Whether you're a weekend DIY mechanic, a diehard gearhead, or just a vehicle owner curious about how your car works, you may want to know more about how the engine burns fuel to create power. Many common questions center on what causes engine overheating. You may be wondering just how hot it gets inside your car's engine, especially inside its hottest space — the combustion chamber. Well, wonder no more: we've done the research, and we have the answer for you!
The temperature of the burning gases inside the combustion chamber is typically around 2,800° F. In a diesel engine, this temperature remains fairly steady. In a gasoline-powered engine, the temperature can climb to 4,500° F or more under certain circumstances. However, the vehicle's engine cooling system keeps the walls of the combustion chamber at a temperature of between 265° F and 475° F.
In the remainder of this article, we'll describe how the combustion chamber gets so hot and what keeps the metal in the engine from melting down. We'll also explain why combustion chamber temperatures differ between diesel and gasoline engines. And we'll give you a few tips for making sure your car's engine stays cool even under harsh driving conditions. Keep reading to learn more!
How Hot Does A Combustion Chamber Get In A Vehicle?
The combustion chamber is the space within each cylinder of a car's engine where the fuel mixes with air, ignites, and burns. This process converts the chemical energy of the fuel into mechanical energy, which pushes a piston in the cylinder. The movement of the piston, in turn, starts a complex series of mechanical interactions that ultimately power the car.
However, the combustion process is inefficient: 70% of the energy from the burning mixture of fuel and air is released as heat. This drastically raises the temperature in the combustion chamber, and much of that heat is transferred to the walls of the combustion chamber and throughout the engine block.
The typical temperature of the burning gases inside an automotive combustion chamber is about 2,800° F. Of course, the metal parts of the engine cannot be allowed to get this hot: steel melts at 2500° F, and aluminum alloys melt at about 1200° F. When one or more of the metal parts in the engine reaches a critical temperature and begins to deform, catastrophic engine failure follows.
Therefore, modern automotive engines have intricate cooling systems designed to keep the metal surfaces in and around the combustion chamber at much lower temperatures. The following examples detail the typical temperatures of various combustion-related engine parts during normal operation:
- Intake valve: 475° F
- Exhaust valve: 1,200° F
- Spark plug: 1,100° F
- Piston face: 575° F
- Cylinder wall: 375° F
Similarly, a study by the Society of Automotive Engineers (SAE) found that the temperature of the combustion chamber walls (the top section of the cylinder wall), specifically, ranges from 265° F under limited throttle to 475° F with the throttle wide open.
How Hot Is Combustion?
The initial combustion temperature in a vehicle's engine is determined by two factors: the flame heat and the additional heat caused by the compression of the gases in the combustion chamber. Gasoline and diesel engines are different from each other in this regard, so we'll address them separately.
In a gasoline engine, after fuel is sprayed by the fuel injector into the combustion chamber, a spark plug ignites the fuel. The temperature of the resulting flame is about 2,600° F. Most gasoline engines have a compression ratio of 9:1 in the combustion chamber; this pressure adds about 200° F, raising the typical combustion temperature to 2,800° F.
Depending on the shape of the combustion chamber, the load on the engine, and the RPMs at which the car is being driven, the temperature of the burning gases in a gasoline engine can reach 4,500° F. In extreme situations, it can reach as much as 6,000° F.
By contrast, in diesel engines, the initial compression ratio is 20:1, heating the air to 1,200° F or more before fuel is sprayed into the combustion chamber. When the fuel ignites, the resulting combustion adds another 2,600° F, for a total initial combustion temperature of 3,800°F.
Immediately after the engine starts, the piston drops lower in the cylinder. This effectively increases the volume of the combustion chamber and decreases the compression ratio so that the temperature in the chamber drops. It stabilizes at about 2800° F. Unlike the gasoline engine, the diesel engine maintains this combustion temperature: whenever the thermostat senses the temperature rising, it signals the piston to drop lower in the cylinder.
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How Do You Cool A Combustion Chamber?
Given all the heat generated within the combustion chamber, it's critical that every engine has a well-designed cooling system. If the metal parts of the engine get too hot, they can melt, causing catastrophic engine failure. Car manufacturers have developed two major ways to cool the combustion chamber and the engine block.
