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Report by the Committee on Motor Vehicle Emissions (1973)
Board on Environmental Studies and Toxicology (BEST)

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3. POTENTIAL OF SPARK-IGNITION INTERNAL-COMBUSTION ENGINES PASSING EMISSION CERTIFICATION FOR 1975 and 1976 3. 1 Introduction The invests gations of the Committee to date have shown that, according to current planning of the automobile manufacturers, the great majority of the engines to be used in 1975-76 model year vehi- cles will be conventional, reciprocate ng, spark-ignition engines . A smaller fraction of the 1975-76 vehicles will use Wankel rotary engines, and one manufacturer (Honda) has plans to produce a new type of carbu- reted stratified-charge engine. Some passenger-car diesel engines will still be produced, but these will differ only slightly from the diesel engines currently available. Diesel engines are discussed more fully in Section 6.1. This section of the report will present an analysis and evalua- tion of the prospects of spark-ignition engines passing the emissions certification test for 1975 and 1976 model year vehicles. 3 2 Current Status of 1975 Systems . The January 1, 1972, report of the CMVE dealt at considerable length with the technological feasibility of meeting the 1975 standards. At the present time, most automobile manufacturers have developed s~me- what similar prototype emission-control systems for their 1975 model year vehicles. The major U. S. and foreign manufacturers are currently assembling and testing fleets of vehicles equipped with the complete system to evaluate different promising catalyst materials and to obtain data on system durability before final production designs are frozen. These 1975 emission-control systems typically consist of: (i) An improved carburetor to provide more accurate fuel metering, with compensation for air-density changes, and with an —22 -

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electrically powered choke that comes off quickly at ambient temperatures of about 70 F. (ii) A quick-heat intake manifold designed to promote rapid fuel evaporation after engine start-up. (ii;) An electronic ignition system to eliminate the wear and other problems of current distributor assemblies and to allow easier spark-t~ming control. (Inadequate maintenance of present distributors commonly results in increased engine emissions.) (iv) An exhaust-gas recycle (EGR) line and control valve de- signed to recycle about 10 percent of the exhaust flow to hold NOx emissions below 3 grams per mile (g/mile). (v) An air pomp to inject air into the exhaust ports to oxidize carbon monoxide and hydrocarbons. (vi) A catalytic converter in the exhaust system to promote further oxidation of the HC and CO emissions from the engine. For same manufacturers, the current fleet tests represent the first extensive evaluation of the complete engine emission controls with the best oxidation catalyst materials now available. Data ob- tained fray same of these manufacturers' fleets are shown in Table 3-1. Most of the data in Section 3 of this report were received in reply to a questionnaire dated July 13, 1972 or were presented during recent panel visits.) These tests follow the durability driving cycle and maintenance procedures used in the emissions certification of vehicles. Progress in emission control for 1975 systems using catalytic converters has been made since the CM7E report of January 1, 1972. It is highly probable that most manufacturers will be able to produce vehicles that will pass the 1975 certification test procedure, providing - 23 -

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allowance is made for one catalyst replacement during the 50,000-mile durability tests, that fuel containing suffice entry low levels of lead and other catalyst poisons is used, and that averaging of emissions within automobile and engine classes is allowed. Emission-control systems are also being developed that do not use catalysts and therefore have improved durability over the catalytic systems. The three-valve strat~fied-charge carbureted engine, under development by Honda, has achieved emissions below the 1975 standards at low mileage on compact cars (for details, see Section 3.9.23. Three vehicles equipped with a 2-l~ter engine (122 CID) have completed 50,000- mile durability testing and met the standards at every test throughout the test period. The Wankel engine with a thermal reactor has achieved emission levels below the 1975 standards in a compact car. This system has already demonstrated improved durability over a catalytic system. Data from the few cars tested over extended mileage indicate that deteriora- tion will be relatively low. 3.3 Engine Emissions for 1976 Systems 3.3.1 Introduction In developing systems to meet the 1975 standards, most automo- bile manufacturers have emphasized that such systems must be compatible with 1976 requirements. There has thus been a concentration on 1975 control systems that can be modified to achieve the greater NO emission control called for in 1976 Additional NO control can be achieved by increasing the amount of exhaust-gas recycle, by adding an NO -reducing catalytic converter to the exhaust system, or by a combination of both techniques. -25-

