Realistic Common Niagara and particles
Hello, this is Hyunsang Park
In this Unreal VFX
we will get to know about Niagara effect system
Niagara is a particle system of Unreal
which is an upgraded system from cascade
Technical artists use Niagara
to generate additional functions
without the help of programmers
in this Niagara system
there are various modules
that can control colors and movements
Explaining them all would be difficult
but through examples
I have constructed the lecture focusing
on the main features
First, in the first lecture of Unreal VFX
we will learn about Niagara and particle
Niagara is an asset that makes various visual effects
using the format of particle
This particle system
has the characteristic of being controlled according to time
In this lecture we will learn
how to attract the users' attention
through the fancy movements and color changes of the particle
Concept of Niagara
Before we get into the lecture
let's first learn about the project settings
You will normally choose Third Person
from this Game category
and make sure it contains
blueprint and stater content
Then name the project
and click on the Create button
Even if you already
created a project without
a starter content on Third Person
you can click on the Add button from the content browser
and select the Add Feature or
Content Pack
Then you can add the needed
starter content from Content
and Third person from Blueprint
So these two
we will start off from this form of project
with starter content and third person for the remaining lectures
What you will learn through this lecture
is an asset called Niagara
Niagara is an asset
provided by Unreal Engine that creates effect
Basically effect refers to
if a person is walking on sand
there will be dust
Similarly, if you light something in fire or use magic
there will be sparks
Or if a bullet hits a wall
then there will be smoke and debris
It is an asset suitable for these things
It doesn't just show
the animations on the UI
according to the users' action
it rather does the visual reaction
to the users' action
Niagara has various options
like changing colors or creating movements
There are such features
and there are again composed with
various options or parameters
Of course professional effectors will
be able to make use of every single one of these
but if you're not one
it is one of the fields that are very difficult to study
So what I recommend is
through marketplace
you get Niagara asset or
other effect assets
and edit them and then use it
Also you could use the asset as is
but changing different options little by little
to modify it to your liking
will be a good way of learning
In terms of learning Niagara
when you search things up on
the internet
or in marketplaces, actors
You can search VFX or effect
or the original name of the asset
Niagara
Also these effects itself
are usually composed of small grains
called particles
so they are usually called particle effect or particle system
Not only in Unreal but in most 3D or 2D
these particle systems for special effects
have their own system
Before Niagara
Unreal used a system called Cascade
Ultimately, Niagara and Cascade are both
assets to express small grains called particles
Especially everything that's provided by starter content
is Cascade
But compared to Cascade
Niagara is way more advanced
and has many features that can not only edit modules
but also expand them
So it's a much better system to create
interaction that has animation data
and blueprint data connected
When you look at these assets
in starter content particles
you will see this P_Fire, let's click on that
It says Cascade here
Double click, and you see a very old UI
It's the UI used in Unreal 4 and even 3
You can see this fire effect
and also smoke and tiny sparks
On the right, there are various settings
called Emitter
That is where
each of the modules are
And there are many options
for each of them in the detail window
But you'll be able to spot some characteristics
Even though they are the same features
the orders are different, like this one has location on the top
this one has size here
and velocity or initialize option is on the bottom
with other things in the middle
Like this, the order
are all different
This can be a disadvantage of Cascade
It does work even though
the orders are all over the place
and everything everywhere
but it could be a little difficult if you're to
edit this when this is someone else's work
These information are more organized
in terms of orders in Niagara
which helps you understand
these assets easier
We'll then learn how this particle system
regardless of Niagara or Cascade
how it generally works
This Flame window
that you see over here
is what we call the Emitter
and the more detailed parts in the Emitter
are what's called modules
If could be Require module, Spawn module
or Initial Size
All these are modules
These modules eventually
are used to control the movements of the particles
What's unique here are
the ones like Lifetime
Not only Niagara but most particle systems
in any software all are affected greatly
by lifetime, time
and there is something you must remember
For Static Mesh that we generally use
3D Static Mesh
or Skeletal Mesh for animation
once there is level allocated to it
it remains until we request for
particular deletion
This goes the same for other actors like Light
or else, so not just 3D objects
But on the other hand, these particle systems
have predetermined lifetime
We call this Lifetime
and this refers to
the lifetime of each particle, each small grain
So when it comes to particle control
controlling the time well
is a very important factor in creating good effect
To give you a brief explanation on the structure
particle systems
like Niagara or cascade
they are all types of particle systems
