Delphi Multec 3.5, Руководство по применению

Страница: 26 / 178

Fundamentals Multec 3.5 Fuel Injector Application Manual
2-10 Delphi Energy and Chassis Systems
Revision: 11/05-1
Caution Extreme transient conditions can require low pulse-widths. Commanded
pulse-widths must not fall below the application’s minimum specifications.
Inconsistencies in injector flow, pulse-to-pulse and part-to-part result
when operated below minimum recommended ranges.
2.2.6 Impact of Fuel Composition
2.2.6.1 Overview
Gasoline is a complex variable mixture of hydrocarbons, and can include
oxygenates such as ethanol, MTBE, etc. The net overall effect on
combustion depends on both the average properties of the fuel, e.g.,
average hydrogen-to-carbon ratio (H/C) and the molar percent or
molecular weight of each of the hydrocarbon species present. The lower
molecular weight hydrocarbon constituents, which are easier to burn, tend
to increase fuel volatility, making it easier to vaporize the fuel. The
higher molecular weight constituents, which are harder to burn, tend to
reduce fuel volatility. The presence of these higher molecular weight
constituents may increase the potential for engine deposits. Reference
Figure 2-3 for fuel distillation curve vs temperature properties, and the
effects of changing distillation properties on vehicle and fuel system
performance.
Fuel composition is adjusted by the fuel supply companies throughout the
year to best match the volatility of the fuel to the climate in which the fuel
is used. Reference World Wide Fuel Charter or ASTM D4814, “Standard
Specification for Automotive Spark-Ignition Engine Fuel”. Fuels outside
these specifications can compromise fuel injector performance.
2.2.6.2 Gasoline Composition – Oxygenates – Reformulated Gasoline (RFG)
As part of the U.S. Clean Air Act of 1990, oxygenated fuels are required
in ozone non-attainment areas to help reduce CO emissions. Oxygenates
help reduce the reactivity of the exhaust gas, and thus help reduce smog
formation. The California Air Resource Board (CARB) has phased out
the use of MTBE as an oxygenate. CARB Phase III fuel was introduced
during 2003 and uses ethanol as the oxygenate. In addition, many states
in the US have or are planning to phase out MTBE.
MTBE and Ethanol are common oxygenates used to provide the additional
oxygen in the combustion process to reduce CO emissions. Oxygenates
have higher stoichiometric air fuel ratios (rich relative to standard
gasolines) for optimum combustion, due to a reduction in the energy