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To approach the 0.4 g/mile NOx level with a conventional spark- ignit~on engine, a combination of both techniques appears to be required. The use of large amounts of EGR (20 percent or more) results in a large fuel-economy penalty, severe driveability problems with attendant safety hazards, and an increase in engine HO and CO emissions. It is not prac- tical at this stage to achieve NO -emission levels approaching 0.4 g/mile with EGR alone in a conventional engine. Without EGR, engine NOR emissions vary between about 3 and 8 g/ mile' depending on the air-fuel ratio' spark timing' engine size' and other details of engine design and operation. In the dual-catalyst sys- tem, a separate NOx-reduction catalyst is added to the exhaust system, between the engine and the oxidation catalyst. In the three-way catalyst system, a single catalytic converter simultaneously reduces the concen- tration of all three pollutants (HC, CO, and NOx) in the exhaust stream. Air-fuel ratio must be closely regulated in such systems. The NO - reduction catalysts currently available, as will be described below, are not able to retain sufficient activity over extended mileage to reduce these engine emissions below the 1976 standards. Thus, unless further Improvements in NOx catalyst durability occur over the next year, only systems for conventional engines with increased EGR and an NO -reduc- tion catalyst show any promise of approaching the 0.4 Simile level. To minimize demands on catalyst size, cost, and durability, there is a continuing emphasis on achieving low and stable engine emissions. Tech- niques for controlling emissions during the first part of the test when the engine is still cold, fuel-metering requirements, EGR systems, and the potential for improved engine emissions control are examined next. 3 3.2 Cold-Start Emission Controls . With 1975-76 catalyst-based emission-control systems, a large portion of the carbon monoxide and hydrocarbon emissions occur during the cold-start and engine warm-up phase of the drive schedule in the CVS-CH test. To compensate for the low volatility of cold gasoline, a - 26 -

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rich mixture must be provided during cold starts. The excess fuel is not fully burned in the combustion chamber, and the cold engine thus emits high levels of hydrocarbons and carbon monoxide. Because the oxidizing catalyst is inefficient while cold, large amounts of these contaminants are discharged to the atmosphere. Although the NO cata- lyst is also cold and ineffective during start-up, cold-start NO emis- sions tend to be lower because rich mixtures and cold cylinder walls reduce the formation of NO . x Because of the high HO and CO emissions during the cold start, considerable development effort has been spent in a number of cold-start controls and procedures. In the prototypes of their 1975 and 1976 sys- tems, most manufacturers have elected to modify the cold-start process. Specifically, they have achieved start-up with leaner air-fuel mixtures by preheating the air and fuel, by improving the mixture control in the carburetor, and by shortening the choking period without seriously im- pairing cold engine operation and driveability. Most prototypes ~ nclude air and fuel preheat systems arid modified choke operation. The purpose of preheating air and fuel is to achieve higher volatility with cold fuel, which, in tulle, allows leaner engine opera- tion and shorter choking period during warm-up. The air preheat system that has been incorporated in most 1970 and subsequent American-make cars, and has proven reliable, will be used in most 1975-76 models. In addition to heating the intake air, several proposed emission- control systems promote further evaporation of the fuel by supplying heat to the base of the carburetor. This is accomplished by using a heat exchanger between the carburetor and the exhaust-manifold crossover, causing the fuel droplets to make contact with a hot surface and to flash into vapor. Several problems remain to be solved to ensure that production units can attain the emission reduction predicted by exper~- mental designs. While durability of the system has not yet been evalu- ated, there appear to be no major technical difficulties.

