Combustion injection is the extension of HCCI range

Combustion
noise: Due to early injection the noise level increases substantially with
engine speed and load.

HC and CO
emission: HC and CO emissions were the same level compared to conventional
gasoline engines. Exhaust gas temperature was quite low.

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Nox and
particulate matter: Nox emission was 100 times lower than conventional diesel
engine and particulate matter were 10 times lower.

Effects of NADI
on engine performance:

Another advantage
of NADI is the possibility of managing early injections, as a result multiple
stage injection can be tested efficiently and its effect on the performance can
be validated. The multiple stage injection leads to a reduction of CO emission
by half and noise reduction by 4dB compared to the single injection. HC
emission persists which have to be treated in order to meet prescribed
standards. The intake pressure is lower and well-suited with turbocharger
performance. The advantage of multiple stage injection is the extension of HCCI
range without any compromise in the fuel economy.

NADI chamber is designed
with compression ratio of 14:1 to provide the same power as the conventional
diesel engine. Results indicate that HCCI combustion is favoured with the
narrowest spray cone angle.

Main objective
of NADI is to determine best combustion chamber design suitable for narrow
injection and create a homogeneous mixture. The piston bowl is modified in such
a way that there is more space under the spray to encourage fuel-air mixing
using the injection spray velocity.

·        
Multiple
stage injection

·        
Reduced
compression ratio

·        
Specific
piston bowl design for fuel guiding

·        
Narrow
spray cone angle limiting linear fuel impingement

Main differences
of NADI combustion mode compared to conventional diesel combustion include:

Injecting fuel
early helps formation of homogeneous charge but injecting too early results in
poor evaporation of fuel and leads to piston bowl spray issues. This results in
combustion event occurring earlier and hence a negative work done during the
compression stroke.

Fuel injected
towards periphery in conventional diesel engines but in NADI the fuel is
injected at the centre. Narrow angle injection prevents the fuel deposition on
combustion chamber walls, thus lowering the emissions due to unburnt fuel particles.

Narrow angle
direct injection is an approach which has the possibility of paring down the
power limitation in the HCCI engines. The aim of this method is to use highly
premixed combustion at low and medium loads while conventional diesel
combustion is used at high and full loads. Using this approach the system can interchange
between the two combustion modes.

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