CHT and EGT are two important parameters that are monitored in internal combustion engines to ensure their efficient operation and prevent potential damage. Understanding the relationship between CHT and EGT and why CHT typically peaks before EGT can provide valuable insights into the engine's performance and health.
1. Heat Transfer and Combustion Process:
During the combustion process in an engine, a significant amount of heat is generated due to the burning of fuel. This heat is initially absorbed by the cylinder head, which is in close proximity to the combustion chamber. The cylinder head acts as a heat sink, absorbing the heat generated during the combustion process. As a result, the CHT starts to rise rapidly as heat accumulates in the cylinder head.
2. Exhaust Gas Cooling Effect:
As the hot gases produced by combustion move through the exhaust system, they start to cool down. This cooling process is facilitated by the exhaust manifold and the exhaust pipe, which dissipate heat into the surrounding environment. As the gases cool, their temperature, known as EGT, decreases.
3. Time Lag:
There is a time lag between the occurrence of peak CHT and peak EGT. This is because the heat absorbed by the cylinder head has to be transferred to the exhaust gases before it can be measured as EGT. The heat transfer process takes some time, resulting in a delay between the CHT peak and the EGT peak.
Relationship between CHT and EGT that would indicate an engine problem:
1. CHT and EGT Correlation:
In general, there is a positive correlation between CHT and EGT. As CHT increases, EGT also tends to increase, as more heat is transferred from the cylinder head to the exhaust gases. However, if the EGT is consistently lower than expected for a given CHT, it could indicate potential issues such as a restricted exhaust system or a faulty exhaust gas temperature sensor.
2. CHT Spikes and EGT:
Sudden spikes in CHT without a corresponding increase in EGT may suggest problems related to cooling system efficiency. This could be due to issues with the coolant flow, a malfunctioning thermostat, or air pockets in the cooling system.
3. EGT Spikes and CHT:
Abrupt spikes in EGT while CHT remains relatively stable could indicate issues such as a lean air-fuel mixture, excessive fuel injection, or problems with the ignition timing. These conditions can cause higher combustion temperatures and increased exhaust gas temperatures.
4. CHT and EGT Trends:
Long-term trends in CHT and EGT data can also provide valuable information. If CHT and EGT levels consistently exceed recommended values, it could point towards engine issues such as worn piston rings, valve problems, or injector issues.
By monitoring the relationship between CHT and EGT and understanding their trends, deviations, and correlations, it is possible to identify potential engine problems at an early stage, allowing for timely maintenance and repairs.
