Introduction:
Detonation is a phenomenon that can occur in spark-ignition engines, where the air-fuel mixture ignites spontaneously and rapidly. This can cause excessive pressure and temperature rise, leading to engine damage. To prevent detonation, certain conditions need to be met in the charge away from the spark plug.

Explanation:
The given statements suggest three conditions that should be fulfilled in the charge away from the spark plug to prevent detonation. Let's analyze each statement individually.

1. Low temperature:
When the temperature of the charge away from the spark plug is low, it reduces the likelihood of spontaneous combustion or ignition. This is because a lower temperature implies a lower energy state of the molecules, making it more difficult for the mixture to ignite. Therefore, having a low temperature in the charge away from the spark plug can help prevent detonation.

2. Low density:
Low density of the charge away from the spark plug means that there is a lower concentration of air and fuel molecules in the mixture. This can have a similar effect to low temperature, as it reduces the likelihood of spontaneous ignition. With a lower density, the chances of the air-fuel mixture reaching the critical conditions required for detonation are reduced. Hence, low density can help prevent detonation in a spark-ignition engine.

3. Long ignition delay:
Ignition delay refers to the time between the spark plug firing and the start of combustion. A long ignition delay means that there is a delay in the initiation of combustion, which can be beneficial in preventing detonation. It allows the flame front to propagate more uniformly and stabilize before reaching the charge away from the spark plug. This helps to avoid sudden pressure rise and temperature spikes, which are characteristic of detonation.

Conclusion:
All three statements are correct in the context of preventing detonation in a spark-ignition engine. Low temperature and low density in the charge away from the spark plug reduce the likelihood of spontaneous ignition, while a long ignition delay allows for a more controlled combustion process. By fulfilling these conditions, the risk of detonation can be minimized, ensuring the reliable and safe operation of the engine.