. Accordingly, Sealed Housing for Evaporative Determination (SHED) equipment was used to investigate gasoline vapor pressure (Reid Vapor Pressure: RVP) and the impact of countermeasures for reducing fuel evaporative emissions from vehicles on the emissions levels Test method Regular gasolines with RVP of 55 kpa to 75 kpa were used as test fuels. The domestic, new fuel evaporative emissions testing method, applicable to emissions regulations in the year 2000, was used for HSL and DBL, and because running loss (RL) was not incorporated into year 2000 emissions regulations, the evaluation method was made to comply with the testing method used in the Japan Clean Air Program (JCAP). The test method is shown in Table

3 Table Comparison of fuel evaporative emissions test methods (test conditions) RL Compliance with JCAP method Conditions LA-4,NYCC,LA-4 (73 minutes) 11 mode mode 3 times Method SHED method * SHED method Ambient temperature 35 C 41 C 35 C Fuel tank temperature Measured fuel temperature profile in running mode Measured fuel temperature profile in running mode Standard 0.05 g/mile - HSL Compliance with Year 2000 standard method Measurement time After RL measurement After 40 km/h 40 minutes After 11 mode mode 3 times Method SHED method * Carbon canister trap method SHED method Enclosure method (SHED method) Period 1 hour 1 hour 1 hour Ambient temperature 35 C 41 C 25 C 27 C Standard 2.0 g/test (total of DBL and HSL) 2.0 g/test DBL Compliance with Year 2000 standard method Measurement time 6 to 36 hours after HSL measurement 6 to 36 hours after HSL measurement Method SHED method * SHED method Period 24 hours 3 times 24 hours Ambient temperature 22/36 C 18/41 C 20/35 C Standard highest value of 3 times 2.0 g/test with HSL+DBL Test vehicles *Note: Point source method also possible. The test vehicles consisted of one vehicle made in Japan where the technology for curtailment of fuel evaporative emissions is different (no countermeasure yet for evaporative emissions); one vehicle with improved evaporative emissions, made in Japan and conforming to year 2000 emissions regulations; and one vehicle made in the USA (1996 model conforming to US federal regulations on evaporative emissions). Specifications of the test vehicles are listed in Table

4 Table Various specifications of test vehicles (fuel evaporative emissions) Vehicle A Vehicle B Vehicle C Model year Displacement (L) No. of cylinders 4 V6 V6 Fuel supply system MPI MPI MPI Installation of fuel tank Under floor In trank Under floor Fuel tank capacity (L) Canister capacity (L) Remarks Made in Japan. Vehicle complies with 1978 standard Made in Japan. Vehicle complies with 2000 standard LEV vehicle of California, USA Impact of RVP and vehicle countermeasure technology on fuel evaporative emissions The relationship between RL and RVP is shown in Figure In a current vehicle produced domestically (vehicle A: conforms to 1978 regulations), when RVP exceeded 65 kpa, the RL increased sharply together with a rise in RVP. However, the RL of the domestically produced vehicle B, which conforms to 2000 regulations, and of the vehicle C of the USA exhibited remarkably low values, and almost no dependency on RVP could be noted. Because the vehicle C complies with US federal regulations in 1996, including RL regulations, it is believed that RL was curtailed forcibly as a result of countermeasures taken, such as increase of the canister cubic capacity or strengthening of the canister purge. In terms of canister cubic capacity, the B vehicle, which complies with 2000 regulations, is 1/3 or less than the vehicle C, and it is surmised that an RL level comparable to that of vehicles subjected to US countermeasures was realized as a result of countermeasures taken, primarily adequate implementation of canister purging. Figure RL displacement volume versus RVP 4

5 Figure HSL + DBL versus RVP Figure present the relationship between RVP and the total of HSL and DBL. In the vehicle A, as with RL, when the test fuel RVP exceeds 65 kpa, a tendency for the levels to increase together with an increase in RVP could be noted, but up to 65 kpa, the levels stayed below 2.0 g/test, which is the regulation value for HSL + DBL in Japan s new fuel evaporative emissions test method (the RVP designated at 56 to 60 kpa). On the other hand, the HSL + DBL of the domestically produced vehicle B, which conforms to 2000 regulations, and of the vehicle C produced in the USA, were about 1/2 or less that of the domestic vehicle currently being produced, and almost no dependency on RVP could be noted. Even with fuel with 72 kpa, the upper limit of voluntary regulations on RVP in gasoline to be commercialized from the summer of 2001, it became evident that HSL + DBL would be well below 2.0 g/test. 2.2 Investigation of refueling emissions Outline In the USA, federal regulations on refueling emissions were introduced from 1998, and a recovery system (ORVR: On Board Refueling Vapor Recovery) began to be mounted on vehicles. Accordingly, a study was done on the impact of RVP on refueling emissions, using both vehicles equipped with and without ORVR Test method Two types of gasoline, 60 kpa and 70 kpa, were used as test fuels. The 60 kpa fuel is the EPA standard test fuel, and the 70 kpa fuel is equivalent to the regular gasoline on the market in Japan on average in the summer. Because chassis equipment is required for 40 CFR , and , the approval test methods (FTP) in the USA, the ATRI method, which does not require chassis equipment with FTP as reference but yields results equivalent to FTP, was established as the evaluation method. The ATRI method is represented in Figure

