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.


Chrysler Lean Burn computer

From the late 1970s to mid 1980s, Chrysler equipped many of its North American production cars with a spark control computer which it called the Lean Burn Computer on the large sticker on the unit.

Mounted on the air filter housing of most rear-wheel drive cars Chrysler produced during this time, it was responsible for adjusting spark timing based on manifold vacuum, engine speed, engine temperature and incoming air temperature; by doing this, Chrysler eliminated the traditional vacuum and centrifugal timing advance mechanisms used on distributors in order to provide more accurate spark timing. It also provided drive for the ignition coil directly, eliminating the separate ignition module.

Based on an early computer system, most Lean Burn computers were an open-loop emissions control system with no provided diagnostic port or "Check Engine" warning light, were difficult to troubleshoot, and were greatly responsible for the poor reliability reputation which dogged Chrysler at the time.

Many Lean Burn computers were replaced with the more reliable electronic ignition module and centrifugal/vacuum advance distributors used on earlier Chrysler vehicles, almost universally to improvements in fuel economy and driveability.


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 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 as much as 75% more air than theoretically needed for complete combustion into the combustion chambers. The extremely weak air-fuel mixtures lead to lower combustion temperatures and increased forced induction possibilities (that would otherwise be limited by high exhaust gas temperatures), leading to higher theoretical efficiencies when compared to engines running on a stoichiometric air-fuel mixture.


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 isn't equal throughout the cylinder. Instead, precise control over fuel injection 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 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. These were carburated 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 stratified charge (lean burn engines) will 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. That being the chemical stoichiometric ideal for complete combustion when averaging gasoline to be the petrochemical industries' accepted standard of C6H8.

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

* 1993–95 Civic VX
* 1998–2000 Civic Hx
* 2001 Civic Hx
* 2002–06 Civic Hybrid
* 2000–06 Insight


Diesel engines

All diesel engines are lean burning. This is essential to the way they ignite the fuel.

Ferox (fuel additive)

Ferox is a fuel additive. It was developed by Wesley Parish in 1985 from work done on experimental burn rate modifiers for solid rocket propellant systems used in the aerospace industry. Ferox was originally designed to lengthen the life engines. Until recently, it has been used predominantly in the marine, mining, and trucking industries. It is now used as a fuel additive in common automobile engines using gasoline, diesel, and others. The newest form is in a small tablet that is added with fuel into the tank to be dissolved.

There is evidence that ferox can lower polluting emissions, improve gas mileage, and reduce deposit build-up. There are also claims of prolonging engine life. However, the extent of these benefits for average fuel consumers is still not clear.

The product has been registered with the Environmental Protection Agency.

Ferox works as a catalyst, which lowers the activation energy of the rate determining step to break down build-up within the engine. This allows the carbon deposits to burn off at much lower temperatures.

Ten things that will increase the fuel economy of your vehicle

Ten things that will increase the fuel economy of your vehicle

Fuel prices surge upwards and show no sign of coming down, many people begin to wonder what can be done to save on fuel. there are a few things that can still be done to increase fuel economy. Here are ten things that you can do to save on fuel:

1. Filling up your tank properly.
This simply means try to avoid filling your tank to its maximum capacity. If the car becomes overheated, or if you are driving up a slope, then a tank which is filled to its maximum capacity will cause your fuel to drip onto the road where it can be dangerous (on rainy days, this will cause the road to be more slippery, and is a form of pollution).

On days where the temperature is high, try to fill your tank during the mornings or late afternoons where the temperature is cooler (since fuel will expand on hot days). This will allow you to have more fuel for your money, as well as preventing dangerous and costly run-off of wasted fuel.

2. Remove unnecessary weight from your car.
Did you know that for each 400 pounds that you carry in your car, this will mean 3-4 miles less that you can travel per gallon of fuel?

3. Amend your driving technique to increase fuel economy
• Drive at a conservative pace. If you vary your speed in anticipation of the road ahead you can save up to 25% of fuel. Make sure that any speed increases you make every time you press the accelerator are not cancelled out by having to slow down for a car in front of you, traffic light, or stop sign.

• Try to avoid making complete stops. By reducing your speed, rather than making a complete stop in anticipation of the traffic conditions ahead, you will be able to both conserve fuel as well as braking power.

• Start up slowly. When starting up from a complete stop, try to accelerate slowly. Accelerating at a conservative pace will carry you twice as much distance as racing ahead.

• Increase speed when approaching a hill. The temporary increase in speed will mean more momentum to push the car partially up the hill.

• Use downward momentum to your advantage. Rather than using the accelerator, use the downward momentum of your car to carry your vehicle further. However, only do this if it is safe to do so.

