A compression ignition internal combustion engine system includes an engine and an exhaust system with an upstream exhaust conduit, a downstream exhaust conduit, and an exhaust placement mechanism for mixing exhaust with fuel and air within engine cylinders. The upstream exhaust conduit has a raw exhaust inlet, a raw exhaust outlet, and a diesel exhaust fluid (DEF) inlet between the raw exhaust inlet and the raw exhaust outlet. The downstream exhaust conduit includes a bare particulate filter and a selective catalytic reduction (SCR) device. Related methodology including operating the engine in a startup mode, and in a running mode once the SCR device is warmed, is also disclosed.