and within these particle systems
there are various Emitters
And in each of these Emitters
there are various modules
But it's difficult to understand
unfamiliar concepts
so I use the metaphor of factories for particle systems
but this factory does not manufacture
industrial goods like desks or computers
it makes fresh food that has shelf life
So Lifetime would be the shelf life
It's a fresh food factory
and in the manufacturing lines of this factory
for example milk
there will be lines that make white milk
and others that make chocolate flavored ones
or strawberry flavored ones
You can think of Emitters as each of those lines
and what composes the ingredients and mixes them
and packaging are all managed by
the modules of the Emitters
So at the end, we create particles
So when you learn particle
you can think of the particle system as a factory that makes fresh food
that has shelf life
and through the Emitters we can make
various fresh food, products
and you can remember those foods
as what we call the particles
I think this will help you understand
this system that you might feel unfamiliar
Niagara effect production
Let's first make Niagara
Create a new folder on the Content folder
A VFX folder
And here, click on the Add button or
right click on the blank space on the right
and select Niagara system
We would usually
select from all these presets or templates
and begin from that
but also on the very bottom
there is Create Empty Niagara System
When you click on that, you can create
an empty Niagara system
Let me name this Niagara system
VFX_Fire
We're going to make fire
I'll open the editor by double clicking the asset
On Niagara editor, there are three big parts
of the screen
First, preview is a window where
you can see the movement or shape of the particle
and under that is the window
with the options for various parameters
And on this graph window
you can add Emitters
or modules
Timeline under that shows
how the particles move with time
and also is used to control the speed
When you choose each of the modules
you can choose
from various options
on the detail window on the right
I will explain about the menu bar
on the top later on according to the features needed
Now let's right click on the graph window
and click on Add Emitter
Then you'll see
the template window
that we saw when we were making the Niagara asset
From the various templates on Niagara
there is Empty Emitter
It's an Emitter without anything right now
Let's click on this and click the Add button
Then on the very right, a blue node
This blue node shows the user's parameter
or the module window for the whole Niagara system
There's the Emitter window and on the right
there are various modules in brown that
let's us make movements or each sparks
How the effect shows will differ little bit
but similar to cascade, we will
place these various Emitters in this particle system
to crate one effect
so remembering this structure
will help you adapt quickly into Unreal, Unity
or other situations as well
Also in Niagara
there is this additional feature
where you can manage separate Emitters
So after you add a Niagara Emitter on FX
with the add asset button
let's also do Create Empty Niagara Emitter
like this
Name it VFX_Emitter_Fire
and you can also put it in a different Niagara system
Of course this Emitter won't
show anything now
but eventually like this
Niagara will control these Emitters
through the Niagara system
and that these Emitters can
exist as independent assets
That's what you'll have to remember
This Emitter that I made for explanation
I will select and click on delete to remove it
If you look at the Emitter here
there is this update area
Spawn area, Particle Update area
The areas of Emitter is clearly separated
unlike Cascade
and Emitter update literally means
the factory setting
For example the production life that
produce 10 per a minute
It's the area that does those factory setting
and Particle Spawn and Update, put simply
are the product settings
Will it be white milk, or chocolate flavored milk
So the areas that control the Emitter are
largely separated into factory setting area and product setting area
and each items in those
are what we call modules
You can also add different things
to this module by clicking on the plus button
Those we will work on later on
and first, if we made an asset
we must name it
So we'll right click on the name area
and rename it
It goes the same on the detail window here
You can change the name by double clicking
We'll change the name from Empty
to Fire
The name is especially important later on when
we export these modules
that are made
We can export these Emitters
so if you change the name in advance
you will be able to export the Emitter modules you want
and use them
First let's learn the characteristics
of Fire that we're going to create
It's not just a still image
but a moving video
of a flame, then we could think of
flames lighting up like this
These movements of the flame
or how it dies off and such
Looking at the changes
and sketching them out
helps a lot to think about
how you'll change the shape of it
So to explain some properties of flame
first it keeps on moving
It sways with wind
It also separates and vanishes
For now in my drawing
it's in green
but usually they are red
especially on the outer layers
and towards the middle
it has orange or bright yellow colors
Another property of fire is
that it has a rough range
A flame of this size won't get much bigger
unless it catches on some other object
Of course there will be some changes as it waves
but roughly it will stay within
a certain range
It also has the shape of
being wider on the bottom where it starts
and getting narrower as it goes up
So to simplify these it will look like this
It goes from bottom to up
and changing colors from bright yellow to red
