bèiyòng ránliào zài zhèlǐ.

The pattern is:

subject + 在 + location

So here:

• 备用燃料 = the subject
• 在 = indicates location
• 这里 = the location

A very literal breakdown is:

• 备用燃料 = reserve / backup fuel
• 在这里 = is here

This is a very common Chinese way to say where something is.

Because this sentence is about location, not identification.

In Chinese, when you say where something is, you usually use 在 rather than 是.

• X 在 Y = X is at/in Y
• X 是 Y = X is Y

So:

• 备用燃料在这里。 = The backup fuel is here.
• 备用燃料是这里。 would be wrong, because it would mean something like The backup fuel is here-place, which does not make sense.

This is a very important beginner pattern:

• 书在桌子上。 = The book is on the table.
• 他在家。 = He is at home.

Here, 备用 is modifying 燃料.

So 备用燃料 means:

• reserve fuel
• backup fuel
• spare fuel

In this sentence, 备用 works like an attributive modifier before the noun 燃料.

By itself, 备用 can also function more verbally in other contexts, with the idea of keeping something in reserve or for backup use. But in 备用燃料, it is best understood as a modifier: backup/reserve fuel.

Because in Chinese, short, close modifiers often go directly before the noun without 的.

So:

• 备用燃料 = backup fuel

This is very normal and natural.

Using 的 is sometimes possible in other contexts, but here it would usually sound less compact and less like a fixed noun phrase. Compare:

• 备用燃料 = the normal, concise form
• 备用的燃料 = possible, but more explicitly fuel that is kept as backup

So in this sentence, 备用燃料 is the most natural form.

In beginner-level grammar, it is usually easiest to treat 在 here as the main verb meaning to be located at.

So in:

• 备用燃料在这里。

在 is the predicate of the sentence: it tells you where the fuel is.

In other sentences, 在 can also behave more like a preposition/coverb, especially before another verb, for example:

• 他在学校学习。 = He studies at school.

But in your sentence, the simplest understanding is:

• 在 = is located at / is in

Not usually as the main reading.

备用燃料在这里 most naturally means:

• The backup fuel is here.

That is, you are talking about a specific thing and saying where it is.

If you want to say There is backup fuel here, Chinese more naturally uses 有:

• 这里有备用燃料。 = There is backup fuel here.

So the difference is:

• 备用燃料在这里。 = The backup fuel is here.
• 这里有备用燃料。 = There is backup fuel here.

This is a very useful contrast:

• 在 = tells location of something already being talked about
• 有 = says that something exists somewhere

They both mean here.

• 这里 is a bit more standard and is common in both speech and writing.
• 这儿 is very common in spoken Mandarin, especially in northern speech.

So these are both fine:

• 备用燃料在这里。
• 备用燃料在这儿。

The meaning is the same. The difference is mostly style and regional speech preference.

In careful citation form, 这里 is often written as zhèlǐ, with 里 as third tone.

But in natural speech, the second syllable is very often weakened, so it sounds more like:

• zhèli

So learners will hear both kinds of descriptions:

• dictionary-style: zhèlǐ
• common spoken pronunciation: zhèli

Both are useful to know. If you say zhèlǐ clearly, people will understand you perfectly. As your speech becomes more natural, you will often hear and use zhèli.

The other words are pronounced:

• 备用 bèiyòng
• 燃料 ránliào
• 在 zài
• 这里 zhèlǐ / zhèli

Yes, that is possible, but it is slightly different in feel.

• 备用燃料在这里。 = more compact and natural as a noun phrase: backup fuel
• 备用的燃料在这里。 = more explicitly the fuel that is for backup use

So the version without 的 sounds tighter and more natural in many ordinary contexts.

A similar English comparison would be:

• backup fuel
• fuel that is kept as backup

Both work, but one is shorter and more idiomatic as a label.

Not if you want to mean backup fuel.

To modify a noun in Chinese, the modifier normally goes before the noun:

• 备用燃料 = backup fuel

If you say 燃料备用, it no longer works as a normal noun phrase meaning backup fuel. It would sound incomplete or like part of a different structure.

So for this meaning, keep the order:

• 备用 + 燃料

This is a very common Chinese pattern:

• 汽油 = gasoline
• 备用汽油 = backup gasoline
• 文件 = documents
• 备用文件 = backup documents

Yes. It is a perfectly complete Chinese sentence.

Chinese often allows very short sentences when the context is clear. Here, the sentence gives all the necessary information:

• what: 备用燃料
• where: 在这里

So 备用燃料在这里。 is fully grammatical and natural.

Chinese often sounds more concise than English in this way. You do not need extra words like the, is, or located if the structure already makes the meaning clear.