Lean Burn Combustion

Topics: Internal combustion engine, Lean burn, Fuel injection Pages: 7 (2401 words) Published: March 13, 2011
Lean burn refers to the use of lean mixtures in an internal combustion engine. The air-fuel ratios can be as high as 65:1, so the mixture has considerably less fuel in comparison to the stoichiometric combustion ratio (14.7:1 for petrol for example). Contents[hide] * 1 Principle * 2 Chrysler Lean Burn computer * 3 Heavy-duty gas engines * 4 Honda lean burn systems * 4.1 Applications * 5 Toyota lean burn engines * 5.1 Applications * 6 Nissan lean burn engines * 6.1 Applications * 7 Mitsubishi Vertical Vortex (MVV) * 8 Diesel engines * 9 See also * 10 Footnotes * 10.1 Citations * 10.2 References| [edit] Principle

A lean burn mode is a way to reduce throttling losses. An engine in a typical vehicle is sized for providing the power desired for acceleration, but must operate well below that point in normal steady-speed operation. Ordinarily, the power is cut by partially closing a throttle. However, the extra work done in pumping air through the throttle reduces efficiency. If the fuel/air ratio is reduced, then lower power can be achieved with the throttle closer to fully open, and the efficiency during normal driving (below the maximum torque capability of the engine) can be higher. The engines designed for lean burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust hydrocarbon emissions than those found in conventional petrol engines. Ultra lean mixtures with very high air-fuel ratios can only be achieved by direct injection engines. The main drawback of lean burning is that a complex catalytic converter system is required to reduce NOx emissions. Lean burn engines do not work well with modern 3-way catalytic converter—which require a pollutant balance at the exhaust port so they can carry out oxidation and reduction reactions—so most modern engines run at or near the stoichiometric point. Alternatively, ultra-lean ratios can reduce NOx emissions[citation needed]. [edit] Chrysler Lean Burn computer

From 1976 through 1989, Chrysler equipped many vehicles with their Electronic Lean Burn (ELB) system, which consisted of a spark control computer and various sensors and transducers. The computer adjusted spark timing based on manifold vacuum, engine speed, engine temperature, throttle position over time, and incoming air temperature. Engines equipped with ELB used fixed-timing distributors without the traditional vacuum and centrifugal timing advance mechanisms. The ELB computer also directly drove the ignition coil, eliminating the need for a separate ignition module. ELB was produced in both open-loop and closed-loop variants; the open-loop systems produced exhaust clean enough for many vehicle variants so equipped to pass 1976 and 1977 US Federal emissions regulations, and Canadian emissions regulations through 1980, without a catalytic converter. The closed-loop version of ELB used an Oxygen sensor and a feedback carburetor, and was phased into production as emissions regulations grew more stringent starting in 1981, but open-loop ELB was used as late as 1990 in markets with lax emissions regulations, on vehicles such as the Mexican Chrysler Spirit. The spark control and engine parameter sensing and transduction strategies introduced with ELB remained in use through 1995 on Chrysler vehicles equipped with throttle-body fuel injection[citation needed]. Although Chrysler published extensive training and procedural manuals on ELB, it — like most early emission control systems — was complicated to troubleshoot without these manuals. Many Lean Burn computers have been replaced with a standalone electronic ignition module and centrifugal/vacuum advance distributor,[1] a retrofit to maintain fuel economy and driveability. [edit] Heavy-duty gas engines

Lean burn concepts are often used for the design of heavy-duty natural gas, biogas, and liquefied petroleum gas (LPG) fuelled engines. These engines can either be...
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