Lean burn
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Lean-burn refers to the burning of fuel with an excess of air in an
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
. In lean-burn engines the air:fuel ratio may be as lean as 65:1 (by mass). The air / fuel ratio needed to stoichiometrically combust gasoline, by contrast, is 14.64:1. The excess of air in a lean-burn engine emits far less hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.


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
engine An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power ...
s designed for lean-burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low
exhaust Exhaust, exhaustive, or exhaustion may refer to: Law *Exhaustion of intellectual property rights, limits to intellectual property rights in patent and copyright law **Exhaustion doctrine, in patent law ** Exhaustion doctrine under U.S. law, in p ...
hydrocarbon emissions than those found in conventional
gasoline engine A petrol engine (gasoline engine in American English) is an internal combustion engine designed to run on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as ''E ...
s. 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 A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...
system is required to reduce
NOx In atmospheric chemistry, is shorthand for nitric oxide () and nitrogen dioxide (), the nitrogen oxides that are most relevant for air pollution. These gases contribute to the formation of smog and acid rain, as well as affecting tropo ...
emissions. Lean-burn engines do not work well with modern 3-way
catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...
—which require a pollutant balance at the exhaust port so they can carry out oxidation and reduction reactions—so most modern engines tend to cruise and coastdown at or near the stoichiometric point.


Chrysler Electronic Lean-Burn

From 1976 through 1989,
Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automoti ...
equipped many vehicles with their Electronic Lean-Burn (ELB) system, which consisted of a spark control computer and various sensors and
transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and cont ...
s. 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 Emission standards are the legal requirements governing air pollutants released into the atmosphere. Emission standards set quantitative limits on the permissible amount of specific air pollutants that may be released from specific sources ove ...
, and Canadian emissions regulations through 1980, without a
catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...
. 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 Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All comp ...
.


Heavy-duty gas engines

Lean-burn concepts are often used for the design of heavy-duty
natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...
,
biogas Biogas is a mixture of gases, primarily consisting of methane, carbon dioxide and hydrogen sulphide, produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste and food waste. It is a ...
, and liquefied petroleum gas (LPG) fuelled engines. These engines can either be full-time lean-burn, where the engine runs with a weak air–fuel mixture regardless of load and engine speed, or part-time lean-burn (also known as "lean mix" or "mixed lean"), where the engine runs lean only during low load and at high engine speeds, reverting to a stoichiometric air–fuel mixture in other cases. Heavy-duty lean-burn gas engines admit twice as much tp://doc.nit.ac.ir/cee/m.jafari/motor/ICE%20projects-89/0%20(3).pdf aConseil Internationaldes Machines A Combustion – Paper.: 167 New Gas Engines – CIMAC Congress 2007, Vienna air as theoretically needed for complete combustion into the combustion chambers. The extremely weak air–fuel mixtures lead to lower combustion temperatures and therefore lower NOx formation. While lean-burn gas engines offer higher theoretical thermal efficiencies, transient response and performance may be compromised in certain situations. However, advances in fuel control and closed loop technology by companies lik
North American Repower
have led to production of modern CARB certified lean burn heavy duty engines for use in commercial vehicle fleets.http://arb.ca.gov/msprog/aftermkt/devices/eo/bseries/b-67-1.pdf Lean-burn gas engines are almost always turbocharged, resulting in high power and torque figures not achievable with stoichiometric engines due to high combustion temperatures. Heavy duty gas engines may employ precombustion chambers in the cylinder head. A lean gas and air mixture is first highly compressed in the main chamber by the piston. A much richer, though much lesser volume gas/air mixture is introduced to the precombustion chamber and ignited by spark plug. The flame front spreads to the lean gas air mixture in the cylinder. This two stage lean-burn combustion produces low NOx and no particulate emissions. Thermal efficiency is better as higher compression ratios are achieved. Manufacturers of heavy-duty lean-burn gas engines include MTU,
Cummins Cummins Inc. is an American multinational corporation that designs, manufactures, and distributes engines, filtration, and power generation products. Cummins also services engines and related equipment, including fuel systems, controls, air ...
,
Caterpillar Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Sym ...
, MWM,
GE Jenbacher INNIO Jenbacher designs and manufactures gas engines and cogeneration modules in the Austrian town of Jenbach in Tyrol. It is part of the INNIO portfolio of products and is one of their gas engine technologies; the other being Waukesha Engines. ...
,
MAN Diesel & Turbo MAN Energy Solutions SE is a German multinational company based in Augsburg that produces large-bore gas and diesel engines and also turbomachinery for marine, rail and stationary applications, as locomotive and marine propulsion systems, power ...
,
Wärtsilä Wärtsilä Oyj Abp (), trading internationally as Wärtsilä Corporation, is a Finnish company which manufactures and services power sources and other equipment in the marine and energy markets. The core products of Wärtsilä include technolo ...
,
Mitsubishi Heavy Industries is a Japanese multinational engineering, electrical equipment and electronics corporation headquartered in Tokyo, Japan. MHI is one of the core companies of the Mitsubishi Group and its automobile division is the predecessor of Mitsubishi Mo ...
, Dresser-Rand Guascor,
Waukesha Engine Waukesha is a brand of large stationary reciprocating engines produced by INNIO Waukesha Gas Engines, a business unit of the INNIO Group. For 62 years, Waukesha was an independent supplier of gasoline engines, diesel engines, multifuel engines ...
and
Rolls-Royce Holdings Rolls-Royce Holdings plc is a British multinational aerospace and defence company incorporated in February 2011. The company owns Rolls-Royce, a business established in 1904 which today designs, manufactures and distributes power systems for ...
.


