Fuel Filter Mahle Original - KX 36 D D is one type of engine filter used to filter fuel before entering the engine. All combustion engines require clean air for optimal performance: modern diesel engines require about 15,000 liters of air - for every liter of fuel burned! Deutz air filters provide reliable combustion air filtration, prevent dust from entering the engine and cause increased wear and fuel consumption, higher performance loss and emissions. Perfect protection for your machine.