Automotive Fuel Economy How Far Can We Go? (1992) / Chapter Skim
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2 FUEL USE IN AUTOMIBILES AND LIGHT TRUCKS
2 FUEL USE IN AUTOMIBILES AND LIGHT TRUCKS
Pages 30-46
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From page 30... ...
, driver behavior, and driving conditions. All contribute importantly to the total national consumption of gasoline, diesel, and other fuels for automobiles and light trucks.
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From page 31... ...
It is also not possible to attach precise quantitative values to each of the energy flows because the distribution varies greatly depending on operating conditions. A vehicle that is optimized for fuel economy at highway speeds might have unacceptable performance in the stop-start usage of urban travel.
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From page 32... ...
is a composite of energy use under a variety of operating conditions. Automotive designers and engineers must optimize the vehicle and its power train to meet the often-conflicting demands of customer satisfaction, fuel economy requirements, emissions standards, and cost in the variety of operating conditions under which the vehicle watt be used.
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From page 33... ...
In this way, a portion of the fuel energy released during engine operation is transformed into mechanical energy of the rotating crankshaft, which is then available to propel the car, operate accessories, and overcome frictional losses in the drivetrain. All the pistons are attached to a common crankshaft in such a way that the expansion stroke of each cylinder occurs at different times.
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From page 34... ...
At decreased load, a greater fraction of the indicated work goes to overcoming pumping loss and friction. Consequently, reducing pumping losses and engine friction will significantly improve fuel economy for engines that operate at light load much of the time.
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From page 35... ...
' Pumping losses ' ~ Accessories Indicated , Engine , Transmission Work ' Output ' ~ Inertia ' (Brake work) , Vehicle ~C Losses I, Aerodynamic drag: ' ~ Rolling resistance: FIGURE 2-1 Where the energy in the fuel goes (proportions vary with vehicle design and operating conditions)
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From page 36... ...
ARE 2-2 Ilbstra1~e disk1butiou of energy released in 1be engine as ~ Unction of my: Ad ~ ~ (1991)
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From page 37... ...
A vehicle's acceleration performance is directly related to the torque exerted on the driving wheels, which is proportional to the engine torque conveyed through the transmission and drivetrain. Thus, deliverable torque, which depends on both engine speed and load, is a significant parameter of engine performance.
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From page 38... ...
than the standard Honda engine with the same displacement. Alternatively, the V¢C engine 6Increasing the ambient air density increases the mass of air in the cylinder and consequently increases torque and power output.
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From page 39... ...
However, not all technologies to improve fuel economy necessarily require compromises of other performance attributes. For example, multipoint fuel injection, which enables more precise fuel metering and control, not only improves fuel
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From page 40... ...
estimates of the cost of using the technology. Among other data, AppendLx E includes estimates of the market share of each of the proven technologies in the current fleet and the comm~ttee's judgments about the potential future market share of each.
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From page 41... ...
Accessories Accessories Electric power steering Rolling resistance Advanced tires Inertia Weight reduction Front-wheel drive Aerodynamic drag Aerodynamics Emerging technologies Lean-burn engine Two-stroke engine Active noise control Lean NOx catalyst NOTE: Descriptions of the technologies and their fuel-use characteristics, along with estimates of their costs, are provided in Appendix B aThe categories of proven technologies correspond to the energy pathways in Figure 2-1.
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From page 42... ...
In making decisions about which of the proven technologies to incorporate in a vehicle, manufacturers and their customers, if acting on a financially reasonable basis, will adopt proven technologies in the order of their cost-effectiveness -- that is, in the order in which they provide the most fuel economy improvement for each dollar invested in them. Beyond higher fuel economy, some proven technologies offer other desirable attributes to producers and consumers, such as enhanced acceleration performance or better control over emissions.
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From page 43... ...
Lean-burn engines are designed and operated so that excess air over and above that needed for complete combustion is introduced into the combustion chambers.8 Because of its potential for increased fuel economy, the homogeneous lean-burn approach was investigated extensively in the 1960s and early 1970s as an alternative emissions control approach to the three-way catalyst, which requires use of a stoichiometric air/fuel mixture that leads to lower fuel economy.9 However, the leanburn engine was unable at that time to meet emissions and drivability requirements and its development was discontinued. Its current revival is due to its acknowledged fuel economy advantage and the availability of electronic fuel injection, which makes possible operation under lean-burn conditions in selected portions of the driving cycle.
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From page 44... ...
In automotive applications, this approach offers the promise of noise control with little or no restriction on exhaust flow other than that due to the catalytic muffler required for emissions control. However, important uncertainties remain, including the magnitude of the fuel economy advantage as well as the durability, size, and cost of the necessary electronic equipment and generators of ~OEGR involves recycling a portion of the exhaust gases with the fresh air charge.
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From page 45... ...
Each of the pathways of energy use or loss offers the potential for fuel economy improvements. Automobile engineers must seek to optimize the vehicle and its power train to meet the often-conflicting demands of improved fuel economy, customer satisfaction, emission standards, safety, and cost.
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From page 46... ...
Presented to the Technology Subgroup, Committee on Fuel Economy of Automobiles and Light Trucks, Detroit, Mich., July 31. Honda Motor Company, Ltd.
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