The temperature of exhaust gases can vary widely depending on the source and context. Here are some general examples:

1. Automobile Exhaust:
   • At the tailpipe, exhaust gases can range from 300°C to 500°C (572°F to 932°F).
   • Inside the exhaust manifold, temperatures can be higher, from 500°C to 800°C (932°F to 1472°F).
2. Industrial Boilers:
   • Exhaust gases from industrial boilers can range from 150°C to 550°C (302°F to 1022°F), depending on the type of fuel used and the efficiency of the boiler.
3. Jet Engines:
   • The exhaust temperature of jet engines can reach up to 1,500°C (2732°F) or higher, especially in afterburning engines.
4. Power Plants:
   • Exhaust gases from power plants, such as those using natural gas or coal, typically range from 200°C to 600°C (392°F to 1112°F).

The exact temperature depends on many factors, including the type of engine or system, the fuel used, and the efficiency of combustion.

The amount of water in exhaust gases depends on the type of fuel burned and the combustion process. Here are some general estimates for different scenarios:

1. Automobile Exhaust:
   • Gasoline engines: For every gallon of gasoline burned, approximately 0.8 to 1.2 gallons of water is produced in the form of vapor.
   • Diesel engines: Similar to gasoline, diesel combustion produces water vapor, though the exact amount can vary slightly based on engine efficiency and fuel composition.
2. Natural Gas Combustion:
   • Natural gas (mainly methane, CH4) combustion produces a significant amount of water vapor. For every cubic meter of natural gas burned, about 1.6 kilograms of water is produced.
3. Industrial Boilers and Power Plants:
   • The water content in exhaust gases from industrial boilers or power plants will vary depending on the fuel used. For example, burning coal, oil, or natural gas will produce water vapor as a byproduct, with the amount dependent on the hydrogen content of the fuel.
4. Jet Engines:
   • Jet fuel (kerosene) combustion in jet engines produces water vapor. For every kilogram of jet fuel burned, about 1.26 kilograms of water is produced.

In general, water vapor is a significant component of exhaust gases from the combustion of hydrocarbon fuels. This water vapor can condense under certain conditions, forming visible steam or condensation, especially in cooler temperatures.

A safe exhaust temperature varies depending on the application and context. Here are some general guidelines for different scenarios:

1. Automobile Engines:
   • For gasoline engines, exhaust temperatures should generally not exceed 800°C (1472°F) at the exhaust manifold. Temperatures higher than this can indicate problems like lean fuel mixtures or issues with the catalytic converter.
   • Diesel engines typically have lower exhaust temperatures, around 300°C to 500°C (572°F to 932°F) at the exhaust manifold. Exceeding these temperatures might indicate turbocharger issues or excessive exhaust backpressure.
2. Industrial Boilers:
   • Safe exhaust temperatures for industrial boilers are usually between 150°C and 300°C (302°F to 572°F). Higher temperatures might indicate inefficiency or issues with heat recovery systems.
3. Power Plants:
   • Exhaust temperatures in power plants should be optimized for efficiency and emissions control. Typical exhaust temperatures range from 200°C to 400°C (392°F to 752°F). Excessively high temperatures can signal problems with combustion efficiency or heat recovery systems.
4. Jet Engines:
   • Safe exhaust temperatures for jet engines are much higher due to the nature of their operation. Temperatures can reach up to 1,500°C (2732°F) or more, especially with afterburners. Monitoring systems ensure these temperatures remain within safe operational limits to prevent engine damage.
5. Residential and Commercial Heating Systems:
   • For residential furnaces and water heaters, exhaust temperatures are usually in the range of 100°C to 200°C (212°F to 392°F). Proper venting and chimney systems are crucial to safely handle these temperatures and prevent overheating or fire hazards.

In all cases, maintaining exhaust temperatures within the recommended ranges helps ensure the safe and efficient operation of the system while preventing damage and reducing the risk of fire or other hazards. Regular maintenance and monitoring are essential to ensure temperatures remain within safe limits.