Nearly all cars currently in production use a liquid cooling system to extract heat from the engine block. A pump sends coolant (water/ethanol mix) through a series of hoses and ports. As the coolant passes through the engine block, it extracts heat from the metal surfaces. The coolant then flows through the radiator, where it transfers heat to the thin metal fins, which then radiate that heat into the surrounding air.
As a vehicle owner, it's critically important that you keep your car's coolant at the optimal level, as described in your owner's manual. Most mechanics also recommend flushing the system and changing the coolant every two years or 30,000 miles.
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Ceramic Coating On Cylinder Head
Some manufacturers also put a ceramic coating on the inside of the cylinder head. Because ceramic does not readily transfer heat, this helps to protect the metal walls of the cylinder from absorbing and transferring heat to the rest of the engine block.
Things You Can Do To Keep Your Engine Block Cooler
If you own a relatively new car, there is little you need to do to protect your engine from the heat of combustion other than to make sure you keep the coolant fresh and topped off. But if you have an older car — especially a vintage muscle car that you like to drive hard — here are a few tips for keeping your engine cool.
Install A Better Radiator
Replace your old copper-and-brass radiator with a quality, high-efficiency radiator made of aluminum alloy. It's up to 30 pounds lighter, and it will dissipate heat much faster, keeping your engine cool without compromising performance.
A word of caution: make sure you purchase a radiator that's specifically designed for your car's make, model, and year, so all the screw holes and valve/hose openings will be in the right places.
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Put In A Stronger Coolant Pump
Replace your old, heavy coolant pump with a new, lighter, and more efficient one. The more effectively your pump gets coolant through the engine and to the radiator, the better it will cool your engine block.
Edelbrock makes a wide range of coolant pumps for vintage cars and trucks, and the quality is excellent. Again, be sure to exactly match the make, model, and year of your vehicle.
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Create More Airflow With An Upgraded Fan
Switching out your car's old radiator fan for an updated one can get more air flowing across the radiator. And more airflow means better, quicker cooling. Mechanical fans are generally best, but a high-quality electric fan can do an excellent job, as well. The size and shape of the fan you select may depend on what other modifications you've made to your engine and what space is available for the fan.
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Is The Combustion Chamber Part Of The Cylinder Head?
The combustion chamber is part of the cylinder head. Specifically, it is the space within the cylinder that is bounded by the crown of the piston (bottom), the inside-top of the cylinder (top), and the walls of the cylinder (sides). The volume of the combustion chamber changes depending on the position of the piston.
Here's how it works. Most vehicle engines contain 4, 6, or 8 cylinders. Each cylinder has a piston inside it, which slides up and down in a four-stroke cycle:
- Intake: the piston head is at its lowest point in the cylinder. The volume of the combustion chamber is at its maximum. Fuel sprays into the chamber through the intake valve at the top of the cylinder head.
- Compression: the piston head rises, compressing the air/fuel mixture. The volume of the combustion chamber shrinks. The compression raises the temperature of the air/fuel mixture.
- Combustion: the piston head is at its highest point in the cylinder. The volume of the combustion chamber is at its minimum. The fuel/air mixture ignites and burns, releasing heat and mechanical energy.
- Exhaust: the piston descends to its lowest point in the cylinder. The volume of the combustion chamber increases to maximum. The mechanical energy from combustion moves the piston; the heat is released through the exhaust valve at the top of the cylinder.
How Hot Is An Engine Cylinder?
During normal operation, the walls of an engine cylinder can heat up to 375° F. Of course, without a high-functioning cooling system, the cylinder would get much hotter and would eventually melt. It's particularly important to keep the temperature of the cylinder walls at 375° F or lower because higher temperatures would harden any carbon deposits on the walls, resulting in carbon buildup and negatively impacting performance.
The temperature inside the engine of your car, especially within the combustion chamber, is hot, hot, hot! Now that you know just how hot things can get under the hood, you'll better understand how important it is to keep your car's engine cooling system working at maximum efficiency. Knowing that all that heat is being channeled away from the engine and out through the radiator, you can keep cruising down the highway, confident that your ride will abide!
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