Fuel, Economy

In practice, the user prefers the densest possible motor fuel that is compatible with the specifications, for it gives him the best volume NHV and highest fuel economy. It is estimated that an increase in density of 4 to 5% brings a reduction in consumption of 3 to 5%. Finally for the refiner, a margin of 50 thousandths accorded for the density of each type of gasoline, makes an acceptable compromise, while a tightening of the specification would be too constraining. 

Fuel economy Fuel-fired furnaces Fuel gas Fuel oil... 

In the first years of gasohol use some starting and driveabiUty problems were reported (19). Not all vehicles experienced these problems, however, and better fuel economy was often indicated even though the energy content of the fuel was reduced. Gasohol was exempted from the federal excise tax amounting to a 0.16/L ( 0.60/gal) subsidy. Without this subsidy, ethanol would be too expensive for use even as a fuel additive. 

Of course, FFV drivers do not have to use methanol. Emissions benefits are not obtained if methanol is not used, and fuel economy is not optimized for methanol nor are emissions. However the State of California has concluded that advantages offered by the flexibiUty of the FFV far outweigh the disadvantages (37). 

The first methanol bus in the world was placed in revenue service in Auckland, New Zealand in June 1981. It was a Mercedes O 305 city bus using the M 407 hGO methanol engine. This vehicle operated in revenue service for several years with mixed results. Fuel economy on an equivalent energy basis ranged from 6 to 17% mote than diesel fuel economy. Power and torque matched the diesel engine and drivers could not detect a difference. ReHabiUty and durabihty of components was a problem. Additional demonstrations took place in Berlin, Germany and in Pretoria, South Africa, both in 1982. 

Auckland Regional Authority converted two M.A.N. buses to use a cetane improver and methanol and South Africa investigated the use of methanol with a proprietary cetane improver. Eour Renault buses were converted in Tours, Erance to operate on ethanol and a cetane improver, Avocet, manufactured by Imperial Chemical Industries (ICI). The results of these demonstrations were also technically successfiil slightly better fuel economy was obtained on an energy basis and durabiUty issues were much less than the earlier tests using dedicated engines. 

Eor a considerable period, >90% of the new cars in Brazil operated on E96 fuel, or a mixture of 96% ethanol and 4% water (82). The engines have high compression ratios (ca 12 1) to utilize the high knock resistance of ethanol and deUver optimum fuel economy. In 1989 more than one-third of Brazil s 10 million automobiles operated on 96% ethanol/4% water fuel. The remainder ran on gasoline blends containing up to 20% ethanol (5). 

Fuel economy, typically expressed as distance driven per volume of fuel consumed, ie, ia km/L (mi/gal), is measured over two driving cycles specified by the Federal Test Procedure (63). Oae cycle simulates city driving and consists of relatively low speed (- 32 km/h) driving, and iacludes a portion where the car starts after having equiUbrated at ambient conditions for 16 hours. The second simulates highway driving conditions and iacludes higher speeds and... 

Fuel economy is measured usiag a carbon balance method calculation. The carbon content of the exhaust is calculated by adding up the carbon monoxide (qv), carbon dioxide (qv), and unbumed hydrocarbons (qv) concentrations. Then usiag the percent carbon ia the fuel, a volumetric fuel economy is calculated. If the heating value of the fuel is known, an energy specific fuel economy ia units such as km/MJ can be calculated as well. 

Fig. 5. Fuel economy vs energy content for various fuels. Each data poiat represents the average of twenty 1989 vehicles. To convert MJ/L to Btu/gal,...

Requirements for tire cord material will to some extent be driven by new vehicle trends. Eor example, the clean air emphasis in North America places lightweight vehicles and materials at a premium. Eor tire cord the fuel economy or rolling resistance provided by the cord—mbber composite may shift the pattern of usage. A common requirement for all types of tire cord surfaces is a high strength-to-weight ratio. 

The best power is achieved slightly rich of stoichiometric air/fuel the best fuel economy is achieved slightly lean of stoichiometric mixture. 

Two engines are under development as of this writing the two-stroke engine and the lean bum engine. The driving forces behind this development are fuel economy and global warming (see ATMOSPHERIC MODELS). 

---