Effect of Injection Strategies on Wall
Impingement in Direct Injection Spark
Ignition Engines(DISI)
Sahil Gala
Department of Mechanical Engineering
Indian Institute of Technology Kanpur
Abstract:
This study was performed to analyse the wall impingement and fuel film formation in a
DISI engine with injection strategies using image-based analysis and CFD. The direct
injection engine uses a high-pressure injection strategy to improve the homogeneity of
the air-fuel mixture, so the spray behaviour was analysed by spray visualization for
various injection pressures, and the wall impingement was predicted for various engine
operating conditions based on the acquired images. The mass distribution of the injected
fuel was calculated using the injection profiles and the spray image, and the amount of
fuel that impinges on the piston and wall (i.e., the geometric boundaries of the cylinder)
was calculated using data from the spray behaviour for various engine operation
conditions such as load and engine speed. The spray injected from a six-hole injector into
a constant-volume chamber has been characterised, before and after fuel impingement
on a hot surface simulating the piston in direct-injection gasoline engines, by means of
spray visualisation and phase Doppler anemometry (PDA) measurements. Spray i
mages have confirmed that penetration decreases with increasing chamber pressure or
decreasing injection pressure, that higher droplet velocities are present at the spray
centre and that a multi layer structure is formed along the spray axis. Stronger
interaction between the six sprays is observed as the chamber pressure increases. The
PDA measurements under both atmospheric and high pressure revealed that the mean
droplet velocity prior to fuel impingement on the surface reaches its peak at the spray
axis unlike the droplet mean diameter which exhibits an off-centre peak. The results
also showed that the temporal variation of the mean droplet velocity at the spray
centreline is similar to the predicted injection velocity variation at the nozzle exit while,
further downstream and away from the centreline, three stages have been identified in
the spray structure: leading edge, steady-state and tail. After the droplets impinge on
the hot plate they move downstream forming a jet parallel to the plate surface with
increasing or decreasing mean diameter depending on the surface inclination angle. The
effect of injection pressure and ambient pressure/temperature on the droplet
characteristics has been demonstrated and quantified.
1.Introduction:
Over the years, gasoline engines have changed considerably to adhere to rules on fuel
economy, bringing about the evolution of direct injection spark ignition (DISI) engines.
These engines are characterized by accurate fuel control and enhanced efficiency.
However, challenges like particulate emissions and fuel wall film formation come in
their way. Based on previous research on atomization and wall film formation, it is
pointed out that high-pressure injection strategies can be used to improve
atomization.Also they will reduce wall film formation. Lee et al examined multi-hole
DISI injectors which produced better atomization and mixing with increased injection
pressures. Schulz et al investigated the impact of wall films, finding that it decreases
with an increase in nozzle-to-wall distance.
Wall impingement prediction can be difficult, even with the progress made over the
years in this field. In order to examine the intricate physics of spray-wall interactions,
this paper seeks to explore and understand the behaviour of spray and wall
impingement with a multi-hole DISI injector under various engine operating conditions.
The wall impingement is largely affected by the injection strategies in direct injection
spark ignition engines, whereby wall impingement refers to the fuel spray droplets
colliding with cylinder walls. In particular, this phenomenon influences combustion
efficiency and emissions. Early injection is likely to lead to wall impingement because
there will be a long period of exposure, but late injection can result in poor atomization
and distribution that increases the risk of accumulation on the walls. The use of split
injections as well as high-pressure injections would reduce wall impingement through
improved distribution of fuel, but adequate control measures are important. Similarly,
multiple injection events are also a way that could further optimize fuel distribution and
minimize contact with walls.
One of the principal elements in DISI engine improvement, as well as a decrease in
emissions, is to see how wall impingement works due to injection strategies.
1.1 Effects of the injection strategy on the mixture
formation and combustion characteristics in a DISI
(direct injection spark ignition) optical engine[2]
In internal combustion engines, the injection strategy plays a crucial role in determining
engine performance. The fuel-air mixing process is heavily influenced by the injection
timing, which in turn affects combustion characteristics. In direct injection spark
ignition (DISI) engines, the distribution of fuel near the spark plug is particularly
critical for combustion stability. Therefore, understanding the relationship between
injection strategy and combustion characteristics is essential.
While various injection strategies have been explored for gasoline engines, many have
been borrowed from diesel engines, such as split injection or high-pressure injection.
However, the concept of late injection during the compression stroke, which forms a
stratified charge, is relatively new for gasoline engines and requires further
investigation.
Sjoberg and Reuss applied stratified combustion in gasoline engines to reduce NO
emissions while maintaining high combustion efficiency and stability. They found that
closely coupled injection and spark timing contributed to high combustion stability.
High-speed flame images supported their findings, showing that early spark timing
allowed the spark plasma to develop before interacting with the fuel spray, leading to
stable combustion.
While high-speed flame images provide valuable insights into the combustion process,
many researchers also rely on in-cylinder pressure data for analyzing combustion
characteristics. Pressure data can provide information on parameters like heat release
rate and mass fraction burned, although it only offers averaged information throughout
the cylinder.
1.2 Spray break-up and atomization processes from
GDI injector using high injection pressure.[3]
In internal combustion engines, the formation of the air-fuel mixture is crucial for
engine efficiency and emissions control. Poor mixing can lead to excessive pollution and
reduced efficiency. Gasoline direct injection (GDI) engines, which inject fuel directly into
the cylinder, offer better mixture formation compared to port fuel injection (PFI) engines
due to higher injection pressures and more precise fuel delivery.
The formation of air-fuel mixtures depends on factors such as the internal structure of
the liquid jet, the atomization process, and fuel evaporation characteristics.
Understanding the internal structure of the liquid jet during injection is critical as it
affects atomization and evaporation. Spray break-up processes also play a crucial role in
engine performance and emissions.
Various studies have investigated the liquid jet development and atomization
characteristics of GDI injectors. Mitroglou et al. used Mie-scattering visualization and
phase Doppler anemometry experiments to study spray structure and atomization
processes at increasing injection pressures. They observed counter-rotating
air-entrainment vortices that contributed to spray dispersion. Postrioti et al. performed
global momentum measurements to understand spray structure and evolution processes
in more detail. Befrui et al. used computational fluid dynamics (CFD) simulations to
model nozzle internal flow and spray atomization, observing flow separation at the
nozzle entrance. Oh et al. modelled GDI spray atomization using KIVA code and
validated their results against experimental data.
