This improves the combustion of biodiesel and reduces the particulate emissions from unburnt carbon. An excessively rich fuel to air ratio will increase unburnt hydrocarbon pollutants from the engine. A poor injector performance causes unburnt propellant to leave the engine, giving poor efficiency. Her charred skeleton is brought out, clutching an unburnt severed hand. The 2003 fires created a mosaic of burnt and unburnt areas. For example, the loss on ignition of fly ash consists of contaminant unburnt fuel. Fuel reduction, indirect firelines, contingency firelines, backburning and wetting unburnt fuels are examples. Unburnt castor oil from the engine had a laxative effect on the pilot if ingested. Near the vicarage, a few unburnt graves from the Viking Age have been excavated. Plants can also colonise unburnt sites with ample sunlight. Fragments of unburnt human bone have also been found in the ditch-fill. In Attica, the normal unburnt clay was of orange colour at this stage. Venting of unburnt gas is only permitted for safety reasons or in an emergency. On this plate was deposited a piece of unburnt bone of uncertain derivation. He noted that the pine in the unburnt area was excellent.