In the charge reactivity and emission formation. In

In this chapter
literature related to the properties of alcohol fuels, their production, their
use in compression ignition engine and their effect on performance and
emissions has been discussed. Butanol and ethanol which are considered as an emerging
renewable alternative fuel have been the main focus. In addition
to this, it also covers the main techniques which have been used to achieve the
combustion control, including fuel delivery method. 


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In Compression ignition
engines the fuel delivery technique is critical. This significantly affects the
engine combustion characteristics Lu, Xingcai, 2011. It controls the
in-cylinder fuel distribution, the mixing process, and the charge reactivity
and emission formation. In modern compression engines fuel delivery methods
includes port fuel injection and direct fuel injection.  

2.1.1 Port Fuel

Port fuel injection is
a relatively simple fuel supply system. In this technique fuel is delivered
through the intake port of an engine cylinder and a low pressure can be used in
the application of port fuel injection system **Bosch Auto
Parts. In port fuel injection system fuel is
injected into intake manifold, fuel and air mixing starts into intake manifold
and it continues in the cylinder. Before combustion, a fully premixed charge is
formed during the engine intake and the compression stroke. Hence, in port fuel
injection system fuel injection quantity has a greater impact on combustion
then the injection timing. However, combustion is greatly affected by intake
charge conditions like intake temperature, boost pressure, air-fuel ratio and
amount of EGR 2010-01-0163.

2.1.2 Direct Fuel Injection

conventional diesel engines direct fuel injection means
injecting fuel directly inside the combustion chamber at
the end of compression stroke. This injection method is an
effective method to prepare stratified air-fuel
mixture, hence it is possible to increase clean combustion
regime of engine operation 2001-01-0200,
2007-01-1880, 2015-01-0856. With the
help of common rail injection system, it is also
possible to regulate burn rate 2006-01-0629 and avoid early
combustion 2015-01-0860. For
auto-ignition essential range of air-fuel ratio is
provided by fuel injection system. To
explain diesel combustion during mixing-controlled burn or diffusion
combustion a conceptual model for the combusting spray has been proposed by Dec
970873. In diesel
engine before start of combustion the direct injected liquid fuel atomizes, evaporates
and then mixes with the surrounding air. Air-fuel ratio varies in wide
range from fuel-lean to fuel-rich. The common rail fuel
injection system for diesel with electronic controls has brought in great
flexibility and precision in control of injection parameters and has enabled
injection in multiple pulses within the same cycle Mahr, B., 2004, 2005-01-0212. Multiple
injection strategies in diesel engines consist of an early pilot injection of a
small quantity followed by a main injection and a post injection of a small
quantity. In automotive engines it is common to use more than three injection
pulses. The pilot injection helps in reducing combustion noise; however, it can result
in an increase in particulate matter (PM) because it reduces the ignition delay
of the diesel that follows during the main injection 2004-01-0127. The post
injection that comes after the main injection enhances mixing due to its kinetic
energy and increases the in-cylinder temperature which reduces soot by improved
oxidation 2005-01-0928, 2008-01-1191, 2009-01-2807.

injection of diesel

Chen, S.K. (2000)
studied effect of post injection on a multi-cylinder engine equipped with
common rail. It was observed that post injection was very helpful in reducing
particulate emission at optimum point without having much effect on BSFC and HC
emission, and beyond optimum point there was an increase in BSFC and HC
emissions was observed (reason for reduction in
particulate is not given in paper) (2000-01-3084).

Benajes, J. et al.
(2001) studied
influence of pre and post injection on emission and performance of a single
cylinder diesel engine. It was found that pre-injection was a good
strategy for reducing fuel consumption and smaller increase in soot emission.
Post injection reduces soot, with no effect on NOx emission while small
increase in BSFC. (reason for reduction in particulate is not given in paper)

Hotta et al. (2005)  did experiment on a single cylinder optical
research engine equipped with supercharger and common rail system and studied
the effect of post injection on emission and performance of engine. It was
found that with close-coupled post injection of diesel there is reduction in
SMOKE and HC emission (this is because of enhanced mixing and increase in
temperature), NOx was increased and ISFC was improved. Post injection take soot
which was produced due to main injection to squish area, and then oxidize it
with the soot which was already present in squish area by enhancing mixing with
fresh air and increasing temp. (In-cylinder observation, picture processing and
CFD analysis show that the jet flame of the after-injection carries the
remaining soot in the combustion chamber generated from the main injection to
the squish area, and then oxidizes that together with the soot previously
remained in the squish area, due to the promoted temperature and enhanced
mixing with fresh air.) (2005-01-0928)

Desantes, J.M et al.
did experiment multi-cylinder 1.9L diesel engine equipped with common rail
injection system, studied effect of post injection quantity and timing on
emission and performance of an engine. It was observed that the smaller post
injection pulse, higher the acceleration in end part of heat release and if it
is places near to main injection this will help in conclude combustion earlier
as compare to without post injection, due to this there was an improvement in
engine efficiency and it decreased when post injection was delayed. It was also
observed that there was no connection between main and post injection (split
flame). Soot emission was decreased with post injection this was due to
reduction in main injection quantity and post injection was not producing any
soot, because post injection quantity is so small that is was not able to
establish a stable flame. If post injection quantity was increase then soot
depends on location of post injection – it will increase if main and post is
close (temp will be higher when post injection is happening), it will decrease
if main and post spaced (temp will be lower when post injection is happening)
and lager the post injection quantity lowers the engine
efficiency. (2007-01-0915)

Vanegas, A. et al.
(2008) studied
influence of multiple injections (no of pulses and offset between them) on
engine emission. They found that Pilot injection helped in reduction in NOx but
smoke emission was increased. With three injections (pilot-main-post) NOx
emission slightly decrease and it is lower than single injection. For closely
coupled post injection smoke levels were decreased.
(Multi-cylinder common rail NO EGR VGT turbo) (2008-01-1191)

Mingfa et al. (2009)
experiments on a 6-cylinder turbocharged diesel engine equipped with common
rail to see the effect of post injection on emission and performance. Study was
conducted on constant BMEP and constant speed, it was found
that with post injection SMOKE and CO emissions reduced (this is due to post
injection there will be better mixing and it also enhance oxidation rate refer
2014-01-2634). Even NOx emission was decrease with post injection (this might
be due to decrease in peak temperature due to decrease in main injection
quantity – A
compressive study of diesel combustion and emission with post injection and an
investigation on effect high pressure post on soot and NO emission in a DI
engine)). With increase in Main-Post interval (dwell) smoke levels
was did not change
much, NOx level was decreasing (reason is not
given), CO and BSFC was increasing this is due with retarded post injection
combustion efficiency was falling. It was found that with increase in post
injection quantity NOx, SMOKE and CO emission decrease, but BSFC was
increasing. Post injection timing should be carefully calibrated because it was
found that with closely spaced post injection SMOKE levels were increasing (2009-01-2807).

Martin, J. et al.
did experiment on multi-cylinder 1.9L turbo-diesel engine equipped with common
rail injection system. They studied effect of post injection size and post
injection timing on engine performance and emission. They identified post
injection schedule which is most effective for engine out soot. The close
coupled post injections result modest reduction in soot and improvement in fuel
efficiency at the expense of higher NOx and there was large reduction in soot
with long-dwell post with higher THC emission but there is no improvement in
fuel efficiency. (2016-01-0726)

On a whole it is seen that
post injection offers reduction in smoke emission and better performance
without any significant change in NO emission, if it is injected at right time and
right amount. Multiple injection strategy in dual
fuel mode was studied in this
research work.