Lean Burn Engine

Basically, engines which can operate in very lean air / fuel mixture are called "Lean Burn Engines". Japanese car makers, heading by Toyota, are the leaders in this technology.
Apparently, the leaner air / fuel mixture, the more frugal the engine is. But there are two reasons prevent conventional engines from operating in lean air / fuel mixture:


If the mixture is too lean, the engine will fail to combust.
Naturally, lower fuel concentration leads to less output.
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Lean burn engines avoid these problems by adopting a highly efficient mixing process. They use special shape pistons, with intake manifolds located and angled matching the pistons, the intake air will generate swirl inside the combustion chamber. Swirl leads to more complete mixing of fuel and air, thus largely reduce the badly-mixed fuel particles, which will not be burnt in conventional engines. This enables more complete burning, not only reduces pollutant, but also allow the fuel / air ratio to be lowered from 1 : 14 to 1 : 25 without altering output.
Today, Lean Burn technology has evolved into Direct Injection, which is basically the former added with direct fuel injection. Toyota, Mitsubishi and Nissan all concentrate in DI engines development.
Source- AutoZine Technical School - Engine

What is a lean-burn engine?

Lean-burn means pretty much what it says. It is a lean amount of fuel supplied to and burned in an engine's combustion chamber. Normal air-to-fuel ratio is on the order of 15:1 (15 parts air to 1 part fuel). True lean-burn can go as high as 23:1.

Lean-burn engines (both gasoline and diesel) enjoy higher fuel economy and cleaner emissions than conventionally tuned engines. By nature they use less fuel and emit fewer unburned hydrocarbons and greenhouse gases while producing equivalent power of a like-sized "normal" combustion engine. They achieve lean-burn status by employing higher combustion chamber compression ratios (higher cylinder pressure), significant air intake swirl and precise lean-metered direct fuel injection.
The downfall of lean-burn technology is increased exhaust NOx emissions (due to higher heat and cylinder pressure) and a somewhat narrower RPM power-band (due to slower burn rates of lean mixtures). Vehicles that use these types of engines require more complex catalytic converters and are often limited to light duty uses (passenger vehicles versus commercial trucks).

What is a Lean-Burn Engine - How does Lean-Burn Technology work

The Chrysler Lean Burn engine control system

Lean Burn Engine
What it is:
A lean burn engine is designed to operate with a very lean air-fuel ratio during light load conditions. Most modern gasoline engines are controlled to run at a chemically correct (stoichiometric) air fuel ratio (about 14.7:1) to make the three-way catalyst operate at high efficiency, reducing tail-pipe emissions. Lean burn engines mix more air with the fuel when full power is not needed, resulting in better fuel economy. Air/fuel ratio in lean burn engines can be as high as 22:1. When full power is needed, such as during acceleration or hill climbing, a lean burn engine reverts to a stoichiometric (14.7:1) ratio or richer.

How it works:
A very lean mixture of air and gasoline will not ignite as easily as a stoichiometric mixture when a spark is introduced. Several methods can be employed to achieve lean burn, including high temperature, high turbulence and stratification (high concentration of fuel vapor near the spark plug). Lean burn engines are often designed with high intake swirl to increase turbulence. Direct injection is one way to provide stratification. Since more air is taken in, the throttle plate can be opened wider for a given power, and losses associated with pumping are reduced. Lean operation also results in higher combustion efficiency and lower heat losses for better fuel economy. Note: Current three-way catalysts are designed to optimise NOx reduction at close to stoichiometric ratio. Lean burn engines generally cannot meet strict NOx emissions standards using three-way catalyst; additional NOx controls are necessary.

Customer benefit:
Better fuel efficiency without sacrificing engine power.

Industry status:
Under development.

NEW TECH: Lean Burn Engine

Lean burn
Lean burn is an internal combustion of lean air-fuel mixtures. It happens at very high air-fuel ratios (up to 65:1), so the mixture has considerably less amount of fuel in comparison to stoichiometric combustion ratio (14.6:1 for petrol).

The engines designed for lean burning can employ higher compression ratios and thus provide better performance, efficient fuel use and low exhaust 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 the large amount of NOx being generated, so a complex catalytic converter system is required. Lean burn engines do not work well with modern 3-way catalytic converters, which require a balance of pollutants at the exhaust port in order to carry out both oxidation and reduction reactions, so most modern engines run at or near the stoichiometric point.

Engines: Lean burn

Another file

http://cumminspower.com/www/literatu...eanBurn-en.pdf