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A quick-acting choke, employing electrical or mechanical timing devices, will be used to lean out the mixture as early as possible after start-up. For sys t ems incorporating air and mixture preheating, choking times have been reduced from several minutes to less than 30 seconds, while maintaining adequate driveabi lity. 3.3.3 Carburetors The precise metering of the fuel and air to automotive engines has become much more important in recent years because the mixture ratio is a critical parameter affecting the exhaust composition and the func- tioning of exhaust-treating devices. Most 1975-76 model carburetors have been redesigned to achieve better air-fuel ratio control and main- tain good co Id - s tart pert ormance o f the engine . Except for the demands during extreme accelerations and decelera- tions, the newly designed carburetors are capable of maintaining toler- ances of ~ 3 percent of the set air-fuel ratio. This approaches the fuel-metering accuracy required for the dual-catalyst 1976 control systems in which the air-fuel ratio must be held between about 13.8 and 14.5 to achieve adequate NOx reduction in the first catalytic converter. Considerable design work remains to be done to ensure durability with these finely adjusted carburetors. Most manufacturers are consid- er~ng factory-sealed, t~mper-proof settings because it is believed ~m- possible for a typical mechanic to make the required adjustments. The dependability of these factory-set adjustments is unknown. 3.3.4 Electronic Fuel Inj ection Several companies are considering Electronic Fuel Injection (EFI) as an alternative to the carburetor. In such systems, an elec- tronic module controls the amount of fuel provided to the engine. - 28 -

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- An advantage of electronic control is that, by using appropriate transducers, air-fuel ratio can be compensated for variations in such operating parameters as engine speed, manifold vacuum, ambient condi- tions, various engine temperatures, exhaust composition, etc. Thus, there is potential for adequate control of mixture ratio over a wide range of operating conditions. EFI systems can respond quickly to changes in operating conditions and are therefore able to provide sat- isfactory control of air-fuel ratio under transient conditions. However, contacts made with carburetor manufacturers, automobile manufacturers, and producers of electronic fuel injection equipment indicate that cur- rent EFI systems do not provide substantial improvement in air-fuel con- trol over the advanced-design carburetors operated under steady condi- tions. EFI systems have been and are in production on several European cars. Field experience with these systems initially showed a high com- ponent-failure rate, although performance is improving. The advantage of EFI over current carburetors in small cars is in performance charac- teristics and fuel economy, i.e., Increased power output, particularly for high-rpm high-performance engines Better fuel economy for high-speed driving Improved driveability, particularly with manual shift engines At least one manufacturer is introducing a mechanically con- trolled fuel-injection system which may show performance comparable with the improved EFI system and at savings in cost. 3.3.5 Exhaust-Gas Recycle (EGR) The most extensively developed technique for reducing engine NOx emissions is the recycling of a fraction of the exhaust to the - 29 - i

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engine intake. The recycled exhaust gases dilute the fresh mixture, thus reducing peak combustion temperatures and NOx-formation rates. The disadvantages of EGR are the loss in engine power and the reduction in tolerable air-fuel ratio variations consistent with smooth engine opera- tion. The use of EGR requires sorae mixture enrichment to maintain adequate driveability, which results in a fuel-economy penalty. In most systems, EGR is cut out at wide-open throttle and idle operation. EGR was introduced in most 1973 model year vehicles to bring NO below 3 gamble. Experience from the durability testing of these EGE systems indicates that plugging of the recycle line and control valve with leaded fuels is a significant problem. But with unleaded fuels, and with regular inspection and cleaning of the system, these problems are not expected to be severe. x As the amount of EGR is increased to reduce NO engine emissions below 3 g/mile, there is a need for more precise matching of the recycle flow to fresh mixture flow, and for more uniform mixing of the recycled exhaust in the intake. Engine cambustion-chember redesign with higher turbulence levels to promote more rapid combustion also improves the tolerance of the engines to EGR. 3 . 3 . 6 Potential for Engine Emis sion Reduction The methods of emission reduction discussed so far have been engine modifications that reduce emissions from the bare engine, i.e., before after-trea~ment devices such as catalysts and thermal reactors. The first two rows of Table 3-2 give typical engine emissions from a General Motors Corporation 1972 production audit. Both mean emissions and the standard deviation are given. The magnitude of the standard deviation indicates the spread in emissions about the mean value. This spread is due to differences in items such as brake setting, variations in transmissions, engine friction, carburetor settings, and stacking up - 30 -

