Lean Burn Engines

摘要

Natural gas internal combustion engines are currently worthy of attention due to the growing interest in energy generation equipments that are both efficient and environmentally friendly. As an answer to this interest, natural gas engine utilizing lean burn combustion technology have been introduced instead of traditional stoichiometric engines with two positive effects. First, excess air in the mixture reduces combustion process temperature, which reduces the formation of NO_x with respect to conventional stoichiometric engines. Second, due to excess Oxygen, the combustion process is more efficient and more energy is generated from the same amount of fuel. Another relevant characteristic of mixture leaning is keeping the engine away from the knocking zone. Since, the ideal working of a lean burn engine occurs within a narrow window, it requires a more accurate fuel flow, ignition time, air-fuel ratio controls as well as a higher level of external variable monitoring to avoid engine knocking, combustion fault (misfire) and resulting damage to the equipment. Due to the aforementioned requirements, those engines are equipped with electronic controls of the type "Full Authority", which are essential to assure the combustion will occur within those limits. The objective of this study is to discuss, with empirical data, mixture leaning of lean burn technology engines and Full Authority controls types as well as the effects of greenhouse gas emissions, exhaust gas temperatures and keeping the engine away from knocking zone.