Having a certain range
but also getting narrower as it goes up within the range
We will break down these properties
and create each of them
Before you create the effect
knowing the properties of what you're trying to create
is very important
in terms of expression
First, Emitter Update
Emitter Update
Like I mentioned, if this whole thing is a factory
Emitter is a production line
For production lines, how much production there is in a day
is very important
and just like that, we can also set how many will be created per second
Click on the Emitter Update Plus button
and add Spawn Rate
Then we'll add 30 for the Spawn Rate value
If we put 30 here
as you can see on the preview window
There are round particles
but it looks like one
This is numerous particles
layered on top of each other
If you activate the particle counts
on show here
you will be able to see the particle amount
in numbers like on my screen
that are in the preview window
So we have made the particle generate
30 per second through the Rate value
It's creating 30 particle per second
but the total particle count says 150
So the number of particle actually created are 150
Where this 150 comes from is
from the Emitter State right above it
Emitter State means the running time of the production line
and Spawn Rate refers to the production amount
The factory needs to determine the running time
and if you select Emitter State
the Life Cycle Mode
is on system and not on self
This means that I don't manage it one by one
but that it will follow the factory's default setting
and the factory's setting says
the Loop Duration is 5 seconds
All these time mentioned here
are in seconds
The repetition of Loop behavior
is set as infinite
It produces for 5 seconds and re-runs every 5 seconds
So in creating particle
the Emitter Update area here
plays a very important role
Of course there is the Rate method
which has fixed per second production
there is also Burst that creates
tens of thousands at once
which is another method
You can choose
according to what you want
and for now
we'll work with the Rate method that creates
certain amount every second
Now we'll create particle motility
Now the particle is still
but it must move up for it to look like flames
To do that, at first
to let it move at a persistent speed
you can click on plus on the Spawn area
and click on Add Velocity
We are setting the speed
Here it shows an alert on the detail window
and you'll see Fix issue buttons
Before, on Cascade
even if the modules didn't match each other
there wasn't a way to know
But on Niagara, if there's a problem
or modules missing
it reports the error and
tells you what's wrong
What we're adding here is
the first item, Solve Forces And Velocity
Click on Fix issue here
and the error will be solved as you can see
and additionally we didn't add it here
but with Fix issue, you can see that
the Solve Forces And Velocity item is added
to the Update items
The speed that the particle moves up
is now set on 50 unit up
on Velocity
and you can change the speed
of how many units you want it to move per second
If we set the Z axis
the direction upwards as 100
then it shows that it's going up
towards the top of the screen
Let me change the view mode to Wireframe
from Lit
Then you can see on the screen that
these rectangles are going up
And you can also see that even if you see it from closer
or from the bottom by right clicking
that the squares are always facing me
We call this Billboard
Billboard means that it always faces the camera
without us having to set a rotation value
This object, this mesh, wherever it is
if there is a camera, it will always
face the camera and this type of asset
is called Billboard
So the way in which
the basic round image that we saw
being round images put into these squares
is the common way
of particles
This way, even when we have a lot of particles
we can create the image that we want relatively easily
Now back to Lit mode
let's put a color to them
Adding colors, from the beginning
on the Initial Particle item's detail window
you can set the color through color mode
and if you do Unset on Direct set
it means that there won't be anything designated to it when it starts
The default value is white
and if we change the color, it shows red
White, or green
like this change the color
but flames don't have just one color
Let me roughly mark the colors here
It starts off yellow
Then it proceeds to orange
and then it turns red and the very edges
This is how it's usually seen
Following the movement direction
having a gradient of color from the beginning point
to the end point
To do that, we must use the Update item
instead of Spawn
Spawn here is the initial, default value
and this is the changing value
The change could be that of colors
or that of direction, speed
and many other things
So as time passes and it goes up
the color should change so to do that
click on the plus button on Particle Update
and add Scale Color
Scale Mode on Scale Color
is a method to express the
changing aspects
The simplest form
would be changing the RGBA Linear Color Curve
and you'll see the numbers
turning into a Gradient Map
that is visualized
So let's express the colors here
What above is you can see when you double click that it chooses the color
and below is alpha, so transparency
Let's start from the color first
From bright yellow, our end point is
changing it to red
Click on Ok and on the very top
it looks like a light saber
but the yellow particles
change into red
But generally when creating flames
there are other colors commonly used
so let me explain a little more about them
Between yellow and red
and it shows when you click on it
We usually use orange here
Let's drag the red a little more
And it does not end at red
but let's click one more time on the edge
to add and double click