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TABLE 3-2 Engine Emissions at Low Mileage: Mean and Standard Deviation Emissions in grams/mile( ) - CO mean (S.D.) mean (S.D.) NO mean (S.D.) GM 1972 production (b) (c) audit 1.7 (0.64) 22 (8.3) ~ 4 (.~1) Bes t GM divis ion 1972 production 1.2 (0.32) 16 (6.2) ~ 4 (~1~(C) Potential ( ~ best engine emissions, lean carburetion 1 (0.15) 10 (3) 2eS Potential best (e) engine emissions, rich carburetion 1.5 25 1.5 ( ) 1972 C7S-C test procedure (b ) 3656 vehicles tes ted ~ California 7-mode test emissions multiplied by 2 (c)Standard-size engine, standard-size car, with quick heat manifold, improved carburetor' quick acting choke, and EGR (c)Same as (d) and with air injection into the exhaust manifold - 31 -

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of engine tolerances. The best Gil division has been able to reduce both mean engirdle Omissions and the spread in emissions through improved production control, as indicated in the second row of the table. With the addition of a quick-heat manifold and an improved car- buretor with a quick-acting choke, these HC and CO engine emissions can be improved. However, use of EGR to reduce NO emissions requires some mixture enrichment to compensate for the decreased flame speed, and engine HC and CO emissions rise. The last Two rows in Table 3-2 are estimates of achievable engine emissions goals at low mileage for stan- dard-size engined in standard-size vehicles. The third row corresponds to a lean and the fourth row to a richer carburetor Betty ng. The fur- ther reduction of emissions in conventional engines must be achieved with exhaust treatment, such as catalysts or thermal reactors . 3.4 Catalysts The control system for 1976 on which most development effort has been concentrated uses two catalyst beds to clean up the engine emissions before exhaust to the atmosphere. A typical system layout is shown in Figure 3-1. The bed closest to the engine is used to remove NO . It is operated under net reducing exhaust-gas conditions (between 1 and 2 percent carbon monoxide in the exhaust gas, correspond- ing to a slightly rich carburetor calibration). Air is then added to the exhaust stream between the catalyst beds, and the remaining XC and CO emissions are removed in the second catalyst, the oxidation bed. The two catalytic beds may be in separate containers as shown in the figure, or they may be packaged in a single container. The system is a logical development of the 1975 control system described previously. Because the NO catalyst bed must be placed ahead of the oxida- tion bed, the oxidation catalyst warms up more slowly. Control of HC and CO emis signs during start-up would thus be delayed if air were always injected between the catalyst beds. To maintain control over - 32 - .

