It's unlikely to affect the engine. Particles are typically <1 micron so won't be caught in the typical air filter and shouldn't be abrasive or corrosive passing through the engine.
It can get pretty smelly passing near wildfires. A bit like having a smoker in the cockpit.
In terms of visibility in smoke,
this guidance is offered:
Table 1: Estimating particulate matter concentrations from visibility assessment
Categories Visibility in Miles Particulate matter levels*
(1-hour average, µg/m3
)
Good 10 miles and up 0 - 40
Moderate 6 to 9 41 - 80
Unhealthy for Sensitive Groups 3 to 5 81 - 175
Unhealthy 1 1/2 to 2 1/2 176 - 300
Very Unhealthy 1 to 1 1/4 301 - 500
Hazardous 3/4 mile or less over 500