to end off with a dark brickish color
So a total of four colors
Bright yellow, orange, red, dark red
We have four levels of colors
but these are colors that I randomly picked
bur rather these are the common color combination
used in particle examples
The reason why it's getting blurry as it goes up
is because of the transparency here
The background not showing
can be solved by clicking on Show Environment
on the preview setting window to see how it looks on a bright environment
and another thing, the transparency
you can check how it's managed
If you want to control the transparency
with a little more detail
you can do this
This is also a common combination
of alpha values
It's not ideal if we can visibly see the particle
being generated at the starting point
so we usually set the alpha value as 0
Then it goes immediately to 100%, 1
you can double click on it
And closer to the middle
also double click on the semitransparent value
and set this as 1 as well
Now you can see, unlike colors
the colors are relatively evenly distributed
while alpha values are more
extreme in its values
These settings are used a lot
in other particles as well
So it would be nice if you keep this in mind
You can also control how much it shows by
dragging the location like this
So eventually we have this particle
going upward and as it goes up
the colors changes little by little
Now, the movement of the particle itself
in terms of color seems similar
to a candle light or a flame
but the movement is too uniform just going up
so the movement is very awkward
So let's set the range it moves in
and create the details
First click on plus on Particle Spawn
and click on Shape Location
Then it says Sphere by default
As you can see each particle grains
are moving upward in a bit wider range, scattered around
This can be managed by changing the Sphere's radius
as we change it from the default value 100 to 0
it shows the same movement from what we initially had
but as we widen this
Let me make it even wider than 100
Then you can see like this
the range has widened and in the virtual space called Sphere
it is Spawned randomly
so it goes up scattered like this
but if this is too wide
or moves completely randomly, that would be a problem
so we must control it to an appropriate size
Let's change the Primitive type to Cylinder
and narrow the range a little
Height value 10
and radius at 30
Then compared to the straight movement
it looks a little more like a flame
It changed a little
And there are some texture on the edges
adding to the shape
making it closer to a flame than before
Basically cylinder
is a circular tube
so the particles are randomly generated within that range
Take a look at initial Particle
and you'll see the lifetime is 5
You can think of this as the shelf life
Each particles have the lifetime of 5 seconds
and are spawned
If we change this to 50
then it is given the lifetime of 50 seconds
so it goes way higher up
But the reason it doesn't look red is
because before it turns red
the particle generation is over in the timeline
and let's turn this back to the default value 5
Going towards the bottom here
you can see Sprite Attributes among the things
that set the particle settings
The Renderer that we're using now
What shows the drawing on the screen
uses Sprite Renderer
so on Initialize Particle here
you can use the options of Sprite Attribute
to set the particles' sizes or rotation
and edit them
Here, Mesh Attribute or Ribbon Attribute
will be affected if a separate Renderer is added
but even if we change these here
there is only Sprite Renderer
so these won't be affected
So go to Uniform on Sprite Size
and set the size as 10
then you can see that it's a little smaller now
And if we change it to 50
each particles are
way denser like this
But the particles only go up
and the range is very uniform, which makes it look awkward
So now we'll
make it get narrower as it goes up
by adding a module on the Update item
What was set at Initialize is the value when it begins
and Update means the change during the lifetime
We are using Sprite
so search Sprite here
then there is this module called Scale Sprite Size
We'll add this, a size module
Then the default value is small like this
and then the Scale goes from 0 to 100, 100%
It's set to go from 0 to 100%
and I'll just make the window larger so it's easier to see
So 0 here refers to the beginning point
when each particles start
and the X axis here is time
and 1 here
doesn't mean 1 second but 100%
We had our particles at initialize
set at 5 seconds
So here, 1 means
when 5 seconds pass from 0
so that 100% of time has passed
During that time, the change in Scale value
is expressed on the Y axis
So the X axis is time, and Y axis is value
Similarly on Scale Color
it was time passing as we go to the right
So in most particles, the horizontal, X axis
means time
These each values
These triangular shapes
are called key
This is about the time, X axis, and Scale value, Y axis
There are these two
So click on one point
and it shows X axis and Y axis
So right click here
and add key to add value
or you can drag it to change the value as well
If you change it like this, the change will be sudden
then slower after than
If you don't need it, right click and Delete
or use the Delete key on the keyboard
to remove Key values that you don't need
So let's change the graph shape a little
Add a key by clicking on Add Key
and we'll put that a little before where it reaches 100%
The max doesn't have to be 1
it could be twice as well
It's in scale, so it can be twice as big
When it goes out of the range of the graph
you can click on this zoom button
on the very left
to see the graph better
And make it come back to 0 at the end
Setting it to slowly get narrower
These tiny bubbles in the beginning
are kin of awkward, right?
