Analysis of Diesel Cycle and Scope for Modification P M V Subbarao Professor Mechanical Engineering Department Creation of Rational Models for Engines…

A brief history of the diesel engine Diesel built the first diesel engine at the Augsburg Maschinenfabrik Rudolph Diesel, filed a patent application The single cylinder engine was used to power stationary machinery. It weighed five tonnes and produced 20 hp at 172 rpm! The engine operated at 26.2% efficiency, a very significant improvement on the 20% achieved by the best gasoline engines of the time Benz introduces a 2-cylinder, 30 hp 800 rpm tractor engine Benz introduces a 4-cylinder, 50 hp 1000 rpm truck engine Peugeot introduces the 404 Diesel followed by the 504 Diesel and the 204 Diesel, the first diesel-powered compact car

Displacement Work Devices : Compression Ignition Engine A I R Intake Stroke Power Stroke Air Compression Stroke Combustion Products Exhaust Stroke

Air Compression Process Expansion Process BC Q out Const volume heat rejection Process Q in Const pressure heat addition Process Active Part of the Innovation : Ideal Diesel Cycle

Process 1  2 Isentropic compression Process 2  3 Constant pressure heat addition Process 3  4 Isentropic expansion Process 4  1 Constant volume heat rejection Air-Standard Diesel cycle Cut-off ratio: Q in Q out v 2 TC v 1 BC TC BC

First Law Analysis of Air Standard Diesel Cycle 1  2 Isentropic Compression of Air AIR

2  3 Constant Pressure Heat Addition AIR Q in TC

3  4 Isentropic Expansion AIR 4  1 Constant Volume Heat Removal Q out AIR BC

Cycle thermal efficiency: Net cycle work: First Law Analysis of Air Standard Diesel Cycle

Typical CI Engines 15 < r < 20 When r c (= v 3 /v 2 )  1 the Diesel cycle efficiency approaches the efficiency of the Otto cycle Thermal Efficiency r c =1 r c =2 r c =3

Structure of Efficient Diesel Cycle Higher efficiency is obtained by adding less heat per cycle, Q in,  run engine at higher speed to get the same power.

Multi Cylinder diesel engines Diesel built the first diesel engine at the Augsburg Maschinenfabrik Rudolph Diesel, filed a patent application The single cylinder engine was used to power stationary machinery. It weighed five tonnes and produced 20 hp at 172 rpm! The engine operated at 26.2% efficiency, a very significant improvement on the 20% achieved by the best gasoline engines of the time Benz introduces a 2-cylinder, 30 hp 800 rpm tractor engine Benz introduces a 4-cylinder, 50 hp 1000 rpm truck engine Peugeot introduces the 404 Diesel followed by the 504 Diesel and the 204 Diesel, the first diesel-powered compact car

Early CI Engine Cycle A I R Combustion Products Fuel injected at TC Intake Stroke Air Compression Stroke Power Stroke Exhaust Stroke Actual Cycle

Schematic of a diesel spray & flame with temperatures and chemistry

Modern CI Engine Cycle Combustion Products Fuel injected at 35 o bTC Intake Stroke A I R Air Compression Stroke Power Stroke Exhaust Stroke Actual Cycle

Flammability Vs Inflammability Characteristics

BC Air Compression Process Expansion Process Q out Const volume heat rejection Process Slow Combustion Process TC Sudden Combustion Process Thermodynamic Dual Cycle A I R Intake Stroke

Air Compression Process Expansion Process Const volume heat rejection Process BC Q out Q in Const pressure heat addition Process TC Q in Const volume heat addition Process Thermodynamic Dual Cycle

Process 1  2 Isentropic compression Process 2  2.5 Constant volume heat addition Process 2.5  3 Constant pressure heat addition Process 3  4 Isentropic expansion Process 4  1 Constant volume heat rejection Dual Cycle Q in Q out

Thermal Efficiency Note, the Otto cycle (r c =1) and the Diesel cycle (  =1) are special cases:

The use of the Dual cycle requires information about either: i)the fractions of constant volume and constant pressure heat addition (common assumption is to equally split the heat addition), or ii)maximum pressure p 3. iii)Transformation of r c and  into more natural variables yields For the same inlet conditions p 1, V 1 and the same compression ratio: For the same inlet conditions p 1, v 1 and the same peak pressure p 3 (actual design limitation in engines):

For the same compression ratio p 2 /p 1 : For the same peak pressure p 3 : Diesel Dual Otto Diesel Dual Otto “x” →“2.5” P max T max PoPo PoPo Pressure, P Temperature, T Specific Volume Entropy

Type of Fuel Vs Combustion Strategy Highly volatile with High self Ignition Temperature: Spark Ignition. Ignition after thorough mixing of air and fuel. Less Volatile with low self Ignition Temperature: Compression Ignition, Almost simultaneous mixing & Ignition.