Despite these efforts, the internal structure of the liquid jet and spray break-up
processes using multi-hole GDI injectors under ultra-high injection pressures have not
been fully characterized. Understanding these processes under high injection pressures,
up to 30 MPa, is crucial for further optimizing GDI engine development. In this study,
we investigated the internal structure of a liquid jet from a multi-hole GDI injector and
spray break-up processes under high injection pressures to analyze the influence of
injection pressure on jet atomization processes. By focusing on a single jet out of six, aim
is to characterize the effect of injection pressure on liquid jet break-up and atomization
processes in detail.
2. Methodologies for predicting wall
impingement in a direct injection spark
ignition engine (Pressures up to 50 Mpa)
2.1 Experimental apparatus and conditions[1]
This study aimed to determine the influence of injection pressure on spray development
and wall impingement in a vertical multi-hole side-mount gasoline engine by conducting
various experiments. A test injection kit with 6 holes was available for 33 MPa injection
system. N-heptane, used as the standard fuel, had been pressurized up to 50 MPa by air
pump.
The LabVIEW dependent embedded control system also produced an injector driving
signal while capturing scattered light images of fuel droplets using two iodine-tungsten
metal halide lamps and a high speed camera clocking at 10,000 frames per second
determined the mass distribution of fuel. The experiment was conducted under room
temperature and atmospheric pressure conditions. To decrease scatter between
injections, each image was obtained from twenty sprays.
Injection pressures were varied between 5 MPa and 50MPa inclusive. At any given
injection pressure, nozzles released either 14 mg or 25 mg of petrol depending on
whether the load was medium or high respectively. This would enable examination of
wall impingement for different engine operating conditions such as engine speed and
load settings among others. The injector driving system was synchronized with the
high-speed camera to capture spray images at the same time through an electrical pulse.
Fig. 1. Experimental apparatus for spray visualization.[1]
2.2 Image-based prediction of wall impingement [1]
The study presents a detailed methodology using MATLAB image processing to analyze
the impact of injection pressure on injection duration and spray development in engines.
The analysis includes determining spray tip penetration, calculating spray cone angle,
and evaluating fuel distribution within the spray.
The method assumes a square wave injection profile and calculates the amount of fuel
injected per unit time based on measured injection quantities and the number of image
frames during injection. This approach allows for a comprehensive assessment of how
injection pressure affects spray behaviour and development over time.
Fig. 2. Detected spray boundary and the definitions of the spray development
indices.[1]
However, the study acknowledges certain limitations. It does not account for in-cylinder
temperature and intake flow conditions, which can influence spray characteristics in
actual engine systems.
The direct lap spray on walls in the deceleration reaction of the diesel engine is very
important for both efficiency rate and emissions' control requirement. The process
involves two main phenomena: further pollutants that could lead to wall deterioration
and detrimental roof films. The latter group, which involves droplet deflection, bounce,
and splashing, is beneficial to the process as it has more area and better uniform
acceptance of the droplets, especially with regards to heating and vaporization. The
former one occurred due fuel deposition and therefore, it can lead to hazardous
environmental effects such as enhanced soot production.
Without many researchers approach of spray impingement, mostly in test chambers
which simulates standard conditions providing scarce data towards the droplet
characteristics at the corner. Computational modelling envelops an alternative that is
more accurate and therefore gives detailed analysis opportunities. The primary models
then concentrated on droplet splash (Naber and Reitz ); only they had some omissions
when it came to predicting effects close to the wall where droplet Further variants,
including the model by Watkins and Wang that considered rebound or breakup based on
impact energy, and the modified droplet collision model, were produced by subsequent
models. Nevertheless, these models still had the inadequacies and could not precisely
predict wall spray dispersion and volume.
2.3 Development of Methodology for Spray
Impingement Simulation [4]
This paper presents a new model for simulating droplet inputs on spray-wall boundaries
which gives attention to the specific attributes of impinging drops and their
consequences. The model is based on the single drop impingement processes and
conservation laws and is capable of identifying impingement regimes and characterizing
post-impingement droplets. The implementation and the evaluation against
experimental data are dealt with.
The regime switch criteria for the wall heat transfer and wetting in the spray
impingement on the wall in the direct injection Diesel engines are based on the wall
temperature and wetness. For dry walls, the transition between the adhesion to the
splash is a result of Weber number (Wec). It depends on the type of roughness. The
splashing of the walls naves a rebound and spread phase and followed by a splash. The
criteria for transition are simplified to give a sharp definition of the regimes and to
consider only a few parameters.Fig 12[2] is given below showing variation of droplet
mean velocity as function of distance of wall in DISI engines.
Post-impingement characteristics are determined based on the impingement regime:
●
Adhesion (stick/spread): Droplets coalesce to form a local film.
●
Rebound: The rebound velocity magnitude is determined using a relation for
kinetic energy loss, although this may overpredict energy loss for thin film
surfaces.
●
Splash: Total secondary to incident droplet mass ratio and characteristics of
secondary droplets are determined. Each droplet parcel is assumed to produce
two secondary parcels with equal mass but different sizes and velocities, falling
within a cone for both normal and oblique impingement.
These models and criteria help predict spray behaviour on walls, crucial for improving
combustion efficiency and emissions control in DI Diesel engines.
This method has limitations in that it cannot reflect some physical conditions in
actual engine systems such as in-cylinder temperature and intake flow. In addition,
there is a need to discuss wall-wetting and rebounding phenomena that occur after
wall-impingement in engines to analyze the effects of wall-impingement on
atomisation of droplets.
3. Spray/wall interaction in direct-injection
spark ignition engines equipped with
multi-hole injectors[5]
3.1 Introduction
The intense competition among automotive manufacturers to enhance engine
performance while minimizing engine-out global and local emissions has led to extensive
research on direct-injection spark-ignition (DISI) engines. These engines employ wide
spacing and close spacing combustion systems, depending on the proximity of the spark
plug to the injector. In wide spacing wall-guided combustion systems, the spray is
injected late during compression, impinging on a cavity in the piston that guides the
spray towards the spark plug just before ignition.