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The fuel-rich mixture ensures good ignition; the approximately stoichiometric mixture at the prechember exit propagates the flame into the fuel-lean mixture in the main chamber. A slow-burning flame is required to reduce NOX formation and allow HC and CO burnup inside the engine. Emissions of NOx, CO, and HC are all lower than those of a con- ventional engine at the same lean air-fuel ratios. In February 1971, emissions data with this system on engine dynamometer tests indicated the engine could meet 1975 standards; the first successful car test that met the standards was in Spring 1972. In addition to developing a 2-liter, 4-cylinder engine for their own vehicle, Honda has applied the same techniques to modify two Chevrolet Vega 4-cylinder engines. The Honda system is the most developed stratified-charge engine to date and has the lowest bare-engine emissions. Low-mileage emissions data are given in Table 3-11 for 54 Honda vehicles and two modified GM Vegas. All these cars met the 1975 standards without EGR or exhaust treatment, and Honda has expressed confidence that larger engines using the CVCC approach could also be made to meet 1975 standards without a catalyst. Especially impressive is the standard deviation of the low- mileage emissions of these vehicles. The standard deviation is 10 to 15 percent of the mean emissions. In comparison, mass-produced con- ventional-engine vehicles show standard deviations of 30 percent of the mean at higher emission levels. Three Honda cars have completed 50,000-mile durability test- ing and met the 1975 standards with ease at every 4,000 miles. Data for these tests are given in Table 3-12. The Federal Test Procedure 11-lap mode was followed in these tests. Maintenance required was minor. In a recent series of three tests at low mileage, the average emissions measured were 0.25 grams per mile HC, 2.5 grams per mile CO, - 59 -

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and 0.43 grams per mile NOX. These levels were achieved by improving the configuration of the auxiliary combustion chamber and the air-fuel control pattern. No EGR or exhaust-treatment devices were used. The emissions are not especially sensitive to variations in air- fuel ratio, Thus the required performance of the double carburetor sys- t~m is no more demanding than current requirements. The two throttle plates are linked mechanically. The mean air-fuel ratio varies with operating mode. The new cylinder head is about the same height as a conventional head. The new head, intake, and carburetor on the modified Vega fit comfortably into the end ne compartment. The engine can operate on regular leaded gasoline; durability testing has been on unleaded gaso- line to simulate fuel anticipated in the United States in 1975. The effects on vehicle performance of the CVCC system are small. There is a s light loss in power for the same engine displacement due to leaner operation and decreased volumetric efficiency. Fuel economy is essentially unchanged. There are no driveability penalties. Development of the Honda CVCC engine to achieve lower NO emis- sions is continuing. The effects of EGR and modifications to the basic combust~ on process are being examined. 3.10 Effect of Emission-Control Devices on Vehicle Performance, Driveability, Fuel Economy, and Safety Some of the emission-control devices and techniques required to meet the 1976 emission standards have a profound effect on at least three areas of vehicle performance: acceleration capability, fuel economy, and driveability. There is also some concern that poor per- formance of such cars will make them unsafe in certain circumstances, for example, if the vehicle stalls when accelerating into fast-moving - 62 -

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traf fic . The customer is sensitive to these characteristics which affect both his pocketbook and his attitude toward any particular vehicle. Traditionally this area has been one in which customer complaints and warranty returns have been especially prevalent. It is therefore not surprising that manufacturers have registered great con- cern in the past about the adverse effects of emission control devices. By the some token, however, the market place imposes considerable in- herent motivation for manufacturers to devote great attention to pro- duct improvement in these areas. The continents that follow in this section refer primarily to vehicles equipped with the dual-catalyst emission-control system. In general, vehicle acceleration capability is reduced by control measures applied for control of all three pollutants (HC, CO, and NOx); however, NO control measures which reduce combustion tem- perature have the most serious deleterious effects. Reductions in compression ratio to enable use of l~wer-octane gasoline resulted in acceleration penalties, as did the minimization of enrichment tech- niques formerly provided specifi cally for rapid acceleration capabil- ity. In addition, the use of EGR to reduce combustion temperatures and thereby inhibit NOx production imposes a severe acceleration penalty. Losses in fuel economy accompany most of these losses in ac- celerat~on capability and are aggravated by countermeasures taken to overcome deficiencies in acceleration capability and driveability. Many of the smaller engines have been dropped in the various car lines. The use of a larger displacement engine results in a fuel economy pen- alty for both city and open-h~ghway driving. When EGR is used to con- trol NOx emissions, the mixture must be enriched to retain adequate driveab;lity , causing drastic reductions in fuel economy . - 63 -