Honda lean-burn systems

One of the newest lean-burn technologies available in automobiles currently in production uses very precise control of fuel injection, a strong air–fuel swirl created in the combustion chamber, a new linear air–fuel sensor (LAF type O2 sensor) and a lean-burn NOx catalyst to further reduce the resulting NOx emissions that increase under "lean-burn" conditions and meet NOx emissions requirements. This stratified-charge approach to lean-burn combustion means that the air–fuel ratio is not equal throughout the cylinder. Instead, precise control over
fuel injection Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines. All comp ...
and intake flow dynamics allows a greater concentration of fuel closer to the spark plug tip (richer), which is required for successful ignition and flame spread for complete combustion. The remainder of the cylinders' intake charge is progressively leaner with an overall average air:fuel ratio falling into the lean-burn category of up to 22:1. The older
Honda is a Japanese public multinational conglomerate manufacturer of automobiles, motorcycles, and power equipment, headquartered in Minato, Tokyo, Japan. Honda has been the world's largest motorcycle manufacturer since 1959, reaching a producti ...
engines that used lean-burn (not all did) accomplished this by having a parallel fuel and intake system that fed a pre-chamber the "ideal" ratio for initial combustion. This burning mixture was then opened to the main chamber where a much larger and leaner mix then ignited to provide sufficient power. During the time this design was in production this system ( CVCC, Compound Vortex Controlled Combustion) primarily allowed lower emissions without the need for a
catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...
. These were
carbureted A carburetor (also spelled carburettor) is a device used by an internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the venturi tube in the main meteri ...
engines and the relative "imprecise" nature of such limited the MPG abilities of the concept that now under MPI (Multi-Port fuel Injection) allows for higher MPG too. The newer
Honda is a Japanese public multinational conglomerate manufacturer of automobiles, motorcycles, and power equipment, headquartered in Minato, Tokyo, Japan. Honda has been the world's largest motorcycle manufacturer since 1959, reaching a producti ...
stratified charge (lean-burn engines) operate on air–fuel ratios as high as 22:1. The amount of fuel drawn into the engine is much lower than a typical gasoline engine, which operates at 14.7:1—the chemical stoichiometric ideal for complete combustion when averaging gasoline to the petrochemical industries' accepted standard of C8H18. This lean-burn ability by the necessity of the limits of physics, and the chemistry of combustion as it applies to a current gasoline engine must be limited to light load and lower RPM conditions. A "top" speed cut-off point is required since leaner gasoline fuel mixtures burn slower and for power to be produced combustion must be "complete" by the time the exhaust valve opens.


Applications

*1992–95 Civic VX *1996–2005 Civic Hx *2002–05
Civic Hybrid The is a series of automobiles manufactured by Honda since 1972. Since 2000, the Civic has been categorized as a compact car, while previously it occupied the subcompact class. , the Civic is positioned between the Honda Fit/City and Honda Acc ...
*2000–06
Insight Insight is the understanding of a specific cause and effect within a particular context. The term insight can have several related meanings: *a piece of information *the act or result of understanding the inner nature of things or of seeing intu ...
Manual transmission & Japanese spec Cvt only


Toyota lean-burn engines

In 1984, Toyota released the 4A-ELU engine. This was the first engine in the world to use a lean-burn combustion control system with a lean mixture sensor, Toyota called "TTC-L" ( Toyota Total Clean-Lean-Burn). It was used in Japan on Toyota Carina T150 replacing the TTC-V (Vortex)
exhaust gas recirculation In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide () emissions reduction technique used in petrol/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust ...
approach used earlier, Toyota Corolla E80, and
Toyota Sprinter The is a compact car manufactured by Toyota as a variant of the Toyota Corolla. Exclusively sold in the Japanese domestic market, the Sprinter was aimed to be sportier than its Corolla sibling, with the Sprinter being sold at the '' Toyota Auto ...
. The lean mixture sensor was provided in the exhaust system to detect air–fuel ratios leaner than the theoretical air–fuel ratio. The fuel injection volume was then accurately controlled by a computer using this detection signal to achieve lean air–fuel ratio feedback. For optimal combustion, the following items were applied: program independent injection that accurately changed the injection volume and timing for individual cylinders, platinum plugs for improving ignition performance with lean mixtures, and high performance igniters."Toyota 4A-ELU engine"
"240 Landmarks of Japanese Automotive Technology" website
The lean-burn versions of the 1587cc 4A-FE and 1762cc 7A-FE 4-cylinder engines have 2 inlet and 2 exhaust valves per cylinder. Toyota uses a set of butterflies to restrict flow in every second inlet runner during lean-burn operation. This creates a large amount of swirl in the combustion chamber. Injectors are mounted in the head, rather than conventionally in the intake manifold. Compression ratio 9.5:1."Toyota Carina Specifications"
, auto.vl.ru japanese car specification website
The 1998cc 3S-FSE engine is a direct injection petrol lean-burn engine. Compression ratio 10:1."Toyota Corona Premio G"
, auto.vl.ru japanese car specification website


