Lean-burn combustion

Natural gas engines can use lean-burn or stoichiometric combustion. Lean-burn combustion is similar to that which occurs in diesel engines, while stoichiometric combustion is more similar to the combustion in a gasoline engine. 

The NSR technology has been also applied to diesel engines, and is most reliable and attractive method for lean-burn combustion vehicles. Diesel particulate-NOx reduction system (DPNR) method is used to realize the simultaneous and continuous reduction of particulate and NOx is also recommended. This catalyst system is DPF combined with NSR catalyst. Soot on catalyst is removed during NOx reduction by occasional rich engine modification. Many other catalyst systems with NSR catalyst have been also developed. With decreasing S content in fuel and successive development of... 

Smith LL, Karim H, Castaldi MJ, Etemad S, PfefFerle WC Rich-catalytic lean-burn combustion for fuel-flexible operation with ultra-low emissions, Catal Today 117 438-446, 2006. 

The fact that Fischer-Tropsch fuels contain neither sulfur nor aromatics may become a strong selling point for the process. Less sulfur in the fuel has, of course, a direct effect on the sulfur oxides in the emissions, and the newly developed exhaust purification systems for lean burning engines that can be introduced means that all emissions, including GO2 and NOx, will diminish. Aromatics promote particulate formation in the combustion of diesel fuels and are therefore undesirable. We discuss this further in Ghapter 10. 

For similar motivations, there are limited incentives to develop an alternative SCR process for stationary sources based on methane (CH4-SCR) or other HCs, or based on NTP technologies, if not for specific, better applications. The situation is instead quite different for mobile sources, and in particular for diesel engine emissions. The catalytic removal of NO under lean conditions, e.g. when 02 during the combustion is in excess with respect to the stoichiometric one (diesel and lean-burn engines, natural gas or LPG-powered engines), is still a relevant target in catalysis research and an open problem to meet future exhaust emission regulations. 

Flammability limits Vapor-air mixtures will ignite and burn only over a well-specified range of compositions. The mixture will not burn when the composition is lower than the lower flammable limit (LFL) the mixture is too lean for combustion. The mixture is also not combustible when the composition is too rich that is, when it is above the upper flammable limit (UFL). A mixture is flammable only when the composition is between the LFL and the UFL. Commonly used units are volume percent fuel (percentage of fuel plus air). 

Lean burn/dry low-NOx combustors can generate NOx emissions levels as low as 9 ppm (at 15% 02), while those with liquid fuel combustors have NOx emissions limited to approximately 25 ppm (at 15% 02). There is no substantial difference in general performance with either fuel. However, the different heats of combustion result in slightly higher mass flows through the expansion turbine when liquid fuels are used, and thus a very small increase in power and efficiency performance is obtained. Also, the fuel pump work with liquid fuel is less than with the fuel gas booster compressor, thereby further increasing net performance with liquid fuels. 

The steady-state characteristics of practical significance for a lean-burning jet combustor intended to control pollutant emissions are its lean operating limits for eflBcient, stable combustion i.e., the minimum operating equivalence ratios that yield acceptable levels of CO and un-bumed HC emissions. Those operating points that also yield acceptable... 

ICE internal combustion engine LB lean burn LDV light-duty vehicle LDT light-duty truck LLDT light light-duty truck LNC lean NO catalyst... 

RQL Combustion Rich Burn—Quick Quench—Lean Burn... 

D. Bradley, J. Hynes, M. Lawes and C.G.W. Sheppard, Limitations to Turbulence-Enhanced Burning Rates in Lean Burn Engines, International Conference on Combustion in Engines, Inst. Mech. Eng. (1988) 17. 

However, diesel engines and some gasoline engines are operated under lean-burn conditions, where the oxygen is fed in excess, i.e., 10-20% more than is required to meet the stoichiometry for combustion of the fuel [132,489]. Gold catalysts have therefore been examined for their potential in low-temperature activity to combat cold-start emission problems and removal of NOj, from lean-burn engines [202]. 

Additionally around 70% of N2 1 H2 also appears typically in a proportion of 1/3 with respect to CO.2,6 bDifferences between the lean and stoichiometric condition in this engine affect mainly to the O2 concentration but also to the other components.5 7 cNO + NO2. dA large variety of hydrocarbons can be produced as a function of the type of fuel employed see Ref. 1 for details. emainly SO2, in a vol.% of around 1/20 of the wt% sulphur content in the fuel. fAir-to-fuel mass ratio employed in the fuel combustion. SA = (actual A/F)/(stoichiometric A/F). hOscillating between lean-burn (most of the time) and quasi-stoichiometric condition. 

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