However, the swirl-type injector, which has been successful in early wide spacing
combustion configurations, tends to fail in close spacing systems due to dynamic
variations in spray structure under changing engine operating conditions, leading to
potential engine misfires. Additionally, the presence of large droplets in the pre-spray
can increase hydrocarbon emissions from the engine.
Now the researchers are emphasizing the new types of injectors, like multi-hole , slit
and outward opening pintle injectors, to solve the issues with instability, tilt and
fuel-flow rate of rocket engine. Various studies have shown that the highly stable and
repeatable multi-hole injectors spray range is wider in mass distribution of droplets
than those of swirl injectors. Thus, in the case of common-rail, multi-hole injectors are
applied. The Bosch systems have trended towards injection systems, which are able to
inject pressures that exceed typical ranges of swirl injector operation, limiting the
variability of droplet sizes.
The spray migration from the DISI multi-hole injectors has been examined as well, with
the injection pressure increase from 120 to 200 bar leading to a 14-19 μm droplet size
stability. These units have been installed into Le Mans motors used by Audi and worked
with a homogenous mixture. Nevertheless, the limited applicability of the low-cylinder
pressure injection system to other combustion systems, particularly to air-guided
combustion, is an issue in that the impaction of the spray on the hot piston, which
contributes a lot to hydrocarbon emissions during engine cold starts, has to be
thoroughly investigated.
The current work on the atomization from a multi-orifices injector is done in the two
sets of experiments one prior to and the other after the impingement on a hot surface to
represent a piston as a part of the experimental work to identify the parameters which
affect spray characteristics, combustion stability and engine out emissions. These
findings are then further used to confirm and refine an in-house spray impingement
model.
3.2 System Description
The experimental setup includes a sealed chamber having four quartz windows, which is
connected to a nitrogen cylinder by a tailpiece to generate the required pressure. Inside
the chamber, a heated plate electrically kept at specific inclination angle and distance
(31 mm) from the injector is fixed. The plate's temperature is controlled using a
closed-loop temperature control unit, with three wall temperatures investigated: cell
count - 381K (206k), 435K (242k), and 489K (262k).
Rotating imaging is obtained by installing a CCD camera and sending the light intensity
as a pulse synchrony with the injection pulses. Therefore, a very small quantity (only
one spray out of the six) is allowed to hit onto the polished surface at an angle of 60
degrees and 30 degrees. Angle of incidence is the vertical segment from the plume's
centerline to a tangent normal to the impingement body's surface.
Droplet size and velocity are measured with Phase Doppler Anemometry (PDA) detector
system. Its orientation is determined by the targeted forward scattering angle, which is
70 degrees in this example. During PDA system measurement coincidence type is
assigned so axial/radial velocities and droplet diameter can be measured at the same
time. The PC sustainable, fully automated motions of both the transmitting and
receiving optics along 3-D traverse mechanism moving relative to the constant-volume
chamber is where the mounting of both the transmitting and receiving optics take place.
Data is gathered which involves two injection pressures (70 bar and 100bar), for
chamber pressures of 1 bar, 3bar and 7bar and with an injection frequency equal to
0.25injection/second. Samples are acquired in the 0.2 ms time frame since the beginning
of the injection signal, and up to a maximum of 7 ms.
The procedure is initiated with delivering measurements into the free spray condition
where there is no impingement. Sixty readings are taken from the center and as far as
30 mm laterally in the axial direction each 2 mm until the spray edge. The sprayed free
images are then placed back, and the new measurement points situated parallel on
three planes including 1, 3 and 5 mm above the heated plate are located.
The study uses Is-Octane as the fuel, which has same properties like gasoline, but has
the advantage of being safer to compare and mathematically valid. It is a
single-component fuel with boiling point of 99°C at 0.69 kg/m3. This selection of fuel
thus complicates the simulation process and the validation of the mathematical model.
Below are the figures. [5]
3.3 Spray Visualisation results
Prior to spray imaging, the time duration from the initiation of the injection signal to
the first appearance of fuel at the nozzle exit was estimated to be 0.65 ms while the time
to the end of injection was 1.9 ms. Accordingly, for a demand injection duration of 1.5
ms, the actual injection duration is 1.25 ms. Images were then collected at different
times from the start of fuel appearance at the nozzle exit for different injection and
chamber pressures.
These images have shown that the interaction among the six sprays becomes more
significant as injection pressure increases, according to Figure 4 [5]. These images also
showed that the spray angle remains constant while the tip penetration increases with
increasing injection pressure; penetration increases until it reaches an asymptotic value
as shown in Figure 5. [5]
To accomplish with a minimum spraysitter influence, the plate mimicking the piston
was heated up to the given temperature and that was positioned under just one of the
six sprays. Along the crossline of the spray center, for a sampling position free from side
effects of the adjacent spray rings, measurements of the PDA values were obtained. The
picture from the nozzle's spray above plate at 60 Degree impingement angle shown that
as the droplets get to the plate at the impact angle, they move forward as a wall jet
along the plate surface accompanied a possibility of droplet aggregation, splash or
deposition. The lesser impact velocity observed at the new 60° incidence angle
consequently produces the velocity distribution of the reflected or splash droplets to be
lower. Accordingly, the water droplets attracted each other more powerfully along the
vertical plate compared to a 30o-degree angle, which was visualized by spray casts as
shown in above figures.
3.4 PDA Measurements
3.4.1 Before impinging (free spray)
Figure 7 [5] reveals the trend of droplet mean velocity at the distance of 30 mm from the
nozzle exit along the spray centerline in the time range between seconds 0 and 0.002.