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The most troublesome of numerous driveab:ility problems is the cold-start problem, The quick choke action and subsequent lean mixtures required to minimize HO and CO emissions introduce problems with engine stalls and unsatisfactory drive-away during warm-up. EGR and spark retard cause such problems as lack of response, die-outs, and hesitation on acceleration. In its January 1, 1972, report, the COVE concluded that all three areas of vehicle performance discussed above would be adversely affected by the 1975 em~ssion-control systems. Information received from manufacturers indicated losses in acceleration capability rang- ing from a minimum of 5 percent to a maximum of 20 percent over 1971 levels. All manufacturers anticipated losses in driveability, in some cases indicated to be severe. Anticipated increases in fuel consump- tion ranged from 5 to 15 percent for standard sized cars up to 20 to 30 percent for small cars, again over 1971 levels. Much of the dete- rioration in performance was anticipated to come with the introduction of NOX requirements in 1973, and early reports on performance of the new models have confirmed this. During 1972, the CAVE has received reports on both the 1975 and 1976 emission-control system progress. While manufacturers are still concerned with performance, particularly fuel consumption, the concern over vehicle driveability has diminished. No substantial new acceleration, fuel economy, or driveability problems are introduced with the 1976 emission-control systems com- pared with the 1975 systems. At the same time, considerable progress has been made in finding solutions to problems that appeared to be very serious one year ago. It seems likely that. competitive pres- sures will result in further improvements and improved reliability in these performance areas. The effort required is essentially engi- neering development based on extensive field experience with these new systems. The major long-tenm concern should be the continuing fuel - 64 -

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economy penalty which results from the decreased compression ratio to allow the use of unleaded fuels, compounded by the use of EGR to cor~- trol NOX emissions to very low levels, and aggravated by the increased engine sizes introduced to compensate for the loss in performance. 3.11 Alternative Fuels One approach to reduce emissions from conventional engines is the use of alternative fuels. The use of liquefied natural gas (LNG), liquefied petroleum gas (LPG), hydrogen, and alcohols have been con- sidered by the Committee. 3.11.1 Liquefied Natural Gas and Liquefied Petroleum Gas Both industry and gove~-~ental groups have evaluated natural gas and propane (LPG) to determine their capability in reducing emis- s~ons from automobiles. One engine manufacturer showed that emission levels approaching the 1975-76 standards can be achieved, but exhaust gas recirculation is still required to reduce NOX formation to the 1975-76 standard. There is an 8 percent loss in peak engine power (350 cu. in. 1970 engine ~ from gasoline when us ing LEG and a 15 percent loss using natural gas. There is a substantial loss in fuel economy (30 percent), and driveability is unpaired. The use of LEG for start- ing and warm-up in a dual-fuel car using gasoline for conventional operation was attempted. Cold-start emissions are decreased. On an experimental natural-gas 6-cylinder engine sized for bus operation, another manufacturer showed that the use of compressed or liquefied natural gas would produce emissions which would meet 1975 standards. The 1976 NOX standard could be met only with EGR, a cata- lytic after-burner, and a great reduction in performance. The emis- sions were odorless and there was no particulate matter present. - 65

