common rail fuel systems), keeping fuel filters in good condition is more critical as debris can damage the pumps and injectors when waste vegetable oil or waste engine oil are used. Disadvantages Fuel efficiency with diesel engines is lower than with direct injection as the larger exposed areas tend to dissipate more heat and the air moving through the ports tending to increase pressure drops. However, using higher compression ratios will somewhat negate this inefficiency. Glow plugs are needed for a cold engine start on diesel engines; many indirect injection diesel engines cannot start at all in cold weather without glow plugs. Because the heat and pressure of combustion is applied to a very small area on the piston as it exits the precombustion chamber or swirl chamber, such engines are less suited to high specific power outputs (such as turbocharging, supercharging, or tuning) than direct injection diesels. The increased temperature and pressure on one part of the piston crown causes uneven expansion which can lead to cracking, distortion, or other damage, although advancements in manufacturing techniques have allowed manufacturers to largely mitigate the effects of uneven expansion, allowing for indirect injection diesels to use turbocharging. Indirect engines are often much noisier than direct injection common-rail engines. Starting fluid ("ether") often cannot be used in an indirect injection diesel engine as the glow plugs greatly increase the risk of preignition compared to direct injection diesels. See also Harry Ricardo Prosper L'Orange Premixed flame References Fuel injection systems