Lean Burn Lives

Summary - Engines

The high speed, high compression, lean burn, fast burn engine is the most efficient and cleanest engine under normal driving conditions. We can view the 4-stroke engine as the low-tech version of this engine, and the 2-Stroke as the high-tech, idealized version of this engine. If some of difficulties the 2-stroke can be overcome, it can be shown to be vastly superior to the 4-stroke. This has been finally accomplished, in the context of the idealized lean burn engine. A feature never envisioned for the 2-stroke is having two overhead valves without the need for ports in the engine block. Called the 2-Stroke Inverted Cross-Scavenged engine, it is a revolutionary design, leading to a perfected lean burn engine.

  The 2-Stroke ICS engine operates under two modes: at light loads, as a stratified charge, lean burn engine; and at high loads, as a homogeneous charge, stoichiometric (14.7:1) air-fuel ratio.  With the help of the 3-way catalyst, it has low emissions under both modes.  It has a hot intake to insure high efficiency and low emissions at cold-start; and a cold intake to maximize power.  Relative to the Diesel, it is far superior on all counts, and relative to the hybrid and EV, it is superior in terms of cost, power and efficiency (see the Home page).  

The Diesel has three limitations relative to the gasoline engine. Firstly, it is less powerful because it cannot utilize all the air it breathes, i.e. it cannot  inject, mix, and burn fuel near top center, and therefore cannot operate at 14.7 air-fuel ratio for power, and for use of the 3-way catalyst. Second, it is no more efficient than a well-designed gasoline engine operating ultra-lean. Thirdly, the diesel is more polluting, expensive, complex, heavy and underpowered.

The Hybrid’s main advantage is its apparent high efficiency and low emissions. Its main and obvious disadvantage is high cost.  It was recently pointed out that average cost increase of the hybrid is $5,000 and of a plug-in hybrid (EV) is $10,000 over a standard car. The typical car buyer would not make the necessary investment on the hybrid or EV unless they could recover their investment in three years. This is impractical unless gas sells for over $10.00/gal.

The Optimized CEI Ignition and the two-valve Ward/May engine.

In 2008, two provisional patents were filed on the ignition and on the Ward/May engine. One year later, they were converted to U.S. patents. The ignition has an energy density greater than 1 mj/gm.  The engine has only two valves, a SOHC, a combustion chamber mostly under the exhaust valve, like the Fireball, which has a high efficiency gain of 40% and a high compression ratio (Automotive News, No. 6, 1984). But unlike the May Fireball, the Ward/May engine has no problem handling the very lean mixture with its ignition and long-life halo-disc plugs. 

The 2-Stroke Inverted Cross-Scavenged Engine.

In May, 2009, a provisional patent was filed on the 2-Stroke ICS engine.  The design is revolutionary in that it has two overhead valves, an intake and exhaust valve, and is the first 2-stroke engine which does not require ports in the engine block (has an oil sump, like a  normal 4-stroke engine). This is a tremendous advantage, and can use almost any block. The intake is always above one atmosphere, which forces oil in the head not to leak into the combustion chamber at light loads (a problem encountered with the experimental, 4-stroke, single-cylinder engine). The engine uses a CEI ignition with two halo-disc plugs and a state-of-the-art electronic fuel injector, as was used in the Ford PROCO.  It uses a Miller Cycle with a CR, e.g. of 15:1 (or greater) for an effective CR of 10:1, and a small Electric Supercharger on the intake.

A car with the 2-Stroke ICS would cost less than half of a hybrid and have an efficiency comparable to the hybrid’s.  And it would be simple to build and maintain.  Since it is truly a two stroke engine, it would have twice the power, all other things being equal.  While we can build a single cylinder prototype, a car engine can be made in collaboration with a car maker.   It can have two cylinders, like the Fiat 500, but would be much more efficient and powerful. By working with Chrysler-Fiat and its new leadership, we can prototype the world’s best car.   By incorporating Michael May’s combustion chamber in the 2-Stroke ICS design, it would have a lowest cost, simplest design Lean Burn engine with the highest efficiency and power.

A SECOND CUT AT DESIGN PARAMETERS OF THE 2-STROKE ICS ENGINE, COMPLETED 9/30/2009

The exhaust valve timing

Opening time: 150º after top center (ATC)

Closing time: 75º after bottom center (ABC).  Duration ΔΘ = 105º

The intake valve timing

Opening time: 150º ATC, a single cam operating both valves.

Closing time: 75º ABC.  Duration same as above  ΔΘ = 105º

Compression Ratio = Expansion Ratio = CR0 = ER0 = 18 to 1

Effective CR ≈ 0.58 * CR0 = 10.4 to 1 

Effective ER = (150º/180º) · 18 = 15 to 1

Fuel Injection Timing

Start of injection: 75º ABC

Typical end of injection: 90º BTC.   Duration = 15º

The major timing events

1. Expansion [0º to 150º ATC]; Duration = 150º

2. Blowdown [150º ATC to BC]; Duration = 30º

3. Scavenging [BC to 75º ABC]; Duration = 75º

4. Compression [105º BTC to TC]; Duration = 105º.  Total duration = 360º

The minor timing events

1. Fuel injection [105º to 90º BTC typically]

2. Ignition [30º BTC to TC]

3. Electric Supercharging [BC to 75º ABC] at Intake.

Typical engine dimensions

Bore = 3.5”; Stroke = 3.0”; Fuel injector diameter = 0.5”; CR0 = ER0 =18 to 1

Valves = 1.0” [actual size] + 0.5” [outer margin]

  Squish Lands are about 0.050” at TC; Intake valve is about 0.050” at TC

Michael May combustion chamber; Exhaust valve is ≈ 0.5” x 1.5” at TC.

 

Below are shown two cross-sections in planes including the two valves [intake and exhaust] of a typical maximum Scavenging period and the Fuel Injection period of the 2-Stroke ICS engine. Underneath are shown 1) a cross-section of the Cylinder Head with a pair of halo-disc spark plugs with small, high energy optimized coils with the two valves and the central fuel injector; and 2) a cross-section of a two-cylinder 2-Stroke ICS engine.

Note that power is controlled by a Speed/Density map as in a conventional engine, where Density is proportional to the manifold absolute pressure MAP (~ fuel injection Time), except that our case it is proportional to the degree of Stratification, which is also proportional to the Volume of injected fuel, i.e. to the fuel injection Time (and to a lesser degree to the mixture equivalence ratio). That is, during the scavenging period, the intake pressure is approximately 1 atmosphere, and the way to vary power during the light load case is to vary the level of injected fuel so that, to first order, different volumes of combustible mixture are made available in the center-most part of the combustion chamber (see the figure, below and to the right).