The Scatter chart 7 shows the introduction during the injection- and the arithmetic
mean velocity. Figure 7b displays the time variation of these parameters' mean velocity,
mean diameter, and mean angle of direction in the same location for each pressure in
both filter box and chamber. The temporal variation of mean droplet velocity away from
the spray centerline can be divided into three stages: leading edge, cruise and low
approach speed, and tail. The leading edge is given to the first group of those relatively
big droplets, which "enter" the control area with little delay. There is a constant
bandwidth of droplet velocity values with the above mentioned average value for it, as
was also found out for the average droplet size. Darwinian tail, represented by droplets
after the needle seals are droplets which have low velocities due to small momentum
and inability to follow others that push the flow. Super drove pressure variations of 20
bar make mean droplet velocity double and reduce mean droplet diameter, resulting in
better primary atomization and secondary droplet break-up. To the other side the
pressure level increases the droplet velocity which in turn results in a droplet colliding
and increases the mean droplet size. Spray angle of mean droplet is invariable which
denote the constant and definite spray stability and give assurance of spray
reproducibility.
Figure 8[5] should show the trajectory model of the mean droplet velocity profile across
the plate, and therefore the droplets closer to the centerline have a higher velocity than
those towards the edge. While the reverse is true, meaning drop diameter is in its range
of amplitudes. The centerline has the highest velocity and consists of the smallest
droplet of them all. The formation of large droplets further away from the KIV could be
because of droplet aggregation from velocity decreases at the edges, and air entrainment
due to the change of curvature of the outer spray.
4 Fuel spray visualization and its
impingement analysis on in-cylinder
surfaces in a direct-injection SI engines[6]
4.1 Introduction
The creation of DISI (direct-injection spark- ignition) engines targets establishing more
fuel efficiency and reducing the amount of emissions from exhaust gases. Noordlum is
fed directly into the engine cylinder which gives an opportunity to control the timing,
duration and the number of injections. Ranking the fill fuel-air mixture homogeneity is
of utmost importance, but excessive fuel impingement levels on cylinder surfaces result
in more unburned hydrocarbons and smoke emission therefore, it may also result in
contradictory effects on fuel economy improvement. Many works survey spray patterns
fuel and their contributions to the combustion of compounds. The works in this area
included lasers, Mie scattering, high-speed imaging and they were applied to visualize
spray characteristics and for the quantification of spray behavior. Spray pattern of
injector plays vital role in fuel atmosphere mixing . The rightful choice of spray pattern
really can do wonders, as it prevents fuel impingement, and increases mixing. The
research also identified the angles of the spray as a significant factor among fuels that is
also greatly dependent on the engine temperature. Constructing an injection cone angle,
location, and time compatible with emanating flow from the injector which is milder in
intensity with impingement force at the jet exit intruding more at elevated
temperatures is possible. This article's end goal is to explore the effects of fuel
impingement onto the cylinder lining and top of piston in a DISI engine through new
image processing algorithms that will be used to analyse the data gathered. A variety of
different injection pressures, timings and number of injections have been tested in order
to understand the influence of impingement dynamics on the engines. The acquired
knowledge provides the possibility for improvement of the engines through adequate
design and implementation.
4.2 Experimental setup and procedure
The study used a 0.4-liter single-cylinder spark-ignition engine with four valves (two
intake and two exhaust) and a quartz cylinder for optical access. The engine had a bore
diameter of 83 mm and a stroke length of 73.9 mm. The experiments were conducted
with 0° crank angle corresponding to top dead center (TDC) of compression. The engine
could accommodate both low-pressure and high-pressure direct-injection fuel injectors
and either 8 mm or 14 mm spark plugs for ionization combustion feedback. A
custom-designed piston allowed for a geometric compression ratio (knock-limited)
ranging from 9.75:1 to 13.5:1.
A Mie scattering technique was used to visualize the liquid fuel dispersion inside the
combustion chamber. A Photron APX-RS high-speed CMOS camera and a Nikon 105
mm AF micro lens were used to image the fuel spray at 10 kHz. A high repetition rate
pulsed copper vapor laser was synchronized with the camera and fuel injection timing
logic to illuminate the fuel dispersion. E85 (85% ethanol and 15% gasoline blend) was
used as the fuel.
Experiments were conducted at 1500 rpm with full-load wide open throttle (WOT)
condition. Different fuel injection timings (240°, 210°, and 180° BTDC) were studied to
optimize injection timing and minimize fuel impingement on in-cylinder surfaces. The
effects of split (dual) injection were also studied, maintaining the same fuel amount as
in a single injection. Fuel injection duration at each test point was adjusted to achieve a
stoichiometric air-fuel ratio based on gasoline.
4.3 Image processing technique for fuel impingement
analysis
The experiment created innovative image-processing algorithms to assess the spray
images through impingement of fuel on cylinder surfaces, emphasizing walls and piston
top at cranck-angle degrees (CAD). In this regard valve timing and fuel delivery systems
reduce pressure, improve timing and improve number of injections, which lead to
high-performance engines.
For fuel impingement analyzing, the point of interest (POI) is firstly determined in each
frame the position of cilinder is specified in relation to a particular point, selected to
show maximum details for maximum data per block. And the dimensional limits are
then reconstructed depending on the newly identified ground position coordinates
obtained through piston motion. the Given task is completed via the technique called
normalized dot product process. This process is used either for the purpose of motion
detection of piston or for the purpose of new location of POI from the processed frame.
The researcher used a 31x31 pixel block in the first frame with the POI placed in the
center as a template pattern to cover the pixels in the current frame, and a 61x61 pixel
roam window to detect its best match. Compared with the template and window in the
roam window to find the highest absolute value of the normalized dot product then the
maximum is selected as the template's best match.
Overall, the main goal and significance of the image processing algorithms studied in
the paper is to provide a detailed analysis of fuel impingement dynamics on in-cylinder
surfaces, which will allow optimization of fuel injection parameters that are in central
for the benefit of engine performance. Below are impingement analysis figures[6].