• Avoid having to change lanes frequently. When changing lanes, often you will need to accelerate to pass the car in front of you, and then use the slow down once you return to the lane. If done frequently, this can decrease fuel economy by up to 20-30%.

4. Use the air vents instead of windows.
Driving with open windows increase the drag on your car due to wind. This means the car will have to expend more power in order to move forward, and thus resulting in increased fuel consumption. Also avoid using the air conditioner if possible as this will also mean more fuel consumed.

5. Avoid warming up your car excessively.
Warming up your car in the morning means that you are using fuel to travel a grand total of 0 miles, and in the meantime also unnecessarily polluting the air around you.

6. Purchase a Hybrid vehicle.
Hybrid cars can clock upwards of 55 miles per gallon. This can often mean you will be able to increase fuel economy, and a possible monetary saving of around 25% - 35%.

7. Ensure that your tires are properly inflated.
Flat tires are a sure way to waste fuel as they can reduce the distance covered per gallon by as much as one mile.

8. Reduce wind resistance of your car.
A great way to do this is to make sure your car is waxed. This will allow wind to glide over your car easily, and thus reduce the drag on your vehicle.

9. Avoid using your car unnecessarily.
Driving with a cold engine can increase the amount of fuel consumed by as much as 60-70%, so try to make every trip count. In addition, by planning your trips, you may be able to cut down on the distance you will need to cover to do your shopping, get to work etc. Car pools are a great way to save on fuel going to work everyday.

10. Maintain your car regularly
The combined effects of the below suggestions will have a huge impact on the fuel economy of your car over time.

• Tune up your car regularly (especially the ignition system). A good tune-up by a qualified mechanic will save you fuel and extend the life of your vehicle.

• Make sure that the spark plugs are working properly (and that they are not misfiring). Misfiring spark plugs can possibly cost you 20% in mpg.

• Change dirty air filters (save 1 mph).

• Ensure your PCV valve is working appropriately.

• IMPORTANT: It is paramount that brakes are adjusted properly so that they do not drag along the wheel when your car is in motion. If your they are dragging along the wheel, then the car will demand more power when you are driving (to overcome the force of the brake). This can have major consequences in terms of fuel economy. To check that this is not happening to your car, jack up the tires and try to spin the wheel. If there is drag, then you will be able to feel it with your hand as you try to move the wheel.

E85 Risks

Corrosion

E85 can cause damage, since prolonged exposure to high concentrations of ethanol may corrode metal and rubber parts in older engines (pre-1988) designed primarily for gasoline. The hydroxyl group on the ethanol molecule is an extremely weak acid, but it can enhance corrosion for some natural materials. For post-1988 fuel-injected engines, all the components are already designed to accommodate E10 (10% ethanol) blends through the elimination of exposed magnesium and aluminum metals and natural rubber and cork gasketed parts. Hence, there is a greater degree of flexibility in just how much more ethanol may be added without causing ethanol-induced damage, varying by automobile manufacturer. Anhydrous ethanol in the absence of direct exposure to alkali metals and bases is non-corrosive; it is only when water is mixed with the ethanol that the mixture becomes corrosive to some metals. Hence, there is no appreciable difference in the corrosive properties between E10 and a 50:50 blend of E10 gasoline and E85 (47.5% ethanol), provided there is no water present, and the engine was designed to accommodate E10. Nonetheless, operation with more than 10% ethanol has never been recommended by car manufacturers in non-FFVs. Operation on up to 20% ethanol is generally considered safe for all post-1988 cars and trucks.


Water contamination

In addition to corrosion, there is also a risk of increased engine wear for non-FFV engines that are not specifically designed for operation on high levels (i.e., for greater than 10%) of ethanol. The risk primarily comes in the rare event that the E85 fuel ever becomes contaminated with water. For water levels below approximately 0.5% to 1.0% contained in the ethanol, no phase separation of gasoline and ethanol occurs. For contamination with 1% or more water in the ethanol, phase separation occurs, and the ethanol-water mixture will separate from the gasoline. This can be observed by pouring a mixture of suspected water-contaminated E85 fuel in a clear glass tube, waiting roughly 30 minutes, and then inspecting the sample. If there is water contamination of above 1% water in the ethanol, a clear separation of ethanol-water from gasoline will be clearly visible, with the colored gasoline floating above the clear ethanol-water mixture.