So in the beginning, we can put about 0.7 to 0.8
so that they overlap and the movement looks like this
Let's set it like that
Now with these changes
to make it look a little smoother
you can right click and set the Key value as Auto
then the graph will turn into a curved shape
to make the expressions smoother
So with the handle you can also choose how
sloped the curve is
With these settings
it looks more like a flame
Let's put this in world
First save it
and drag the flame that we made onto world
and we can see the flame
The flame is vanishing towards the top, natural
If we change a value
For example on initialize Particle
we change the Lifetime to 3 seconds
then that is shown in world as well
Now let's use Material
to create a more detailed flame
Let's do that
Material used in particle
are also done using material editor
and connecting it to a Renderer
This time, let's make a Material
on the content browser
Then name the Material M_FireFX
and tap enter to open the Material Editor window
Usually the most basic setting of the Material Editor window
is set to be suitable for 3D object creation
We're going to change the settings a little bit
so that it suits effect better
First, let's change the Blend Mode from Opaque
Masked, Translucent, or 3D object
to Additive type
This characteristic, like Sprite that we previously saw
is what makes these semitransparent objects
look brighter as they are overlapping
with each other
Translucent things getting brighter and brighter as they overlap
Because particles
are emitting light, they are flames
It is to show that effect
and in addition to that, Shading Model as well
would not need to be affect by light
because it is lighting up by itself
So we'll change the Shading Model to Unlit
Then on the master node on the right
we can see that only Emissive Color and Opacity
are activated
Here, we're going to add a texture
with Texture Sample
Search Texture Sample
and there is a texture called simple
that is not in the default starter content
I'm going to provided this for you
to download it
and you'll just have to drag this texture file
into the content browser window
So select this texture
and connect it to the
Texture Sample node here
Then the texture is sent
Usually for 3D objects, we use it just like this
But for particle
you must add this thing called Particle Color
We had changed the color value
through modules
What delivers the changing color values
from the module to the Material is
this Particle Color module
so you must connect these two with Multiply
to bring the proper
color or transparency expressions
We have learned how to make
the most basic Particle Color
and now let's save this
and put it into Sprite Renderer
Select M_FireFX from content browser
and click on the arrow
Then the shape looks
a little more like a flame
If there were no Particle Node
Let's remove the Particle Color Node
If this was the case
no matter how much we change using the Scale Color
there is no change in color
So if you want to change particle color
through module
you must create a Particle Color Node
that can deliver the module's values
Now with the Material on the particle
compared to when we first started
Let me turn off the modules
I'll turn off Color, Shape, and Scale
then it looks like a light saber
but now with Scale and Color
it has become more like a flame
If we look at it closer for long
we used too simple structure of a particle
using texture to create it
so the particle's shape
seems a bit monotonous
So now we'll learn
how to solve this problem
We usually call this sequence texture
but the concepts might be a little difficult to understand from here on
Click right
and create Material
and name it M_FireFX_SubUV since
we're going to use the feature SubUV
Open the Material window and do the same as before
with Additive on Blend Mode
and Unlit for Shading Model
but when creating node, instead of Texture Sample
we'll search SubUV
and there is Particle SubUV
Select that, and it's the same for putting texture in
It's the same with general Texture Sample
But what's different is
You see the options are also very similar
I'll show you the differences a bit later on
For both of these
we'll select with Shift, and T_Fire_SubUV texture
This is a texture provided by starter content
Let's add that
So it's added to both of them
First, to SubUV, use Multiply
Let's move this Texture Sample away since it's just for explanation
We'll multiply the color values with
Particle Color Node
and also connect the alpha values
with Multiply as well
So RGB to Emissive, and Opacity to Opacity
Now looking at this on a flat surface
you can see that the texture is
planned out like a grid
Let's first save this
and on Renderer
we'll register the SubUV that we just made
instead of FireFX that uses a single image
