Such mixtures are enabled by the diesel combustion process. Lean fuel mixtures are thermodynamically more efficient than rich mixtures because of the higher ratio of specific heats. The diesel thermodynamic cycle is shown on a P-V diagram and compared with the Otto cycle representation of the SI engine in Appendix D. The diesel thermodynamic cycle efficiency advantage over the more common spark-ignition (SI) gasoline engine stems from three major factors: the diesel engine’s use of lean mixtures, its lack of need for throttling the intake charge, and its higher compression ratios. Light-duty CI engines operating on diesel fuels have the highest thermodynamic cycle efficiency of all light-duty engine types. Estimates of effectiveness in fuel consumption reductions and costs are developed throughout the chapter, and a complete set of estimates for the diesel technologies applied to a midsize car, a large car, and a large light truck are provided in Table 3A.1 for effectiveness of reduction in fuel consumption and Tables 3A.2a, b, and c for direct manufacturing costs (see annex at end of this chapter).ĬOMPRESSION IGNITION ENGINE EFFICIENCY FUNDAMENTALS
The chapter concludes with the committee’s findings and recommendations regarding diesel engines. New and emerging technologies, including the use of alternative fuels in diesel engines and advanced combustion systems, are discussed. The low market share penetration of diesel-engine-powered vehicles in the United States currently and the role of these vehicles in achieving the 2017-2025 CAFE standards will be discussed. The incremental retail prices of diesel-powered vehicles relative to gasoline-powered vehicles are reviewed together with the current and projected future diesel vehicle offerings. This is followed by a discussion of estimated incremental costs of diesel engines relative to baseline gasoline engines.
The next section discusses the available technologies for reducing fuel consumption, carbon dioxide, and criteria emissions in advanced diesel engines. This chapter begins with a review of the fundamentals of CI engines and their role in the 2017-2025 MY final CAFE rulemaking. In contrast, diesel engines have significantly penetrated the Class 2b pickup and van market, with approximately 50 percent market share in 2014, and the light-duty passenger car and light truck vehicle market in Europe, with approximately 56 percent market share in 2013. light-duty vehicle market, consisting of Class 1 and 2a 1 passenger cars and light trucks, with less than 1 percent of new LDVs sales in 2014. However, the diesel engine has not penetrated the U.S.
The compression-ignition (CI) diesel engine has long been used in the over-the-road, heavy-duty-vehicle sector of trucks and buses in the United States and is recognized as the most fuel-efficient internal combustion engine. Without a positive displacement pump, the air on top of the rising piston would overcome the fuel pressure and force air backward into the fuel line.Technologies for Reducing Fuel Consumption in Compression-Ignition Diesel Engines These "positive displacement" pumps develop the very high and stable fuel pressures needed to inject fuel against the compressive force of a rising piston. A direct injection pump is almost identical in form and function to a tiny four-stroke engine, but passes liquid diesel fuel instead of air and fuel.
One interesting component that sets direct injection apart from other types is the fuel pump. This makes the combustion event much faster, quieter and more powerful than it would otherwise be. These injectors sit about where the spark plug would be on a gas engine and work well with diesel engines because they can introduce huge amounts of fuel into the combustion chamber just as the piston reaches its peak compression. These systems use a powerful, positive displacement fuel pump to pump diesel through injectors mounted directly in the cylinder. Direct injection has been used on diesel engines since the 1950s.