The Diesel EngineThe diesel internal combustion engine differs from the gasoline powered Otto cycle by using a higher compression of the fuel to ignite the fuel rather than using a spark plug ("compression ignition" rather than "spark ignition").
It is convenient to express this efficiency in terms of the compression ratio r_{C} = V_{1}/V_{2} and the expansion ratio r_{E} = V_{1}/V_{3}. The efficiency can be written and this can be rearranged to the form
For an air standard engine with γ = 1.4 , compression ratio r_{C} = 15 and expansion ratio r_{E} = 5, this gives an ideal diesel efficiency of 56%. The diesel cycle depends upon this temperature being high enough to ignite the fuel when it is injected. *psig is pounds per square inch gauge pressure. Common pressure gauges in the U.S. measure pounds per square inch excess over atmospheric pressure.

Index Heat engine concepts Reference Devins Ch 4  

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Diesel Engine Theoretical Efficiency
The efficiency can be expressed in terms of the specific heats and temperatures. Now using the ideal gas law PV=nRT and γ = C_{P}/C_{V}, this can be written Now using the fact that V_{a}=V_{d}=V_{1} and P_{c}=P_{b} from the diagram Dividing the numerator and denominator by V_{1}P_{c} Now making use of the adiabatic condition PV^{γ} = constant, the efficiency can be written

Index Heat engine concepts References Devins Ch 4 Wark and Richards Ch 15  

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Diesel Engine CycleThe term "compression ignition" is typically used in technical literature to describe the modern engines commonly called "Diesel engines". This is in contrast to "spark ignition" for the typical automobile gasoline engines that operate on a cycle derived from the Otto cycle. Rudolph Diesel patented the compressionignition cycle which bears his name in the 1890s.

Index Heat engine concepts References Devins Ch 4 Wark and Richards Ch 15  

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