First register the M_Fire_SubUV
then you'll see this very grid-like shape
with a weird texture
On the bottom here, there's this SubUV
and there's this item called image size
Let me show you the texture that we're going to use first
On the texture item on starter content
Let's go down
It's this T_Fire_SubUV texture
Double click on that
and it shows these many images
Six horizontally and six vertically, 36 images in total
are planned out in a grid
Generally texture
means showing this whole page
but SubUV divides the texture into n pieces
It cuts these all into n pieces
and make it look like they are just in one page
So if where we start is number 0
it will go to the right which is frame 5
then back to the very left of the next row
and go from frame 6 horizontally
and then back here, in a zigzag motion
It goes from frame to frame
almost like an animation
so when we're using SubUV
we must let the particle know
how many pages of images we're using
So the image size
we'll let it know that there are 6 horizontally and 6 vertically
then it will first show the first frame
which is the image on frame 0
And we must make this flow like an animation
from one frame to another
Over time, from frame 0 to frame 35
you need to go through a total of 36 frames
so we'll add SubUV Animation on
update, not Spawn
Add that and by default it's set to flow linearly
from the beginning to the end
and you can also set the beginning and end frame
What's important here is
what Renderer we're going to use
to make this animation
Click on Sprite Renderer
and select the Renderer
currently added to the Emitter
then you'll see the image flow like this
If this doesn't properly show up
you can try changing the Spawn Rate value to 1
to see the movements like this
Let me put it back to 30
There is an important reason
in using these features
Of course these days the effect systems are so good
so not only just having the Rate value at 30 or 300
but also like 3,000 is possible
Although it won't look pretty
you can scatter 3,000 particles even
But this causes a problem in real time engine
When what happens? When Particle count increases
Of course it deters the performance
But can we know how any particles
there are in a flame?
It will only be possible to create a flame
with countless amounts of particles
But in videography, this is commonly done
In the videography field, they put
crazy amounts of particles and render them for hours
to create a single complete flame image
but in real time we can't
use that many particles like in videos
so conversely, we pre-render
video tools, 3D tools and what is that?
These sequence textures
are pre-rendered
So the rendered results
are turned into sequence texture like these
Each and every one of them rendered
planned out to create a whole page
so that the detailed image using
millions of particle is somewhat depicted
So the lack of particles
compared to videography
is resolved by these sequence textures
After using sequence texture it might look
a bit awkward since there's too many overlapping
So you can adjust the value
according to the effect
Increase of decrease the spawn rate
to make the flame look a little more dynamic
That will also be another way
Like this, particle is
composed of very diverse modules
So through this lecture
I hope you got to understand
the Niagara system
In this lecture, we created a flame effect
to practice the main modules of the Niagara system
You might have felt this during the practice
but when using particle systems like Niagara
change and time are important
so please remember that you must think of these
when creating an effect
Then we'll wrap up this lecture by looking back at what we've learned
Thank you
Concept of Niagara
Niagara Effect provided by Unreal Engine Niagara is used for particle and Emitter production and uses time control option
Niagara effect production
Flame particle production Use Spawn Rate to set particles produced per second Use Emitter State to set particle production time
Motility production Add Velocity from Particle Spawn to make particle move up
Add SolveForcesAndVelocity module for speed or power
Color applicatoin Add Scale Color module to change color Use RGBA Linear Color Curve for color information
Adjust movement range Set default size on Particle Spawn and set production time, size, colors through Initial Particle
Use Scale Sprite Size to make the shape of flame that gets narrower towrds the top
Fire effect material produciton Set Blend Mode type as Additive so the property of becoming brighter as particles overlap is added
Add Texture Sample node and register T_Fire_Simple.png
Sequence Texture Effect production Use Sequence Texture to express animation in particles
Adjust Spawn Rate value to create natural flames