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

2. 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

3. 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

4. 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

5. 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

6. 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????

7. 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

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

9. 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.

11. 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.

12. 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

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

14. 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

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

16. 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):

17. 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

18. 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.