Only diesel approved for installation in Cessnas are the Thielert Centurions of Diamond fame as far as I know. They're STC'd in C172s, PA28s (up to 160 hp versions) and ofcourse installed in Diamond Stars. Meridian is distributor of these engines I believe.
Seriously, I think the thielert is a good deal. Besides new engine you also get a new prop and other stuff - basically firewall forward replacement. The real upside is the rather ridiculous fuel burn. I flew a Diamond Star at 100 knots on roughly 4 US gallons/hr - Jet A !
Compared to the SMA engine (Renault design) the cost is only half. The hp is also less but they're asking more than $80000 for the SMA replacement, compared the $40000 of the Thielert !!!
Don't know if there will be diesel for 152s but it IS the future for GA so I don't see how it could be otherwise in a few years.