6 Refuel/Drain Preconditioning (canister) Drain test fuel and fill tank to 40% capacity. After purging canister with air, load with butane/nitrogen and saturate active coal. Refuel Fill to 95% of tank capacity. Preconditioning (vehicle) Idling (3000 rpm 30 minutes) Disconnect canister from fuel tank. Refuel/Drain Vehicle soak Drain test fuel and fill tank to 10% capacity. Perform at enclosure (26.7 C, 6 to 24 hours) Connect canister and fuel tank. Refuel test Fill to 95% of tank capacity. Figure Evaluation test of evaporative emissions during refueling (ATRI method) Test vehicles The test vehicles are indicated in Table The vehicle D is a domestically produced vehicle that complies with 1978 emissions regulations. The vehicle E and vehicle F are both vehicles of the same name by the same maker in the USA, but the vehicle F is equipped with an ORVR unit and the vehicle E is not. Table Specifications of test vehicles (evaporative emissions during refueling) Vehicle D Vehicle E Vehicle F Model year Displacement (L) No. of cylinders 4 V6 V6 Fuel supply system MPI MPI MPI Fuel tank capacity (L) Canister position Engine room Under floor Under floor Canister capacity (L) ORVR No No Yes Standard 1978 TLEV of California LEV of California 6

7 2.2.4 Impact of RVP and vehicle countermeasure technology on refueling emissions Figure shows a comparison of refueling emissions, depending on the presence or absence of ORVR unit in the same type of vehicle by the same OEM. In the figure, the dotted line denotes the regulation value for refueling emissions that was phased in by the US federal government in From a comparison of the vehicle F, which has an ORVR unit, with the vehicle E, which does not have an ORVR unit, it was found that the refueling emissions are curtailed forcibly to 1 to 2%. What is more, the absolute value of emissions levels is 20 to 30% of the US federal regulation value in an ORVR equipped vehicle; it is about 20 times greater in vehicles without ORVR unit. Evaporative emissions during refueling (g/gal.) 60 kpa 70 kpa Reduction to 1/50 to 1/100 By ORVR EPA Standard = 0.2 g/gal. (60 kpa) Vehicle F (with ORVR) Vehicle E (with ORVR) Figure Comparison of evaporative emissions during refueling with and without ORVR Figure presents the results of an investigation of the impact of RVP on refueling emissions in the vehicle E of the USA and in the vehicle D, produced in Japan without ORVR unit. In the figure, the CRC estimated value is the result of calculation after the conditions of the experiment were input to the CRC formula for estimating evaporative emissions volume during oil supply. The CRC estimation formula is given below. Evaporative emissions (g/gal.) = exp ( T TD RVP) Where T: TD: Differential between fuel tank temperature and refueling fuel temperature ( F) Supply oil fuel temperature ( F) RVP: RVP for refueling fuel (psi) 7

8 Evaporative emissions during refueling (g/gal.) Figure % width Vehicle D Vehicle E CRC estimate Influence of RVP on fuel evaporative emissions during refueling (without ORVR) The figure shows that the refueling emissions in the vehicle E of the USA is at the same level as in the vehicle D produced in Japan without ORVR unit and the emissions levels were reduced by a drop in gasoline vaporization pressure; by lowering RVP from 70 kpa to 60 kpa, the emissions volume was reduced to 85 to 88%. The emissions volumes from the two vehicles also matched well with the CRC estimated value. From the results of Figure and Figure 2.2-3, it became clear that although a drop in RVP is effective in terms of reducing refueling emissions, the effect of mounting an ORVR unit is much greater. 2.3 Investigation of the impact of sulfur in gasoline on exhaust emissions Outline Using the exhaust emissions test method of Japan (10.15 mode), an evaluation was made of the impact of sulfur concentration in gasoline on exhaust emissions (CO, THC, NO X ). In 1999, as the first step in determining the basic performance impact of lean NO X catalyst (selective reduction-type catalyst, NO X storage-type catalyst) and three way catalyst as a reference, on the concentration of sulfur in gasoline, catalyst was regenerated with each test and the impact of sulfur poisoning was investigated by the method of evaluation over the short term. In addition, new catalyst and used catalyst were analyzed in order to investigate the mechanism of catalyst deterioration by sulfur in gasoline Test method For the evaluation, a method was employed in which the mode test is repeated about 10 times after conducting sulfur removal operations, and regulated exhaust emissions (CO, THC, NO X ) levels were compared. In the sulfur removal operation, vehicle speed (overdrive OFF) was adjusted so that the catalyst outlet temperature becomes 630 or 650 C, and then either the 10-minute holding method or the regeneration method employed at JCAP was adopted. With NO X storage-type catalyst, the exhaust emissions were measured at a constant speed because the NO X conversion rate is poor after high-speed running. 8

