Chci rozpálit gril na vysoký žár.

In Czech, the subject pronoun is often omitted because the verb ending already shows who is doing the action.

• chci = I want
• The -i ending tells you it is I

So Chci rozpálit gril... is completely natural.
You could say Já chci... if you want emphasis, for example:

• Já chci rozpálit gril, ne ty. = I want to heat up the grill, not you.

Chci is the 1st person singular present tense of chtít (to want).

A few forms of chtít:

• chci = I want
• chceš = you want
• chce = he/she/it wants
• chceme = we want
• chcete = you plural / formal want
• chtějí = they want

So in this sentence, chci means I want.

This is about aspect, which is very important in Czech.

• rozpálit is perfective
• rozpalovat is imperfective

Here, rozpálit is used because the speaker wants to achieve a result: getting the grill hot. After chci, Czech often uses the infinitive that matches the intended meaning.

• chci rozpálit gril = I want to heat the grill up / get it hot
• chci rozpalovat gril would sound more like wanting to be in the process of heating it up, which is usually less natural here

So rozpálit fits the idea of a completed goal.

Rozpálit means something like:

• to heat up strongly
• to make very hot
• to fire up

With a grill, it suggests bringing it to a high heat, not just warming it a little.

It comes from pálit, which is connected with burning or strong heat, so rozpálit has a stronger feel than a neutral ohřát (to warm up).

Because gril is the direct object of rozpálit, it must be in the accusative case.

Here is the useful part:
gril is a masculine inanimate noun, and in the singular, the accusative is the same as the nominative.

So:

• nominative: gril
• accusative: gril

That is why the form does not change.

This phrase uses na + accusative to express the resulting level or state.

So:

• na vysoký žár = to a high heat

This is similar to other Czech patterns where na shows what something is brought to:

• ohřát vodu na 80 stupňů = heat the water to 80 degrees
• nastavit troubu na maximum = set the oven to maximum

In your sentence, the idea is: make the grill reach a high level of heat.

Because na here takes the accusative, not the locative.

So:

• na vysoký žár = accusative, showing a target/result

Not:

• na vysokém žáru = locative, which would mean something like on/at high heat, describing a location/state rather than a change toward it

As for vysokou teplotu, that is also possible in some contexts, but it is a different phrase:

• na vysokou teplotu = to a high temperature
• na vysoký žár = to high heat / intense heat

With grilling, žár sounds vivid and natural because it suggests strong radiant heat.

Žár is in the accusative singular because it follows na in a direction/result meaning.

žár is a masculine inanimate noun.

For masculine inanimate nouns in the singular, the accusative often looks like the nominative. The adjective agrees with the noun, so:

• nominative: vysoký žár
• accusative: vysoký žár

That is why you see vysoký, not vysokou or vysokém.

Yes. Czech word order is flexible, although the neutral version here is:

• Chci rozpálit gril na vysoký žár.

Other orders are possible, but they change emphasis:

• Gril chci rozpálit na vysoký žár.
  Emphasizes the grill
• Na vysoký žár chci rozpálit gril.
  Emphasizes the high heat
• Chci gril rozpálit na vysoký žár.
  Also possible, with slightly different flow

A learner should usually treat the original version as the safest neutral pattern.

Yes, chci is one of the forms learners often notice.

Roughly:

• ch in Czech is like the ch in Scottish loch or German Bach
• then ts
• then i

So chci is approximately kh-tsee, said quite quickly.

Native speakers naturally run the sounds together. Even if it feels awkward at first, this form is very common, so it becomes easier with practice.

Yes, gril is masculine inanimate.

Some singular forms:

• nominative: gril
• genitive: grilu
• dative: grilu
• accusative: gril
• locative: grilu
• instrumental: grilem

This matters because adjectives and sometimes verb-related patterns depend on the noun’s gender and case.

Possibly, but the nuance changes.

• rozpálit gril = get the grill really hot; fire it up strongly
• rozehřát gril = preheat the grill; heat it up
• ohřát gril = warm the grill up, often weaker or more general

So rozpálit is a strong and very suitable choice if you mean bringing the grill to serious cooking heat.