Try experimenting with flash and without, as demonstrated in these images. When using the flash, “bracket” your exposures – underexposing at a full stop (-1), 2/3rd stop (-.7), 1/3rd stop (-.3) – to see the variations in detail and lighting. By underexposing the flash you can avoid washing out details in the foreground which would cause the flames to look washed out as well. Most DSLR cameras allow independent flash exposure adjustments. Some brands allow settings to be made using controls on the camera body, while others allow the adjustments on the flash (speedlight) instead of the camera. Check your owner’s manual for complete details or ask an expert at your local photo special retailer.