Quote:
Originally Posted by t vago
Yes, water injection will allow people to safely run with a leaner-than-normal charge mixture. Ordinarily, leaner mixtures tend to have slower burn rates, which would be handled in olden times by advancing the ignition timing. This would allow all of the usable heat energy to be turned into mechanical work. However, with today's cars, ignition timing cannot be adjusted. As a result, some of that otherwise available heat energy is left in the exhaust gas. This heats up the engine block more than normal, and if left unchecked, will create conditions that will cause engine destroying detonation and pre-ignition.
Water injection will serve to cool off the charge mixture to be burned in the engine. This will lower peak combustion temperature, and will move the engine away from detonation/pre-ignition conditions. For this reason, water injection is sometimes considered to be an anti-knock additive (another term for detonation is spark knock).
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The bolded part is incorrect. Ignition timing changes are the heart & soul of the aftermarket performance industry. Even when you have a commuter car that the performance industry hasn't cracked the ECU, There are interception/replacement options for ignition timing. Part of the reason to use water injection is to advance the timing to get to Minimum Best Timing, the start of the range of ignition timing for a given operating condition that produces the most torque/power. Most turbo engines cannot hit MBT without knock, even with premium gas when under full boost.
Regardless of the timing, a lot of heat is lost to the exhaust. The data I've seen on operating engines says at light loads 30% of the thermal energy is lost to the exhaust and coolant *each*. Under heavy load, A higher percentage goes out the exhaust, because the cooling system generally hits a limit.