- every kind of fuel a pollution-constant (per MJ or per unit)
- every burner - instead of "emissions" an emission-factor
coal would have pollution 1.0 per MJ, solid fuel 0.8, wood 0.1 and something like "refined eco-fuel" 0.0
vanillas boiler would have emmission-factor 6.5, resulting in coal-feeded emission=pollution_constant*emmission-factor=1.0 * 6.5 = 6.5,
while an improved boiler could have factor 3.25, resulting in half emissions when burning coal.
BTW: It would be great to have a generic boiler/generator to create stuff like wind-turbines and solarthermic boilers without the need of performance-killing lua-scripts...