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There are over 5,000 cars converted to run on gaseous fuels in the Los Angeles basin where gas supplies and liquid systems have been joined together to provide the gaseous fuels to the car operators. Emissions are cleaner, maintenance is reduced, but a heavy bulky tank is required to hold the gaseous fuel. 3.11.2 Status of Liquefied-Gas Substitutes for Gasoline The COVE has investigated the technical problems and economic factors involved in supplying natural gas and LPG. It is possible to modify the petroleum refining process so that LPG can be substituted for gasoline for motor vet ales. The original capital costs would be in the $50 billion range. The fuel costs to the customer would be about twice as much as gasoline presently costs. Also, there is a serious net loss of energy in changing from gasoline to LPG. The percentage of crude oil consumed in the processing operations would increase from about 4 percent to about 14 percent. This would be an unrecoverable was te of natural resources . There is not enough LPG, LNG, or Synthetic Natural Gas (SNG) currently available to be significant if conversion were desired now. A three-year lead- time for making changes for supplying these alterna- tive fuels is a minimum. 3. 11. 3 Hydrogen Hydrogen gas has three properties which, when taken together, give it a unique potential as a vehicular fuel. Pirst, since there is no carbon in the fuel, the problems of unburned hydrocarbons and of carbon monoxide do not exist. No after-burner, catalyst, or other secondary reaction vessels are needed. Second, the flammability limits of hydrogen are extremely wide. The volume percentage of hydrogen in air can range over a factor of 19 - 66 - 1

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and still be ignited by a spark. This contrasts with the factor of 5 for gasoline vapor. Because of this high flammability range, very lean mixtures of hydrogen gas may be used, thereby insuring that NO wit 1 stay within acceptable standards. With hydrogen as a fuel, no EGR is needed to reduce NO . x Third, the supply of hydrogen gas is virtually inexhaus tible, although plants for its mass production are not yet available. Cur- rently, the cheapest way of making hydrogen gas is to use natural gas as a base material. When natural gas approaches exhaustion, the cheapest way of making hydrogen gas will be to use coal as the base material. When the price of coal becomes too high, hydrogen can be made by heating or electrolyzing water. A source of energy is required to produce hydrogen by any of these methods. An ergs ne burning hydrogen gas at s toichiometr' c ratio emits no measurable hydrocarbons, organic or sulfur compounds, and only one- tenth the NOX as when burning gasoline vapor at its stoichiometric ratio. Furthermore, at an air-fuel ratio of 1.75 times stoichiometric, the NOX composition of the hydrogen exhaust is reduced by a further factor of 20, well below the 1976 standards. Several experimenters have reported satisfactory performance from internal combustion engines converted to hydrogen fuel. The cryogenic fuel tank plus its hydrogen fuel would weigh 40 percent less than the conventional tank plus its gasoline having the same cruising radius, but would occupy five times the volume. Other storage methods are being sought. One company is attempting to produce H2 and CO2 from unleaded gasoline in the car gas tank using a small reformer located in the trunk of the car. The H2 and CO2, produced in small quantities to avoid safety problems, could be burned cleanly in the slightly modified - 67 -

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Otto-cycle engine. Questions remain on the ability of the reformer to carry out this reaction and on its efficiency, size and cost. Sound experimental work and socio-economic impact studies on the use of hydro- gen as a vehicular fuel are required before unqualified success could be claimed for the approach. In any case large-scale use of hydrogen as an automotive fuel is not possible by 1976. 3. 11.4 Alcohols Alcohol has been proposed and used as a fuel for the internal- combustion engine ; e. g., methyl alcohol is widely used as a racing fuel. Methanol has the advantage of providing a lower combustion temperature, reducing the NOx emissions, and it also has lower lean misfire limits than gasoline, thus reducing HO, CO, and NOx emissions while maintain- ing a satisfactory driveability. Emissions tests have been run on a 1970 American Motors Gremlin, using pure methanol as fuel, with a platinum catalyst converter in the exhaust. Emissions of HO, CO, and NOx, using the 1972 CVS Federal Test Procedure, were below the 1976 s tandards . Methanol has a lower heating value than gasoline, so yields correspondingly fewer miles per gallon. Starts ng at tow temperatures with methanol is a problem; volatile compounds have to be added to assure smooth starting. Similar data on ethanol are not available. Tests on gasoline with up to 30 percent ethanol as fuel show no subs tantial improvement ~ e · ~ In ems ons over pure gasoline. - 68 -

Representative terms from entire chapter:

cal cal cal