9 2.3.3 Test fuels Test fuel properties are listed in Table and Table A sulfur-containing reagent was added to premium gasoline on the market, which was adjusted so that the concentration of sulfur covers within the range of 3 to 90 ppm, the same as the sulfur concentration in gasoline on the market. Table Test fuel properties (Exhaust emissions) F01 F02 Density (g/cm 3 ) Distillation 10% ( ) 50% % MTBE (vol%) Aromatics (vol%) Olefins (vol%) Table Sulfur contents in fuels Base F01 F02 Fuel 4 3 Test Fuels of Sulfur Series Benzene (vol%) Sulfur (ppm) 4 3 RON Test vehicles Specifications of test vehicles are given in Table Vehicle G is a three way catalyst mounted vehicle (Stoichio). Vehicle H is a lean-burn vehicle with NO X storage-type catalyst mounted. Vehicle I is a direct injection vehicle (model vehicle) mounted with a selective reduction-type catalyst which can meet new short-term regulations. Vehicle J is a direct injection vehicle with a three way catalyst directly under the engine for facilitating cold starting, and a new NO X storage-type catalyst under the floor. Table Specifications of test vehicles (exhaust emissions) Vehicle Displacement (L) Engine Type Catalyst Mileage (km) Model Year G 1.5 Stoichio TWC 12, H 1.8 Lean-burn NOx storage 7,000/30, I 1.8 Direct-injection NOx selective reduction 7, J 2.0 Direct-injection TWC+NOx storage 7,

10 2.3.5 Impact of gasoline sulfur on exhaust emissions The results for vehicle G (Stoichio, TWC) are given in Figure Within a sulfur concentration range of 3 to 80 ppm, when the sulfur concentration was increased, the emissions levels tended to increase slightly. Figure shows the results for vehicle H (lean-burn, NO X storage). Within a sulfur concentration range of 11 to 90 ppm, the emissions levels did not change. Figure shows the results for vehicle I (direct-injection, NO X selective reduction). Within a sulfur concentration range of 11 to 90 ppm, the volume of emissions did not change. This is ascribed to the fact that Ir is used in the catalyst. It was also learned that the volume of exhaust gas emissions is kept low. The results for vehicle J (direct-injection, NO X storage) are given in Figure In vehicle J the emissions volume is lower than in vehicle H, perhaps because it employs two types of catalyst, namely, three way catalyst and NO X storage catalyst (new type compared to vehicle H). When the sulfur concentration was increased, THC and NO X did not change, but CO increased slightly. From the results of the four vehicles, it was determined that the impact resulting from vehicle differences is greater than the impact of sulfur concentration on exhaust emissions NOx THC CO 0.60 NOx THC CO Exhaust emissions (g/km) Exhaust emissions (g/km) Fuel sulfur concentration (ppm) Fuel sulfur concentration (ppm) Figure Influence of sulfur concentration Vehicle G (Stoichio, TWC) Figure Influence of sulfur concentration Vehicle H (Lean-burn,Nox storage) 0.60 NOx THC CO 0.60 NOx THC CO Exhaust emissions (g/km) Exhaust emissions (g/km) Figure Fuel sulfur concentration (ppm) Influence of sulfur concentration) VehicleI(Direct-injection, Nox selective reduction) 0.00 Figure Fuel sulfur concentration (ppm) Influence of sulfur concentration Vehicle J (Direct-injection, TWC + Nox, storage) 10

