science

Petrol engine

Petrol engine is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Petrol engine rather than just read about it. In short: A petrol engine is an internal combustion engine that runs on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as E10 and E85).

Key takeaways

Petrol engine belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Petrol engine to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Petrol engine from memory before moving on to harder problems.

Reference excerpt

A petrol engine is an internal combustion engine that runs on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as E10 and E85). They may be designed to run on petrol with a higher octane rating, as sold at petrol stations. Most petrol engines use spark ignition, unlike diesel engines which run on diesel fuel and typically use compression ignition. Another key difference to diesel engines is that petrol engines typically have a lower compression ratio.

History

The first practical petrol engine was built in 1876 in Germany by Nicolaus August Otto and Eugen Langen, although there had been earlier attempts by Étienne Lenoir in 1860, Siegfried Marcus in 1864 and George Brayton in 1873.

Design

Thermodynamic cycle

Most petrol engines use either the four-stroke Otto cycle or the two-stroke cycle. Petrol engines have also been produced using the Miller cycle and Atkinson cycle.

Layout Most petrol-powered piston engines are straight engines or V engines. However, flat engines, W engines and other layouts are sometimes used. Wankel engines are classified by the number of rotors used.

Compression ratio

Cooling

Petrol engines are either air-cooled or water-cooled.

Ignition

Petrol engines use spark ignition. High voltage for the spark this may be provided by a magneto or an ignition coil. In modern car engines, the ignition timing is managed by an electronic Engine Control Unit. Ignition modules can also function as a rev limiter in some cases to prevent overrevving and the consequences of it, such as valve float and connecting rod failure.

Primer Primers may be used to help start the engine. They can draw fuel from fuel tanks and vaporize fuel directly into piston cylinders. Engines are difficult to start during cold weather, and the fuel primer helps because otherwise there will not be enough heat available to vaporize the fuel in the carburetor.

Power output and efficiency

The power output of small- and medium-sized petrol engines (along with equivalent engines using other fuels) is usually measured in kilowatts or horsepower. Typically, petrol engines have a thermodynamic efficiency of about 20-30% (approximately half that of some diesel engines).

Applications Applications of petrol engines include automobiles, motorcycles, aircraft, motorboats and small engines (such as lawn mowers, chainsaws and portable generators). Petrol engines have also been used as "pony engines", a type of engine used to start a larger, stationary diesel engine.

See also Diesel engine Electric motor Hydrogen engine Jet engine

Notes

References

Illustrations

Petrol engine: Animation of an Otto cycle engine — Animation of an Otto cycle engine

Worked examples

Example 1 — a first encounter with Petrol engine

Start with the simplest possible case. Write down what Petrol engine claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Petrol engine before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Petrol engine ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Petrol engine

In research: Petrol engine appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Petrol engine in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Petrol engine is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1876 introductions, Gasoline engines, German inventions, so understanding it makes those chapters shorter.
In everyday life: Look for Petrol engine outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Petrol engine in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Petrol engine means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Petrol engine out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Petrol engine in simple terms?

Why does Petrol engine matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Petrol engine?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Petrol engine.