Set default value in select when the ng-model is null

I'm new to angular and i'm trying to set a default state to select when my ng-model is null. Basically I want to set it to 'None' if the model is empty. I tried the below code but it's not working.

<select ng-init="item.carType | item.carType='none'" ng-model="item.carType">
    <option value="none">None</option>
    <option value="manual">Manual</option>
    <option value="auto">Auto</option>                      
</select>