C I Engines as Automotive Prime Movers & Clues for Improvements P M V Subbarao Professor Mechanical Engineering Department Future Direction for Better Performance !!!

Rudolf Christian Karl Diesel Diesel published a treatise entitled, Theory and Construction of a Rational Heat-engine to Replace the Steam Engine and Combustion Engines Known Today. This formed the basis for his work on and invention of, the diesel engine. In his engine, fuel was injected at the end of compression and the fuel was ignited by the high temperature resulting from compression. Typical SI engines 9 < r < 11 k = 1.4

Early Diesel’s Engine Cycle and the Thermodynamic Model Fuel injected at TC Power Stroke A I R Intake Stroke Combustion Products Exhaust Stroke Air Compression Stroke Actual Cycle Qin Const pressure heat addition Process BC Qout Const volume heat rejection Process Air Compression Process Expansion Process Diesel Cycle

Air-Standard 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 Qin Cut-off ratio: Qout v2 TC v1 BC TC BC

Thermal Efficiency of Diesel Cycle For air-standard cycle: recall, Note the term in the square bracket is always larger than one so for the same compression ratio, r, the Diesel cycle has a lower thermal efficiency than the Otto cycle Note: CI facilitates higher r compared to SI to ignite fuel

Thermal Efficiency of Diesel Models Typical CI Engines 15 < r < 20 When rc (= v3/v2)1 the Diesel cycle efficiency approaches the efficiency of the Otto cycle Higher efficiency is obtained by adding less heat per cycle, Qin,  run engine at higher speed to get the same power????

Early CI Engine Cycle or Low Speed CI Engines Combustion Products Fuel injected at TC Intake Stroke Air Compression Power Exhaust Actual Cycle Fuel injection starts Early CI engine In early CI engines the fuel was injected when the piston reached TC and thus combustion lasted well into the expansion stroke. The combustion process in the early CI engines is best approximated by a constant pressure heat addition process  Diesel Cycle

The World Largest I C Engine Despite the green hype, internal-combustion engines will keep powering vehicles for the foreseeable future.

The Latest News The world’s biggest engine is the Wärtsilä-Sulzer RTA96. It’s the largest internal combustion engine ever built by man. Wärtsilä-Sulzer RTA96-C is a 14-cylinder, turbocharged diesel engine that was specially designed to power the Emma Maersk which is owned by the Danish Maersk. Wärtsilä-Sulzer RTA96, the world’s biggest engine, has a weight of 2.3 million kilogrammes. For the marine application that has a 2.5 m stroke, the engine speed is limited to 102 rpm.

Economies of Scale in Sea Transportation Maersk Lines have done the world proud by providing cheap sea transportation that is costing cents instead of a dollar per every kg weight. They are able to do this by using economies of scale in sea transportation. It is getting cheaper to ship goods from USA to China and from China to USA. It has now become cheaper to transport goods from China to a US port than to transport the same goods from a US port to the final destination inland of US by a truck.

Modern CI Engine Cycle Actual Cycle Combustion Products Fuel injected at 15o bTC Intake Stroke A I R Air Compression Power Exhaust Actual Cycle Fuel injection starts Modern CI engine In modern engines the fuel is injected before TC (about 15o) The combustion process in the modern CI engines is best approximated by a combination of constant volume and constant pressure  Dual Cycle

Thermodynamic Dual Cycle Air TC BC Qin Qout Compression Process Const pressure heat addition Expansion Const volume heat rejection Dual Cycle

Air Standard Dual Cycle Model for High Speed CI Engines 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 3 Qin 2.5 3 2 Qin 2.5 4 2 4 1 1 Qout

Thermal Efficiency of Air Standard Dual Model Note, the Otto cycle (rc=1) and the Diesel cycle (a=1) are special cases:

Design for Dual Model The use of the Dual cycle requires information about either: the fractions of constant volume and constant pressure heat addition (common assumption is to equally split the heat addition), or maximum pressure p3. Transformation of rc and a into more natural variables yields For the same inlet conditions P1, V1 and the same compression ratio: For the same inlet conditions P1, V1 and the same peak pressure P3 (actual design limitation in engines):

For the same inlet conditions P1, V1 and the same compression ratio P2/P1: For the same inlet conditions P1, V1 and the same peak pressure P3: Diesel Dual Otto Pmax Tmax Po Pressure, P Temperature, T Specific Volume Entropy Diesel Dual Otto “x” →“2.5” Po Pressure, P Temperature, T Specific Volume Entropy

The high-end version, the AUDI 3.0 TDI clean diesel TDI clean diesel has a maximum output of 200 kW and delivers 600 N·m of torque between 1,500 and 3,000 rpm. Its NEDC fuel consumption is just 4.9 liters per 100 kilometers. It emits only 129 grams of CO2 per kilometer.