4.4 Results of spray visualisation[6]
An assessment of the role of fuel spray in in-cylinder mixture formation and
impingement within a Direct Injection Spark Ignited (DISI) engine was the main
objective of this study. The aerosol development was studied using the E85 fuel injection
process by two type of injectors namely low-pressure direct injection and high-pressure
direct injection at 3, 5, and 10 MPa injection pressures, delaying the spark plug timing
by 240° BTDC, running at 1500 rpm, with full-load conditions. An LPDI direct injection
pump at 3 MPa stimulated a wider spray angle in comparison with an HPDI injector
which had higher pressures, while demonstrating more rapid speed of spray tip
penetration with increasing injection pressures. An injection pressure hit just the
piston’s top point by the end of the cycle and this variation between HPDI injector at 5
MPa against the LPDI injector at 3 MPa and the HPDI injector at 10 MPa have been
identified as the truth. The most relevant improvement in the left wall impingement
was the lower impingement height of the LPDI injector compared to the specific values
of 5 and 10 MPa of the HPDI injectors in the right-hand side. Impingement of piston top
impingement started early with a higher injection pressure, overall impingement more
enhanced, and peak values more enhanced which took with 3 MPa. On the other hand,
this case examined the impact of injectional timing and the number of injections on
impingement. As injection timing advanced, the left side wall became more prominent,
while the right side wall's peak was at 180° BTDC from the two other data points at
240° and 210° BTDC. The split injection of the fuel reduced the left valve impingement
by almost 50%; similarly it reduced peak impingement on the piston top by about 22%
compared to the single injection. The insights from this experimenting are that the
provision of optimising fuel injector settings are highly essential for better engine
performance and emissions regulation. Given below is fig 11[6].
5. Study on the effect of injection strategy
on the combustion and emission
characteristics of direct injection spark
ignition bio-butanol engine[7]
This review of literature concentrates on the probability that various alcoholic fuels,
especially n-butanol, may become substitutes for the fossil fuel used in internal
combustion engines. Researches prove that blends with alcohol have a higher rate of
combustion and emission of products of low grade than pure gasoline. This causes
several issues relating to atomization and volatility which can have effects on
performance and emissions of engines. The research reveals that getting the perfect fuel
injection strategy like increasing the pressure of the injection, and adjusting the timing
to have better air-fuel mixture efficiency can help n-butanol to prevent bad body
reaction. There have been studies on the experimental and numerical simulations to
scrutinize combustion and emissions of fuel injection pressure and time to add a likely
understanding for an improved combustion with n-butanol fuel. Moreover, there is still
the fact that there is still little knowledge of the best use of n-butanol as a renewable
energy source for internal combustion engines, and this is an area that needs further
study.
5.1 Methodology
In this study, a 3D Computational Fluid Dynamics (CFD) model is used to assess the
combustion behavior of pure n-butanol injected into a four-cylinder Direct Injection
Spark Ignition (DISI) engine under full-load optimal settings revealed that the bi-fuel
configuration was able to maintain the efficiency of the conventional gasoline-based
configuration. The combustion chamber has an exhaust gas turbochargered air intake,
with a wall-guide mixture formation method and concave piston top. Values like
injection pressure and fuel injection timing and so on as operating engine parameters
are indicated. The investigated physical model is based on RNG k-ε scheme for the flow
field, KH-RT model for droplets film and particles breakup, and Bai-Gosman model for
droplets-wall interaction. The O'Rourke turbulent dispersion model is used to track
falling droplets during turbulent flow, while a multi-component evaporation model
makes it possible to know the evaporation of droplets.
O'Rourke impact model for droplet crashing and SAGE precise chemical reaction
kinetics model for the general chemical action are the coped methods. Grid
independence is sought through the means of a grid refinement technique. In validating
the model's predictive capability through a comparison with experiment observation, the
simulation output matches real world data of combustion of n-butanol as shown in this
figure.
5.2 Model Validation
The study employs a procedure of adapting a model of a engine, wherein the work of the
process is simulated by spray of butanol and introduction of in-cylinder combustion
pressure. Proper spray calibration is important since the shape of a spray and the depth
to which it penetrates are taken into account. The calibration process is performed using
a pneumatic fuel injection system and a Photron SA1.1 high-speed camera according to
the spray imaging technique. With digital image processing, the insight into the
penetration distance will be thorough. The same experiment can be performed in
different chambers, with constant volume under varying temperature and pressure
conditions. The accuracy assured by this harmonization facilitates the spray calibration
in-cylinder. A proof of the spray model's accuracy is the fact that the research findings
with run and experiment coincide as far as the distance of penetration and shape of the
spray are concerned. Combustion model used at the previous test bench and published is
validated with experimental data during this test too, meaning there is a little
divergence in pressures measured in the combustion chamber.
5.3 Results of Study
The aim of the study is to evaluate the role of injection mode on the flow patterns,
combustion characteristics and emissions coming from an engine that is natural
gasoline n-butanol fuelled. The outcomes may indicate that injection time is a major
factor affecting the interaction between the spray-plume and the induct air flow, and
thus it can result in diverse flow field in-cylinder. Delaying the exact start time of the
spray will over time gradually rotate the spray plume direction in favor of the direct
inflow vector. This way it becomes easier at the intake open the spray across the whole
cylinder and less turbulent motion is generated. Promoting the injection timing provides
higher tumbling rate affecting to the mixture size. More than just along with the
increased crash pressures, they exacerbate the above effects with greater spray
momentum contributing to the decline of intake tumble and even allow negative tumble
ratio at certain timings.
The simulation also indicates that the ignition timing and pressure have also a
significant impact on the speed distribution the speed vector and the O/F value. Ignition
delay is decreased due to increased speed of flow field on injection timing that is
postponed which ultimately is used to create flames through forming the seeds of
flames. The business end close to spark plug operation is influenced by the tumble in the
cylinder in-line with higher pressure and delayed timings as it leads to under-tumble
denser mixtures.
Suggesting the amount of liquid film, the study shows that raising injection pressure
actually causes more liquid coating on the walls of the cyinder, unlike the tendency
observed with highly volatile fuels. The mentioned fact is that n-butanol has higher
viscosity and surface tension which obstruct droplet breakup and increase the possibility
of droplet back-splash.
In principle, the experiment demonstrated the interlinkage between injection energy,
in-cylinder flow, air-fuel-mixing process and combustion attributes. It estimates the
significance of fine-tuning the injection strategies to improve fuel-air mixture,
combustion efficiency and emission dispersion of the engine operating with butanol in
fuel.
6. Results and discussion for spray
impingement in DISI engines
6.1 Spray breakup model validation for CFD [1]
The spray breakup model was validated by comparing simulation and experimental
results for spray tip penetration and SMD in a DISI gasoline engine. Increasing
injection pressure led to higher tip penetration, with simulations matching experimental
trends. SMD increased with distance from the nozzle, noticeable at low injection
pressures. At high pressures, SMD values were consistent across distances, but trends
were accurately predicted.
