The influence of fuel and lubricants on emissions and fuel consumption
The emission characteristics of internal-combustion engines are largely dictated by the type of fuel used, although not primarily in terms of the level of pollutant concentrations but rather with regard to the components contained in the exhaust. This bec
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The emission characteristics of internal-combustion engines are largely dicta ted by the type of fuel used, although not primarily in terms of the level of pollutant concentrations but rat her with regard to the components contained in the exhaust. This becomes apparent e.g. when alternative fuels are used. Even with conventional fuels, however, the fuel composition is refiected by a spectrum of exhaust components typical for a particular type of fueI. This is why emission criteria will play an increasing role in the production of future conventional fuels [6.1].
6. 1. 1 Gasoline Gasoline for spark -ignition engines consists of a mixture of hydrocarbons that is liquid at room temperature and covers a boiling range of approx. 30°C to 215 oe. To improve cold starting, it is enriched with easily volatile constituents in winter. The following criteria are of importance forexhaust emissions and fuel consumption: • • • • •
Good starting across a wide temperature range ( - 40°C to + 50°C), Good transient characteristics (load changes) and transient operation, Low vapor-Iock tendency, High energy density, High knock resistance.
In order to meet the above criteria, specific fuel properties are required that may in certain cases have a direct impact on design and tuning of a spark-ignition engine. The main parameters are: Density, boiling curve, composition, steam pressure, heating value, octane rating, lead content, content of oxygen-based components etc. Figure 6.1 shows some important quality criteria for sp"ark-ignition engine fueIs and their effect on engine operation. Lead emissions have been reduced dramatically since "unleaded" fuel was introduced. The remaining lead emissions are caused by older vehicles that still require leaded gasoline. The gradual reduction ofthe lead content offueIs dictated by legislation standards is shown in Fig. 6.2. The main substances used to improve knock resistance of leaded gasoline, i.e. lead alkyls such as tetraethyllead (TEL) and tetramethyllead (TML), had to be replaced by fuel components with equal anti-knock properties. For economical reasons, however, these components can only be added in limited quantities [6.3]. The octane rating of unleaded regular gasoline has remained unchanged whereas it was not possible to retain the original octane rating of premium gasoline. Following harmonization of EEC specifications, the ratings for premium gasoline now are 95 RON and 85 MON (formerly 98 RON and 87 MON). The dependence of specific fuel consumption and specific work on the RON is shown in Fig. 6.3 [6.4]. This is explained by the higher compression potential that increases along with the octane rating. In addition to highly knock-resistant fueI components, a1cohols and esters are suitable as "lead re placements". The limit for adding a1cohol is approx. 3% by volume, not least of all because of limited availability [6.2]. The use of components containing oxygen is also
F. Schäfer et al., Reduced Emmisions and Fuel Consumption in Automobile Engines © Springer-Verlag Wien 1995
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