December 16, 2019

Miers found to decrease with increase in amount of

Miers
et al. (2008) studied effect of 20% and 40% by volume blends of
butanol-diesel on the performance and emission on an unmodified diesel car in
steady state and dynamic operation. Fuel consumption was found to increase with
increase in amount of butanol in the blend. HC and CO emissions found to
increase because of poor combustion efficiency. Smoke emission was found to
decrease with increase in amount of butanol in blend.

Influence of butanol addition into diesel fuel was studied with 8%,
16% and 24% (by volume) n-butanol amount was used, on the
performance and exhaust emission in a single cylinder four stroke direct
injection diesel engine. Three different loads namely 1.4, 2.57 and 5.37 bar
BMEP were tested at a speed of 2000 rpm while static injection timing was kept
at 29 CA before top dead center (bTDC). Smoke and NOx was found to decrease at
all loads as amount of butanol increase in blends as compared to neat diesel.
However, HC and CO emissions were found to increase with increase in amount of
butanol in blend. BTE was found to increase a little this is because higher
premixed combustion because of lower cetane number of blend leads to higher
constant volume combustion. In another study Rakopoulos studied effect of
blends of butanol-diesel (8% and 16% (by vol) n-butanol), on exhaust emission
and performance in a six cylinder turbocharged diesel engine. Addition of
butanol into diesel reduce cetane number of blend, ignition delay also increase
this increase premixed combustion part and results in better BTE. Peak of HRR
was higher with blends as compared to pure diesel case. NOx, smoke were found
to decrease with increase in amount of butanol in the blend. However, HC was
found to increase.  

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Mingfa
et al. studied influence of n-butanol in diesel (0, 5, 10 and 15% of butanol by
volume) on emission and performance on a heavy duty diesel engine while blend
was injected into multiple pulses (pilot-main-post). Experiments were conducted
at a fixed speed and load however EGR is adjusted to keep NOx emission at 2.0
g/kW-hr. They observed that addition of butanol helped in reduction in soot and
CO emission without having much impact on BSFC at a constant specific NOx
emission in case of single pulse injection. In addition to this the higher the
amount of butanol is blend it resulted in more premixed combustion phase. In
double injection (pilot and main) for close pilot to main offset soot was
higher as compared to single pulse injection of B10. However, as pilot to main
offset increases soot was found to decrease (reason is not given). CO emission
was found to increase with pilot to main offset. Post injection with B10, soot
and CO emission was found to decrease as main to post offset increase this is because
of post injected fuel burns and release heat which helps in oxidation of formed
soot. In case of B10, post injection results in 46.4% (maximum) reduction in
soot as compared to single injection.

Zheng
et al. (2013) studied effect of various blends of butanol-diesel on
emissions and performance at different loads in a high
speed direct injection diesel engine. Blends of
diesel fuel with 0%, 20%, 30% and 40% of butanol (by vol) were directly
injection into combustion chamber. With butanol-diesel blends burning
rate accelerated and combustion pressure increased this was because
of ignition-delay increase and this resulted in
more amount of fuel was burning in pre-mixed phase of combustion.
However, maximum power and torque was not influenced
much. In addition to this with blends of butanol-diesel BSFC and BTE both was
found to increase. Under low loads CO emission increased and NOx
decrease with increase in amount of butanol. However, under high load
opposite trend observed. Here CO was found to decrease and NOx was found to
increase with increase in amount
of butanol. Smoke was found to decrease with increase in amount
of butanol at all loads.

Choi
et al. (2015) studied influence of blend of n-butanol with
diesel fuel on emission in a turbocharged diesel engine equipped with common
rail direct injection and results were compared with neat diesel case. In this
study 0%, 5%, 10% and 20% (by vol)
n-butanol blended with diesel. Experiments were performed
on European Stationary Cycle (ESC) test, engine
performance and emissions were measured. Fourier
Transform Infrared Spectroscopy (FTIR) was used to measure emissions of HCs,
CO, NOx, HCHO, HCOOH and NH3. Scanning
Mobility Particle Sizer (SMPS) used to measure Size and number distribution of
particulate matter (PM). THC and CO emissions were
found to increase with butanol-diesel blends this was because increase in
latent heat of vaporization and decrease in cetane number. With
n-butanol-diesel blends at all operating conditions NOx
emission was found to decrease, further with increase in amount of
butanol NO2 was
increased. In NH3-SCR applications NO2
is useful in fast reaction of de-NOx system. With B20,
HCHO emission were higher at lower loads and lower
at higher loads as compare to neat diesel operation. With
increase in amount of n-butanol in blends nano-sized PM under 50 nm
were emitted lowered.

On
the whole butanol-diesel forms a stable
blends and it helps in simultaneous reduction
in NOx and smoke emissions with
increase in BTE. However, HC and CO emissions were found to increase.    