6.2 Effects of injection pressure on the spray
development[1]
The injection pressure analysis, undertaken as part of this study, yields a number of
important conclusions. The first phenomenon concerns pressure rise. Certainly, as a
pressure increase, the duration of injection decrease drastically, by 30% reduction when
the pressure is 50MPa to 5.0MPa, irrespective of the injection quantity. This is because
of a clipped injection pulse, called a square wave, by DISI gasoline injector. Additionally,
pressure at the final injection phase is significantly lower than the pressure at the start.
Injection pressure is the route pressure that pushes the injected fluid into the pulse
injection chamber; it is dependent on the input voltage applied to the pump unit. Heavy
sprayed falls occur due to the greater pressure, with the fall droplet size more reduced.
To third, sweeping spray angle increases with the pressure of injection, but the pacing of
this high pressure decrease. Last, close-in last drop ejection at the end of travel is
similar across various pressures, though if the system is at low altitude and under high
loads the drop will be less penetrated due to the increased drag time.
Final pictures of nozzle development and final strain sprays show that the penetration
power of a spray tip is not determined by the injection pressure, but the spray cone
angles are more emphasized due to the increased turbulent kinetic energy as pressure
also increases. At the air point of nozzles, the spray flow is oscillating going to the each
nozzle hole, thus occupying less space during the low pressure, while increasing not only
when the pressure is rising but also wind resistance and air injection, extending the
covers of spray. Whereas water droplets in vertical spray plumes undergo more intense
thorough mixing with the surrounding air, they have a greater contribution to spray
expansion.
Basically, step pressure affects spray features relating to neck depth, cone angle, as well
as coverage area. As a result of this, the fuel distribution across the cylinder surface and
the intensive wall-impingement that takes place in practical use conditions is also
subject to a change.
6.3 Wall impingement[1]
As it is shown in the Fig.below[1] , a few different injecting timing variations in a low
speed, and middle load processes are seen under impinge wall conditions with spray by
two images. During the intake stroke the total impacted fuel moves to the piston as the
injection timing is advanced and this amount function is increasing linearly during the
injection period. In keeping with a later spray impact on the piston following a higher
first piston position is propagated due to an early injection. The initial amount of the
fuel sprayed is larger than the quantity, which works around slow piston velocity and
constant spray injection timing. In contrast, the case of late injection and above the
compression stroke the impinged fuel rises proportional to the piston's postion height for
advanced injection time.
The primary injector opens during intake stroke, with piston and chunk hitting the wall
at the same time, the piston speed, and the quality of spray being the determinants of
such problems. The lower the speed and injection range (load), the smaller the injection
pressure effect on wall impingement because the limited volume of spray in the cylinder
and small piston displacement during injection result in the small size of the spray.
changing of injection pressure don't have a noticeable effect except for waves of 5.0 MPa
at 1/4 intake stroke. For the case of injection during compression stroke, high pressures
decrease the amount of time the piston displacement is sustained and impingement with
the nozzle is kept to the minimum. The throttle and engine speed significantly influence
wall impingement as the tip penetration which indicates the location of the spray is
different when compared with different speeds or loads.
6.4 Conclusions
The research was designed to find out the force of jet strategies at the intake port of a
Gasoline DISI engine. The results obtained from the study can be summarized as
follows:The results obtained from the study can be summarized as follows:
1.With the pressure increasing, the injection timing is shorter and the spray cone angle
and spray area grow .There is no difference in the penetration if the sprays at the end of
injection are continuous towards the target area whether it is at low or high-injection
pressures.
2.Reserved positioning of the fuel injected is pronounced for the positions that otherwise
are early injection and late injection. Injection amount of impinged fuel increases with
the increase in injection pressure wherein the injected fuel will have in the
early-injection conditions, however, it will decrease with the injection pressure in the
late-injection conditions.
3. Along with the much improved fuel heating, the area where the injected gas wall
impinge clearly also expanded. The higher the speed of engine, advancement speed of
the injection timing at the wall impingement point would be also. Consequently, the
increase in the injection pressure made it possible to utilize the timing that covers a
wider range of the evaporation caused by superior atomization, which means fast and
wide spreading in an engine.
4. Atomization promotion is achieved at increasing fuel injection pressure thus, causing
the extending of the effective Weber range in the initial injection case. For retarded
times of injection, droplets are impact the walls of the nozzle in which they have already
lost their momentum, and the difference between the injection pressures that drop into
spray is negligible.
7. References
1. Junkyu Park , Taehoon Kim ,2018. Prediction of wall impingement in a direct
injection spark ignition engine by analyzing spray images for high-pressure
injection up to 50 MPa, Hanyang University, Fuel Processing Technology,Volume
179
2. Jingeun Song , Taehoon Kim, 2015. Effects of the injection strategy on the
mixture formation and combustion characteristics in a DISI (direct injection
spark ignition) optical engine, Hanyang University ,International Journal of
Heat and Fluid Flow,Volume 93, Part 2.
3. Sanghoon Lee , Sungwook Park ,2014. Experimental study on spray break-up
and atomization processes from GDI injector using high injection pressure up to
30 MPa,Hanyang University, International Journal of Heat and Fluid Flow,
Volume 45.
4. Junkyu Park, Taehoon Kim, 2018. Research Institute of Industrial Science,
Development of Methodology for Spray Impingement Solution , Hanyang Fuel
Processing Technology ,Volume 179
5. Essam Abo-Serie, Manolis Gavaises, 2003. Spray/wall interaction in
direct-injection spark ignition engines equipped with multi-hole injectors, City
University London.