11 Next, the impact of the regeneration method was investigated. With vehicle J, evaluation was made by the JCAP method and by the method of regeneration in 10 minutes at 630 C. The results are shown in Figures and The results indicated that the pattern of exhaust emissions varies greatly by regeneration method NOx THC CO 0.60 NOx THC CO Exhaust emissions (g/km) Exhaust emissions (g/km) Fuel sulfur concentration (ppm) Fuel sulfur concentration (ppm) Figure Regeneration by JCAP method (vehicle J) Figure minute regeneration at 630 C (vehicle J) In order to investigate the mechanism of catalyst deterioration due to sulfur in gasoline, new catalyst and used catalyst were analyzed. An example of the results is presented in Figure The figure illustrates the XRD pattern of NO X storage-type catalyst after a vehicle analogous to vehicle H has run 30,000 km. The results indicate that in the catalyst at upstream, BaSO 4 and BaAl 2 O 4 were generated and at downstream, BaSO 4 was generated. BaSO 4 was generated because Ba was poisoned by the sulfur. It is believed that BaAl 2 O 4 was generated as a result of sintering due to heat at the catalyst upstream. In addition, other significant information was obtained such as Ba, sulfur and precious metal contents, and surface analysis by EPMA (Electron Probe Micro Analyzer) and the degree of active metal dispersion from CO chemical adsorption. 600 cps BaSO4 ( ) CeO2 ( ) BaAl2O4 (17-306) 30,000 3 万 km 下流 km Cat. outlet θ/deg 図.1 コロナ触媒 (3 万 km) の XRD パターン 330,000 万 km 上流 km Cat. inlet cor30203.ctl CF0203.dat Figure Catalyst (NOx storage) XRD after running vehicle H for 30,000 km 11

12 3. Conclusions 3.1 Investigation of evaporative emissions from vehicles (1) From new fuel evaporative emissions test methods to be used in year 2000 emissions regulations, it was clarified that the HSL + DBL of current U.S. vehicles ranges from 1/2 to 1/20 that of vehicles produced in Japan. (2) Within the range up to RVP75 kpa, it was clarified that fuel RVP has almost no impact on the HSL+DBL of U.S. vehicles. (3) It was clarified that of the current U.S. vehicles, there are some that do not break down even when the DBL period is extended to 6 days. (4) The RL and HSL + DBL of vehicles matching year 2000 emissions regulations are at about the same level as current U.S. vehicles. (5) Using the same vehicle and fuel, the emissions volumes of HSL + DBL were compared by the test procedure for year 2000 emissions regulations in Japan, by the Supplemental Two Day Test in the USA and by the STEP III test method in Europe. In the Japanese and European tests, the emissions volumes were roughly equivalent, but under U.S. federal law, the emissions volume was 60% over the regulation value. 3.2 Investigation of refueling emissions (1) Using Japanese gasoline, it was found that evaporative emissions during oil supply can be effectively reduced 98 to 99% by ORVR countermeasure. (2) Although the drop in RVP was effective, the effect of the ORVR unit was much greater. (3) From overseas surveys, etc., it was learned that the cost of ORVR countermeasures, based on vehicles that match U.S. regulations on fuel evaporative emissions in 1996, is low at 6 to 8 US$/vehicle. 3.3 Investigation of the impact of gasoline sulfur on exhaust emissions (1) It was determined that the impact resulting from vehicle differences is greater than the impact of sulfur concentration on exhaust emissions. (2) It was clarified that air-fuel ratio control and operating conditions are vital factors affecting the level of exhaust emissions. (3) A system of continuous measurement of exhaust emissions pre- and post- catalyst was constructed, and its effectiveness was demonstrated. (4) Characterization of exhaust emissions conversion catalyst has become possible, and it was confirmed as being effective in elucidating the mechanism of change in catalyst activity. 12

13 4. Future Issues As regulations on emissions become stringent, in addition to development of direct injection gasoline vehicles, etc., aimed at both low fuel consumption and low emissions, as discussed earlier, many noteworthy technologies have appeared as countermeasures for reducing emissions. Examples include early catalyst light off technology, which acts as a cold mode countermeasure; catalyst poisoning reduction technology, which acts as a hot mode of emissions reduction and a means of prolonging catalyst durability; and studies of effective reduction through a combination of catalysts. At the same time, as shown in WWFC, etc., demands for fuel quality have become much stricter. Accordingly, evaluation of vehicles with advanced emissions reduction countermeasures, determination of the impact levels of fuel properties, and reflection of such findings in the qualitative design of fuel have all become crucial. In these conditions, the following items will be investigated in future. (1) Confirmation of the evaporative emissions reduction effect of each elemental technology (strengthening of canister purge, other) by special units for evaluating evaporative emissions generation, etc. (2) Investigation of the impact of fuel properties on ozone generation potential (both evaporative emissions and exhaust emissions) (3) Fact-finding study of evaporative emissions during refueling; confirmation of the effects of evaporative emissions reduction technology (stage II) during refueling at SS; and comparison with effects of ORVR (4) Confirmation of the impact of fuel sulfur on exhaust emissions in the latest direct-injection vehicles (5) Confirmation of the impact of fuel sulfur on exhaust emissions in the latest direct-injection vehicles after long-distance running. (6) Confirmation of the impact of air-fuel ratio on the performance of lean NO X catalyst. (7) Elucidation of the mechanism of catalyst performance through the characterization of exhaust emissions conversion. Copyright 2000 Petroleum Energy Center all rights reserved.