For ethanol contaminated with larger amounts of water (i.e., approximately 11% water, 89% ethanol, equivalent to 178 proof ethanol), considerable engine wear will occur, especially during times while the engine is heating up to normal operating temperatures. For example, just after starting the engine, low temperature partial combustion of the water-contaminated ethanol mixture takes place and causes engine wear. This wear, caused by water-contaminated E85, is the result of the combustion process of ethanol, water, and gasoline producing considerable amounts of formic acid (HCOOH, also known as methanoic acid and sometimes written as CH2O2). In addition to the production of formic acid occurring for water-contaminated E85, smaller amounts of acetaldehyde (CH3CHO) and acetic acid (C2H4O2) are also formed for water-contaminated ethanol combustion. Of these partial combustion products, formic acid is responsible for the majority of the rapid increase in engine wear.

Engines specifically designed for FFVs employ soft nitride coatings on their internal metal parts to provide resistance to formic acid wear in the event of water contamination of E85 fuel. Also, the use of lubricant oil (motor oil) containing an acid neutralizer is necessary to prevent the damage of oil-lubricated engine parts in the event of water contamination of fuel. Such lubricant oil is required by at least one manufacturer of FFVs even to this day (Chrysler).

For non-FFVs burning E85 in greater than 23.5% E85 mixtures (20% ethanol), the remedy for accidentally getting a tank of water-contaminated E85 (or gasoline) while preventing excessive engine wear is to change the motor oil as soon as possible after either burning the fuel and replacing it with non-contaminated fuel, or after immediately draining and replacing the water-contaminated fuel. The risk of burning slightly water-contaminated fuel with low percentages of water (less than 1%) on a long commute is minimal; after all, it is the low temperature combustion of water contaminated ethanol and gasoline that causes the bulk of the formic acid to form; burning a slightly-contaminated mix of water (less than 1%) and ethanol quickly, in one long commute, will not likely cause any appreciable engine wear past the first 15 miles of driving, especially once the engine warms up and high temperature combustion occurs exclusively.

For those making their own E85, the risk of introducing water unintentionally into their homemade fuel is relatively high unless adequate safety precautions and quality control procedures are taken. Ethanol and water form an azeotrope such that it is impossible to distill ethanol to higher than 95.6% ethanol purity by weight (roughly 190 proof); regardless of how many times distillation is repeated. Unfortunately, this proof ethanol contains too much water to prevent separation of a mixture of such proof ethanol with gasoline, or to prevent the formation of formic acid during low temperature combustion. Therefore, when making E85, it becomes necessary to remove this residual water. It is possible to break the ethanol and water azeotrope through adding benzene or another hydrocarbon prior to a final rectifying distillation. This takes another distillation (energy consuming) step. However, it is possible to remove the residual water more easily, using 3 angstrom (3A) synthetic zeolite pellets to absorb the water from the mix of ethanol and water, prior to mixing the now anhydrous ethanol with gasoline in an 85% to 15% by volume mixture to make E85. This absorption process is also known as a molecular sieve. The benefit of using synthetic zeolite pellets is that they are essentially comparable to using a catalyst, in being reusable and in not being consumed in the process, and the pellets require only re-heating (perhaps on a backyard grill, in a solar reflector furnace, or with heated carbon dioxide gas collected and saved from the fermentation process) to drive off the water molecules absorbed into the zeolite. Research has also been done at Purdue University on using corn grits as a desiccant. Once the ground corn becomes water logged, the corn grits can be processed much as the zeolite pellets, at least for a number of drying cycles before the grits lose their effectiveness. Once this occurs, it is possible to run the now water-logged corn grits through the natural fermentation process and convert them into even more ethanol fuel.


Air/Fuel mixture problems

Running a non-FFV with a high percentage of ethanol will cause the air fuel mixture to be leaner than normal in carbureted or open loop fuel injection engines, and cause closed loop fuel injection systems to adjust for the increase in oxygen content of the fuel mixture. A lean mixture, when leaner than stoichiometric, is unlikely to cause heat related engine damage because temperature decreases quickly once there is a surplus of air during the combustion event. The surplus air cools the burn, and lowers the exhaust gas temperature. The effects of surplus oxygen on the catalytic converter may be undesirable, and if too lean the engine will display roughness in operation. If the percentage of ethanol used results in sustained operation in the range between stoichiometric and best power mixture, problems may develop. In this range, between peak exhaust gas temperature and approximately 50 degrees rich of peak, combustion temperatures are at the highest possible, and may exceed the design temperatures for the engine. Detonation margins are reduced, and if operation at elevated temperatures is allowed to persist over considerable periods of time, heat related damage to valves and pistons can occur.