6. Mayank Mittal,David L. S. Hung , 2010. Fuel spray visualization and its
impingement analysis on in-cylinder surfaces in a direct-injection, Journal of
Visualization
7. Zengbin Liu , Xudong Zhen,2014. Study on the effect of injection strategy on the
combustion and emission characteristics of direct injection spark ignition
bio-butanol engine, Energy, Volume 289
8. Aleiferis PG, Malcolm JS, Todd AR, Cairns A, Hoffmann H (2008) An optical
study of spray development and combustion of ethanol, iso-octane and gasoline
blends in a DISI engine. SAE Paper 2008-01-0073
9. Cronhjort A, Wahlin F (2004) Segmentation algorithm for diesel spray image
analysis. Appl Opt 43(32):5971–5980. Doi: 10.1364/AO.43.005971
10. Grimaldi CN, Postriot L, Stan C, Troger R (2000) Analysis method for the spray
characteristics of a GDI system with high pressure modulation. SAE Paper
2000-01-1043
11. Hennessey R, Fuentes A, Wicker R (2001) Effect of injection timing on piston
surface fuel impingement and vaporization in direct-injection spark-ignition
engines. SAE Paper 2001-01-2025
12. Baretzky U, Andor T, Diel, H and Ullrich W 2002 SAE 2002-013357 [6]
Stanglmaier R H, Li J and Matthews R D 1999 SAE 1999-01-0502 [7] Miller A L,
Ginter D, Seaba J P, Loyalka S K and Ghosh, T K 1998 IMechE, Vol. 212 Part D,
pp 525-532
13. Miller A L, Ginter D, Seaba J P, Loyalka S K and Ghosh, T K 1998 IMechE, Vol.
212 Part D, pp 525-532
14. Christian Rodrigues , Jorge Barata, 2012. Spray impingement modelling:
Evaluation of the dissipative energy loss and influence of an enhanced near-wall
treatment , University of Beira Interior, Covilhã 6200‐001, Portugal
15. P.J. O'Rourke ,Statistical properties and numerical implementation of a model for
droplet dispersion in a turbulent gas J. Comput. Phys., 83 (1989), pp. 345-360
16. Sanghoon Lee , Sungwook Park ,2013.Experimental study on spray break-up and
atomization processes from GDI injector using high injection pressure up to 30
MPa, Graduate School of Hanyang University, Seoul 133791, Republic of Korea,
Volume 45, February 2014, Pages 14-22
17. F. Schulz,W. Samenfink , 2016. Systematic LIF fuel wall film investigation, ,
Volume 172, Pages 284-292
18. Hanzhengnan Yu, Xingyu Liang,2016. Experimental investigation on wall film
ratio of diesel, butanol/diesel, DME/diesel and gasoline/diesel blended fuels
during the spray wall impingement process, Fuel Processing Technology
Volume 156, Pages 9-18
19. Christian Rodrigues, Jorge Barata, Spray impingement modelling: Evaluation of
the dissipative energy loss and influence of an enhanced near-wall treatment,
Fuel Processing Technology, Volume 107,Pages 71-80
20. Miguel R. Oliveira Panão, António Luis N. Moreira, Statistical analysis of spray
impact to assess fuel mixture preparation in IC engines, Fuel Processing
Technology, Volume 107, Pages 64-70
21. Matsui, Y. and Sugihara, K. "Sources of hydrocarbon emissions from a small
direct injection diesel engines", JSAE Review, Vol.7, pp.4-11, 1986.
22. Fujimoto, J., Senda, J., Nagae, M. and Hashimoto, A. "Characteristics of a diesel
spray impinging on a flat wall" , International Symposium COMODIA Vol. 90,
pp. 193-198,1990
23. Kat sura, N., Saito, M., Senda, J. and Fuji-moto, H. "Characteristics of a diesel
spray impinging on a flat wall", SAE Paper No. 890264,1989.
24. Miraz, R. "Studies of diesel spray interacting with cross-flow and solid
boundaries," PhD thesis, University of Manchester, Faculty of Technology, 1991.
25. Sakane, A., Hamamoto, Y. and Sumimoto, T. "Behaviour of diesel spray
impinging on a wall", J . Mech. Eng . Soc. Japan , Vol. 54, pp.1861-1865, 1988.
26. Saito, A., Kawamura, K., Watanabe, S., Taka-hashi, T. and Naoyuki, T. "Analysis
of impinging spray characteristics under high-pressure fuel injection (1st report,
measurements of impinging spray characteristics)", Trans. Jap. Soc. Mech.
Engrs. B, Vol. 59, pp. 3290-3295, 1993.
27. Naber, J. D. and Reitz, R. D. "Modelling engine spray /wall impingement." SAE.
Paper 880107, 1988.
28. Naber, J. D., Enright, B. and Farrell, P., "Fuel impingement in a direct injection
Diesel engine", SAE Paper 881316, 1988
29. Alloca, L., Amato, U., Bertoli, C. and Corcione, F. E. "Comparison of models and
experiments for diesel fuel sprays". In Int. Symp.on Diagnostics and Modelling of
Combustion in I C Engines, pp. 225-261, 1990.
30. Watkins, A. P. and Wang, D. M. "A new model for diesel spray impaction on walls
and comparison with experiment", In Int. Symp.on Diagnostics and Modelling of
Combustion in I C Engines , Kyoto, pp. 243-248, 1990.
31. Hung DLS, Chmiel DM, Markle LE (2003) Application of an imaging-based
diagnostic technique to quantify the fuel spray variations in a direct-injection
spark-ignition engine. SAE Paper 2003-01-0062
32. Hung DLS, Zhu G, Winkelman JR, Stuecken T, Schock H, Fedewa A (2007) A
high speed flow visualization study of fuel spray pattern effect on mixture
formation in a low pressure direct injection gasoline engine. SAE Paper
2007-01-1411
33. Kawajiri K, Yonezawa T, Ohuchi H, Sumida M, Katashiba H (2002) Study of
interaction between spray and air motion, and spray wall impingement. SAE
Paper 2002-01-0836
34. Mittal M, Schock HJ (2010) A study of cycle-to-cycle variations and the influence
of charge motion control on in-cylinder flow in an I.C. engine. ASME J Fluids
Eng, 132(5):1–8, 051107
35. Mittal M, Zhu G, Stuecken T, Schock H (2009) Effects of pre-injection on
combustion characteristics of a single cylinder diesel engine. In: Proceedings of
the ASME international mechanical engineering congress and exposition, Paper
IMECE 2009
36. Mittal M, Hung DLS, Zhu G, Schock H (2010) A study of fuel impingement
analysis on in-cylinder surfaces in a direct-injection spark-ignition engine with
gasoline and ethanol-gasoline blended fuels. SAE Powertrains, Fuels and
Lubricants Meeting, Paper No. 2010-01-2153
37. Stow, C. D. and Hadfield, M. G. "An experimental investigation of fluid flow
resulting from the impact of of a water drop with an unyielding dry surface",
Proc. R. Soc. Lond.-A ,Vol. 373, pp. 419-441, 198
38. LPark J, Xie X, Im KS, Kim H, Lai MC, Yang J, Han Z, Anderson RW (1999)
Characteristics of direct-injection gasoline spray wall impingement at elevated
temperature conditions. SAE Paper 1999-01-3662
39. Mutchler, C. K., "The size, travel and composition of droplets formed by
waterdrop splash on thin water layers" Ph. D Thesis, University of Minnuesota,
1970.
