This document provides an introduction to engine combustion concepts. It discusses the basics of combustion including the key metrics used to evaluate combustion efficiency. The three main combustion regimes for engines are described as stratified charge spark ignition (SI), compression ignition (CI), and homogeneous charge compression ignition (HCCI). Several advanced combustion concepts are also outlined, such as dual fuel (DF), partially premixed compression ignition (PPC), and reaction controlled compression ignition (RCCI). Optical diagnostics for visualizing combustion are briefly covered. Examples of different combustion regimes in engines are shown.
3. Engine specific issues in
combustion
Engine
combustion
basics
Highly transient phenomenon.
Combustion timing and duration are
most are important for the efficiency.
Concepts ”Heat release”, ”Rate of heat
release” and ”Combustion efficiency”
are used to indicate chemical energy
conversion to heat.
Heat is the further converted to
mechanical work with ”process
efficiency”, resulting in the thermal
efficiency of the engine.
4. Cylinder pressure and heat
release graph as function of
crank angle
Basshuysen & Schäfer Internal Combustion
Engine Handbook
Engine
combustion
basics
5. Basic combustion regimes
Premixed flame propagation,
stoichiometric or lean charge
controlled by turbulence.
Low efficiency, knock, pumping
losses, large speed range.
Three way catalyst and particulate
filter. Low reactivity fuel preferred.
Low temperature combustion,
lean and/or diluted charge,
controlled by combustion
chemistry, highest efficiency,
combustion control is
challenging. Low emission levels
due to low local temperatures
and homogenous charge, easy
premixing of fuel preferred.
Diffusion combustion, lean
charge, controlled by mixing,
high efficiency, moderate speed
range, spray physics in main
role. High NOx and PM
emissions, DPF and SCR, high
reactivity fuel preferred.
SI combustion
CI combustion
HCCI combustion
6. Most common way of
optical diagnostics is
observe combustion
though a transparent
piston.
Optical
combustion
diagnostics
Liner
Piston
Extension
45° Mirror
Protection
Glass
Cylinder
Head
CCD
Camera
Mechanical
Shutter
Common
Rail
Aalto University Optical Diagnostics
15. Conclusions
Engine
combustion
basics
• There are three basic combustion
concepts SI, CI and HCCI. Several
advanced concepts exist with focus on
high efficiency and low emission levels.
• Combustion timing and duration are
most are important for the efficiency.
• Low combustion temperatures and lean
and dilute conditions are essential for
low emission level.
• There is still plenty of room for
combustion development of engines.
16. Acknowledgements
• Richard van Basshuysen and Fred Schäfer: Internal Combustion
Engine Handbook
• Sandia National Laboratories, Mark Musculus
• US DOE, Gurpreet Singh
• Aalto University, Research Group of Energy Conversion
• Wärtsilä
• Mazda