During a discussion on start-and-stop vehicle technology some bloke began pushin

Question

During a discussion on start-and-stop vehicle technology some bloke began pushing the point that re-starting the car uses stored energy from the battery, which needs to be replenished by increased fuel usage once the engine is moving. Well, this is obvious, the question is that of significance of such additional usage, especially in comparison with savings from reduced idle. Common sense tells me that this is splitting hairs: if ICE efficiency outlays put all accessory usage at 2 to 3% of overall energy consumption, which includes AC, and all electricals, then it can

Explanation / Answer

First, consider the case with negligible auxiliary loads (no air conditioning).

For a Civic-sized engine (1.8 liters), this US DOE worksheet estimates about 0.3 US gallon/hour fuel consumption at idle.

Here is a conservative starter calculation:

The Civic starter is rated at 1.0 kW (83A

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