I do believe that Chengdu is part of the visa transit program (applicable if you are traveling from one country to another with a layover in China, if you are going elsewhere in China it is not applicable).
However, I would consider whether you really have enough time. What time does your plane land? If early morning, great - if late at night, probably best to stay in the airport. Remember that the 17 hours is greatly reduced by the time it takes to deplane, you will have to gather your luggage and go through security and customs, obtain the transit visa... Then if you are going on to another country, you need to be at the gate at least an hour prior to takeoff so at the airport at least two hours prior to takeoff. You will have to go back through checkin, security and customs beforehand.
I would say that your 17 hours is now reduced to at least 11 or 12 hours... if during the day, is it worth it to carry your luggage with you for that many hours everywhere you go? What do you want to see (most things are distant from the airport, and China s traffic can be congested)?
I am not trying to talk you out of it, just want you to have realistic expectations. Also, have a plan in case you miss your flight out.