Applications


Nissan lean-burn engines

Nissan QG engines are a lean-burn aluminum
DOHC An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion c ...
4-valve design with
variable valve timing In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with var ...
and optional ''NEO Di'' direct injection. The 1497cc QG15DE has a Compression ratio of 9.9:1"Nissan Sunny"
, auto.vl.ru japanese car specification website
and 1769cc QG18DE 9.5:1."Nissan Avenir"
, auto.vl.ru japanese car specification website


Applications


Mitsubishi Vertical Vortex (MVV)

In 1991, Mitsubishi developed and began producing the ''MVV (Mitsubishi Vertical Vortex)'' lean-burn system first used in Mitsubishi's 1.5 L 4G15
straight-4 A straight-four engine (also called an inline-four) is a four-cylinder piston engine where cylinders are arranged in a line along a common crankshaft. The vast majority of automotive four-cylinder engines use a straight-four layout (with the ...
single-overhead-cam 1,468-cc engine. The vertical vortex engine has an idle speed of 600 rpm and a compression ratio of 9.4:1 compared with respective figures of 700 rpm and 9.2:1 for the conventional version. The lean-burn MVV engine can achieve complete combustion with an air–fuel ratio as high as 25:1, this boasts a 10–20% gain in fuel economy (on the Japanese 10-mode urban cycle) in bench tests compared with its conventional MPI powerplant of the same displacement, which means lower CO2 emissions."Engine Technology"
, Mitsubishi Motors South Africa website
"Honda can't sell lean-burn in California"
Joel D. Pietrangelo & Robert Brooks, ''
Ward's Auto World Ward's is an American organization that has covered the automotive industry for over 80 years. The organization is responsible for several publications including, ''Ward's AutoWorld'', and ''Ward's Dealer Business''. Ward's also publish the an ...
'', September 1991
The heart of the Mitsubishi's MVV system is the linear air–fuel ratio exhaust gas oxygen sensor. Compared with standard oxygen sensors, which essentially are on-off switches set to a single air/fuel ratio, the lean oxygen sensor is more of a measurement device covering the air/fuel ratio range from about 15:1 to 26:1. To speed up the otherwise slow combustion of lean mixtures, the MVV engine uses two intake valves and one exhaust valve per cylinder. The separate specially shaped (twin intake port design) intake ports are the same size, but only one port receives fuel from an injector. This creates two vertical vortices of identical size, strength and rotational speed within the combustion chamber during the intake stroke: one vortex of air, the other of an air/fuel mixture. The two vortices also remain independent layers throughout most of the compression stroke. Near the end of the compression stroke, the layers collapse into uniform minute turbulences, which effectively promote lean-burn characteristics. More importantly, ignition occurs in the initial stages of breakdown of the separate layers while substantial amounts of each layer still exist. Because the spark plug is located closer to the vortex consisting of air/fuel mixture, ignition arises in an area of the pentroof-design combustion chamber where fuel density is higher. The flame then spreads through the combustion chamber via the small turbulences. This provides stable combustion even at normal ignition-energy levels, thereby realizing lean-burn. The engine computer stores optimum air fuel ratios for all engine-operating conditions—from lean (for normal operation) to richest (for heavy acceleration) and all points in between. Full-range oxygen sensors (used for the first time) provide essential information that allows the computers to properly regulate fuel delivery.


Diesel engines

All
diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...
s can be considered to be lean-burning with respect to the total volume, however the fuel and air is not well mixed before the combustion. Most of the combustion occurs in rich zones around small droplets of fuel. Locally rich combustion is a source of particulate matter (PM) emissions.


See also

* Engine knocking *
Hydrogen fuel enhancement Hydrogen fuel enhancement is the process of using a mixture of hydrogen and conventional hydrocarbon fuel in an internal combustion engine, typically in a car or truck, in an attempt to improve fuel economy, power output, emissions, or a combinat ...


Footnotes


Citations


References


"Advanced Technology Vehicle Modeling in PERE, EPA, Office of Transportation and Air Quality"
{{DEFAULTSORT:Lean-burn Engine technology