2.3.2. Neat
butanol operation in diesel engines –

N-butanol
has lower cetane number, high octane number
(resistance to auto-ignition) and higher latent heat of
vaporization as compared to diesel these create some
problems in use of neat butanol in a conventional
diesel engine. So for utilizing neat
butanol in a diesel engine following methods are employed –

A.   
Injection of butanol along with
preheated air and auto-ignition is governed by air temperature Maurya,
2014.

B.    
Port injection of butanol
into air, increase intake
pressure of air by boosting it (upto 1 bar
gauge) so boosting helps
in auto-ignition as it reduces ignition delay Yanai, 2014.  

C.    
As boiling point, density
and viscosity are near to
diesel fuel butanol can be injected directly at
high pressure into combustion chamber Han, 2013.

However,
following modification are needed for accommodating
neat butanol as a fuel in diesel engine –

A.   
Port-fuel injection system
installation it consists of injectors (gasoline type),
fuel pump (injection pressure upto 10 bars) and a fuel tank for storing butanol.

B.    
As butanol has lower
Lubricity then diesel so a Lubricity improver
should be added while using it in a high-pressure injection system for the safety of moving parts Han, 2013.

C.    
An electric heater is
required to heat air is required
if preheated air is used for
auto-ignition of butanol which was injected into intake port.

D.   
As butanol is corrosive,
rubber and plastic parts have to be replaced with materials which can tolerate alcohols Jin, C.
2011.   

Maurya
et al. 2014-JERT did study on a four cylinder DI diesel engine, one of
which was used for research purpose which was having
compression ratio of 17.5:1, engine was
modified to run in HCCI mode of operation. Butanol was injected into
intake manifold and homogenous mixture was prepared,
preheating of intake-air was used to auto-ignite homogenous
mixture of air and butanol. Effect of air-fuel ratio and intake air temperature
was studied. However, it is noted that while
calculating efficiency in this study they did not
considered the amount energy spent in preheating the air. They
observed to gasoline has higher operating range for
HCCI than butanol. In addition to this gasoline resulted in better
ITE (because of better combustion efficiency) and lower
ISFC as compared to butanol. Very low
levels of NOx emission were observed. However, HC and CO
emissions were higher as compared to conventional diesel engine. With
increase in speed operating range for HCCI mode decreased for both
fuels.

Han
et al. (2013) studied use of
n-butanol in a diesel engine using two strategies, i.e. PFI of
butanol while disabling DI of diesel and high pressure DI of butanol. In case of
butanol in PFI mode high amount of EGR (51-57%) required for controlling
combustion phasing and it resulted in ultralow levels of NOx and
smoke emissions. They observed that n-butanol
in direct injection under high pressure shows promising results. Near zero soot
emissions were observed this was
because of longer ignition delay of butanol resulted in better mixture preparation.
In addition to this butanol has oxygen atom in its molecule. With moderate
intake boost and EGR it was possible to attain IMEP between 1 to
1.3 MPa and resulted in simultaneous reduction of NOx
and smoke emissions. However peak pressure rise rate was a problem in extending
load range.

Zheng
et al. studied n-butanol in HCCI mode in a high
compression diesel engine. Effect of EGR and intake boost on
combustion phasing and controllability was evaluated. In case of
n-butanol HCCI mode from low to medium engine loads ultralow
soot and NOx emissions were observed without use of EGR.
However, in case of diesel HCCI it depends on high levels of dilution. Under these
condition boost was not having much influence on emissions. Further
based on trade-off between thermal efficiency and combustion
instability decides levels of boost required. In
addition to this ITE was 43-46% which is comparable to diesel
combustion this was because lower reactivity of n-butanol results
in optimal combustion phasing. With n-butanol as load
increases peak pressure rise rate increases and it limits the
load. So EGR and boost is required to limit the peak pressure rise
rate and adjust the combustion phasing for better thermal efficiency. With
butanol HCCI load range was extended upto 10 bar
IMEP, which is 25% higher than which can be achieved
with diesel with higher performance and ultra-low NOx and smoke
emission.

In
another study, Yanai et al. (2015) used the same research engine
in the above study in butanol-PFI and butanol-DI
(injection pressure 90 MPa) mode at a constant speed of
1500 rpm. They have studied influence of injection timing, intake boost and EGR
on engine performance, combustion
and emission. Butanol-DI require low amount of EGR as
compared to butanol-PFI in order to control rate of pressure rise (ROPR). In case
of butanol-DI can be easily be controlled by delaying injection
timing of butanol. Both butanol-PFI and DI resulted in
simultaneous reduction in soot and NOx emission. However butanol-DI resulted
in a little higher NOx as compared to butanol-PFI. For same
NOx and ROPR butanol-PFI resulted in lower ITE as compared
to butanol-DI because of improper combustion phasing.
In both cases HC and CO emissions were high as compared to diesel engine.

It is seen
from literature n-butanol can be used as a sole fuel in CI engine but
it need some modification in engine
side as well as fuel side. However,
it can be used from low to medium load. This is because as load increases rate
of pressure rise rate also increases and it restrict
load that can be achieved. Very high
amount of EGR is required to extend load.   

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