Without in-depth knowledge of the engine's mixture control system and instrumentation to monitor exhaust gas temperature, cylinder head temperature, cylinder pressure, and/or exhaust oxygen content, it is difficult to know whether the engine is operating in the "red" zone, or an acceptable mixture zone. Closed loop fuel injection systems eliminate much of the risk. This is also why the check engine light will illuminate if you mix more than around 50% to 60% E85 by volume with your gasoline in a non-FFV. If this happens, just add more 87 octane regular grade gasoline as soon as possible to correct the problem. (Some premium blends contain up to 10% ethanol; to correct the problem as quickly as possible, always add regular grade gasoline, not premium grade gasoline.) These fuel/air mixture related problems will not happen in a properly-converted vehicle.

Active Fuel Management

Active Fuel Management (formerly known as Displacement on Demand) is a trademarked name for the automobile variable displacement technology from General Motors. It allows a V6 or V8 engine to "turn off" half of the cylinders under light-load conditions to improve fuel economy. EPA tests show a 6% to 8% improvement in fuel economy, but real-world highway use promises even larger gains.

GM's current Active Fuel Management technology uses a solenoid to deactivate the lifters on selected cylinders of a pushrod V-layout engine.


Background

In the U.S., high-powered multi-cylinder internal combustion engines are perceived to be necessary to satisfy driver demands for quick acceleration, oversized vehicles and/or heavy towing capacity, but during daily use they are generally operated at power settings of less than 25%. For example, at freeway speeds, less than 40 hp (30 kW) are required to overcome aerodynamic drag, rolling friction, and to operate accessories such as air conditioning. Thus, a high-powered, large-displacement engine is highly inefficient and wasteful when being used for normal driving conditions- the vast majority of the time.

In general a Naturally-aspirated engine provides maximum power when the engine throttle is held wide open. When less power is needed, the throttle is mostly closed. As such the engine has to work to simply draw air through the throttle. The work that's done is called a "pumping loss". If some of the cylinders could be switched off, however, less air would be required, and the throttle held further open, thereby reducing pumping losses and increasing overall engine thermal efficiency. This is the motivation for cylinder deactivation.

In order to deactivate a cylinder, the exhaust valve is prevented from opening after the power stroke and the exhaust gas charge is retained in the cylinder and compressed during the exhaust stroke. Following the exhaust stroke, the intake valve is prevented from opening. The exhaust gas in the cylinder is expanded and compressed over and over again and acts like a gas spring. As multiple cylinders are shut off at a time (cylinders 1, 4, 6 and 7 for a V8), the power required for compression of the exhaust gas in one cylinder is countered by the decompression of retained exhaust gas in another. When more power is called for, the exhaust valve is reactivated and the old exhaust gas expelled during the exhaust stroke. The intake valve is likewise reactivated and normal engine operation is resumed. The net effect of cylinder deactivation is an improvement in fuel economy and likewise a reduction in exhaust emissions. General Motors was the first to modify existing, production engines to enable cylinder deactivation.


Second generation

The electronics side was improved greatly with the introductions of Electronic Throttle Control, electronically controlled transmissions, transient engine and transmission controls, engine emissions controls, and vastly increased computing power. A solenoid control valve assembly integrated into the engine valley cover contains solenoid valves that provide a pressurized oil signal to specially designed hydraulic roller lifters provided by Eaton Corp. and Delphi. These lifters disable and re-enable exhaust and intake valve operation to deactivate and reactivate engine cylinders. Unlike the first generation system, only half of the cylinders can be deactivated. It is notable that the second generation system uses engine oil to hydraulically modulate engine valve function. As a result, the system is dependent upon the quality of the oil in the engine. As anti-foaming agents in engine oil are depleted, air may become entrained or dissolve in the oil, delaying the timing of hydraulic control signals. Similarly engine oil viscosity and cleanliness is a factor. Use of the incorrect oil type, i.e. SAE 20W40 instead of SAE 5W20, or the failure to change engine oil at factory recommended intervals can also significantly impair system performance.

In 2001, GM showcased the 2002 Cadillac Cien concept car, which featured Northstar XV12 engine with Displacement on Demand. Later that year, GM debuted Opel Signum² concept car in Frankfurt Auto Show, which uses the global XV8 engine with displacement on demand. In 2003, GM unveiled the Cadillac Sixteen concept car at the Detroit Opera House, which featured an XV16 concept engine that can switch between 4, 8, and 16 cylinders.

On April 8, 2003, General Motors announced this technology (now called Active Fuel Management) to be commercially available on 2005 GMC Envoy XL, Envoy XUV and Chevrolet TrailBlazer EXT using optional Vortec 5300 V8 engine. GM also planned to extend the technology on new High Value LZ8 V6 engine in some 2006 mid-size passenger cars. In both designs, half of the cylinders can be switched off under light loads.