FIGURE 4-4 Research roadmap for 52.9 percent thermal efficiency by 2019. SOURCE: Provided under license by Cummins Inc. Copyright 2009 Cummins Inc. All rights reserved.

FIGURE 4-4 Research roadmap for 52.9 percent thermal efficiency by 2019. SOURCE: Provided under license by Cummins Inc. Copyright 2009 Cummins Inc. All rights reserved.

TABLE 4-1 Diesel Engine Fuel Consumption (percentage) by Years and Applications

Application

2013-2015

2015-2020

Tractor trailer

10.5

20

Class 6 box truck

9

14

Class 6 bucket truck

7.2

11.2

Refuse truck

10.5

14

Urban bus

9

14

Motor coach

10.5

20

Class 2b pickup and van

14

23

SOURCE: TIAX (2009).

larger engine in the same vehicle, and consequently will have a lower pumping loss than the corresponding larger engine. As an approximate guide, pumping losses might range from 2 to 5 percent of the fuel energy (Patton et al., 2002).

Compared to diesel engines, spark ignition engines are generally simpler and less expensive, they have more effective and lower cost exhaust emissions aftertreatment systems, and they have higher fuel consumption.

The current emphasis in the development of spark ignition engines is on reducing fuel consumption. Figure 4-5 gives a qualitative partitioning of the fuel energy for a typical gasoline-fueled vehicle. This is analogous to Figure 4-1, which gives an energy partitioning for diesel-powered vehicles. Figure 4-5 is illustrative in describing the technologies being considered to reduce gasoline engine fuel consumption.

The proportion of the fuel energy that gets converted into indicated work is a direct measure of the engine’s fuel conversion efficiency. Factors that affect an engine’s fuel conversion efficiency include irreversibilities18 in the combustion process, the amount of energy leaving the engine cylinder as heat transfer, and the energy remaining in the exhaust at the end of the expansion process. These losses represent fuel energy that did not get converted into useful shaft work. Not all of the energy that was converted into work in the combustion process makes it to the final shaft output.

18

Irreversibility is a thermodynamic concept. It is used to describe and quantify the degree of imperfection in any real process. In the context used here it describes the degradation of energy during the combustion process into a form that is less capable of being converted into work. Theoretically it is possible to convert all of the chemical energy contained within the fuel completely into work. Inherent in the chemical reaction of the actual combustion process are irreversibilities that render the resultant thermal energy of the combustion products not completely available to be converted into work, even though the quantity of energy is conserved.



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