The CI engine combustion procedure is extremely complex
− It depends on
- the characteristics of the fuel
- the pattern of the engine's combustion sleeping room and
- fuel-injection system
- the engine's operating conditions
The procedure is an unsteady, heterogeneous,three-dimensional combustion process.
Some of import consequences of diesel combustion are every bit follows:
- Injection commences but earlier the combustion starts, in addition to then at that topographic point is no knock restrain every bit inwards SIE – hence
- a higher compression ratio tin hand the axe last used improving its fuel conversion efficiency.
- Since injection timing is used to command combustion timing, delay menses betwixt the start
- of injection in addition to the get-go of combustion must last kept curt (and reproducible)
- A curt delay is likewise needed to concord the maximum cylinder gas pressure level below the maximum theengine tin hand the axe tolerate.
− The spontaneous ignition characteristics of the fuel-air mixture must last held inside a specified range
- Thus requiring the diesel to bring a cetane release inwards a higher house a sure as shooting value.
- Since engine torque is varied past times varying the amount of fuel injected per cycle alongside the engine wrap essentially unchanged, the engine tin hand the axe last operated unthrottled – thereby, reducing pumping requirement, in addition to improving part-load mechanical efficiency relative to SIE.
- As the amount of fuel injected per cycle is increased, problems alongside air utilization during combustion Pb to formation of excessive amounts of soot which cannot last burned upward prior to exhaust.
− Excessive soot or dark smoke inwards the exhaust constrains the F/A ratio at maximum engine ability to values 20% (or more) thin of stoichiometric.
Hence the maximum imep (in a n.a. engine) is lower than values for an equivalent SIE Because the diesel ever operates alongside thin F/A ratio (more in addition to then at business office load), the effective value of over the expansion procedure is higher than inwards SIE
− This gives a higher fuel conversion efficiency than inwards an SIE, for a given expansion ratio.
- The major occupation inwards diesel combustion sleeping room design is achieving sufficiently rapid mixing betwixt fuel in addition to air to consummate combustion inwards the appropriate crank angle interval (40 to l ) unopen to TC
- − Mixing charge per unit of measurement controls the fuel burning rate
- The hateful piston speed at maximum rated engine speed is around constant over a large size hit (bore dia seventy to 900 mm), in addition to then the maximum rated engine speed volition last inversely proportional to the stroke
Comparison of ignition systems
Principles of similitude inwards engine design