40. Matsumoto, S. and Saito, S., "On the mechanism of suspension of particles in
horizontal conveying: Monte Carlo simulation based on the irregular bouncing
model", J. Chem. Engng. Japan , Vol 3, pp. 83-92, 1970.
41. Ghadiri, H. "Raindrop impact, soil splash and cratering", Ph. D Thesis,
University of Reading, 1978.
42. Wright, A. C. "A physically-based model of the dispersion of splash droplets
ejected from a water drop impact" , Earth Surface Processes and Landforms , Vol.
11, pp. 351-367, 1986.
43. A.M. Worthington, On the forms assumed by drops of liquids falling vertically on
a horizontal plate, Proceedings of the Royal Society of London. Series A:
Mathematical and Physical Sciences 25 (1876) 261–271.
44. A.M. Worthington, A second paper on the forms assumed by drops of liquids
falling vertically, Proceedings of the Royal Society of London. Series A:
Mathematical and Physical Sciences 25 (1877) 498–503.
45. J.D. Naber, R.D. Reitz, Modelling engine spray/wall impingement, SAE Paper,
1988.
46. A.A. Amsden, P.J. Orourke, T.D. Butler, KIVA-2: A Computer Program for
Chemically Reactive Flows with Sprays, , 1989.
47. J. Senda, M. Kobayasshi, S. Iwashita, H. Fujimoto, A. Utsunomiya, M.
Wakatabe, Modelling diesel spray wall impingement on a flat wall, SAE Paper,
1994.
48. L.H. Wachters, N.A.J. Westerling, Heat transfer from a hot wall to impinging
water drops in spheroidal state, Chemical Engineering Science 21 (1966)
1047–1056.
49. M. Nagaoka, H. Kawazoe, N. Nomura, Modelling fuel spray impingement on a
hot wall for gasoline engines, SAE Paper, 1994.
50. C.X. Bai, A.D. Gosman, Development of a methodology for spray impingement
simulation, SAE Paper, 1995.
51. C.X. Bai, H. Rusche, A.D. Gosman, Modeling of gasoline spray impingement,
Atomization and Sprays 12 (2002) 1–28.
52. G.E. Cossali, M. Marengo, A. Coghe, S. Zhdanov, The role of time in single drop
splash on thin film, Experiments in Fluids 36 (2004) 888–900.
53. R.L. Vander Wal, G.M. Berger, S.D. Mozes, Droplets splashing upon films of the
same fluid of various depths, Experiments in Fluids 40 (2006) 33–52.
54. J. Liu, H. Vu, S.S. Yoon, R.A. Jepsen, G. Aguilar, Splashing phenomena during
liquid droplet impact, Atomization and Sprays 20 (2010) 297–310.
55. S. Chandra, C.T. Avedisian, On the collision of a droplet with a solid-surface,
Proceedings of the Royal Society of London. Series A: Mathematical and Physical
Sciences 432 (1991) 13–41.
56. M. Pasandideh-Fard, Y.M. Qiao, S. Chandra, J. Mostaghimi, Capillary effects
during droplet impact on a solid surface, Physics of Fluids 8 (1996) 650–659.
57. C. Arcoumanis, D.S. Whitelaw, J.H. Withelaw, Gasoline injection against surface
and films, Atomization and Sprays 7 (1997) 437–456.
58. G.E. Cossali, A. Coghe, M. Marengo, The impact of a single drop on a wetted
solid surface, Experiments in Fluids 22 (1997) 463–472.
59. A. Silva, J. Barata, C. Rodrigues, Influence of spread/splash transition criteria
on the spray impingement modelling, in: ILASS - Europe, 2011, pp. 1–10.
60. Chen Z, Wang L, Zhang Q, Zhang X, Yang B, Zeng K. Effects of spark timing and
methanol addition on combustion characteristics and emissions of dual-fuel
engine fuelled with natural gas and methanol under lean-burn condition. Energy
Convers Manag 2019;181:519–27
61. Erdiwansyah MR, Sani MSM, Sudhakar K, Kadarohman A, Sardjono RE. An
overview of Higher alcohol and biodiesel as alternative fuels in engines. Energy
Rep 2019;5:467–79.
62. Huang Y, Surawski NC, Zhuang Y, Zhou JL, Hong G. Dual injection: an effective
and efficient technology to use renewable fuels in spark ignition engines. Renew
Sustain Energy Rev 2021;143:110921.
63. Wang L, Hong C, Li X, Yang Z, Guo S, Li Q. Review on blended hydrogen-fuel
internal combustion engines: a case study for China. Energy Rep 2022;8:6480–98.
64. Tian Z, Wang Y, Zhen X, Liu Z. The effect of methanol production and application
in internal combustion engines on emissions in the context of carbon neutrality: a
review. Fuel 2022;320:123902.
65. Chen Z, He J, Chen H, Geng L, Zhang P. Comparative study on the combustion
and emissions of dual-fuel common rail engines fueled with diesel/methanol,
diesel/ ethanol, and diesel/n-butanol. Fuel 2021;304:121360.
66. Zhen X, Wang Y, Liu D. Bio-butanol as a new generation of clean alternative fuel
for SI (spark ignition) and CI (compression ignition) engines. Renew Energy
2020;147: 2494–521.
67. Sarıkoç S. Effect of H2 addition to methanol-gasoline blend on an SI engine at
various lambda values and engine loads: a case of performance, combustion, and
emission characteristics. Fuel 2021:297.