Lean Burn Lives

Improving fuel efficiency of engines, while maintaining their low cost and simplicity, has been largely ignored because of its difficulty.  No one knew this better than Michael Ward, Ph.D. Harvard, who pursued lean burn for 30 years.  Lean burn was seen as essential for fuel economy but was only partially understood until development of the 2-Stroke ICS engine. Lean burn, in its entirety, was solved through breakthroughs in ignition and engine design.

The Prototype CEI Ignition System

In an SAE paper 750348, GM showed that 150 mJ spark energy was required for lean burn. CEI confirmed this. However, Exxon claimed that high flow-velocities degraded lean burn (SAE paper 670467). Dr. Ward showed this to be incorrect. He showed that high flow-velocities enhanced lean burn, when a spark of 350 ma was used instead of a 100 ma. CEI developed an ignition with 5 times the energy and 5 times the flow-coupling capability with small coils of equal weight as state-of-the-art coils. The ignition also has 5 times faster rise time and charge time. During cold-start, for difficult-to-ignite fuels, i.e. ethanol and natural gas, it provides 10 times the energy for rapid start-up with low HC emissions.

Further improvements were made to the ignition with four patents granted in 2007.  The coil has a peak voltage of 42 kV, despite having 1/2 the turns-ratio of a conventional coil.  Two biasing magnets were used in the coil to give it the highest energy and efficiency. Halo-disc plugs with low-cost Tungsten-Nickel-Iron electrodes with much longer life, better coupling to the flow, and more intense sparks for more reliable ignition at all speeds and loads. They have circular spark gaps (don’t require indexing) and large gaps of 70 mil instead of 40 mil. Yet they have a lower spark firing voltage. The plug has a high capacitance of about 40 pF. It is truly “the spark plug that could save forests” according to the Economist.

The Prototype 2-valve, 2-plug, Squish-Flow, Lean Burn Engine

In 2000, CEI built a prototype, homogeneous charge 2-valve, 2-plug, lean-burn engine, which obtained a record leanness of over 30 to 1 AFR and 30% better fuel economy. See SAE Paper 2001-01-0548. Chrysler and Honda also used a 2-valve, 2-plug engine to set records in power and efficiency. Chrysler referred to the CEI Ignition in Design News “as the enabling technology for the lean burn engines of the future”.

The 2-Stroke Inverted Cross-Scavenged Engine

In 2009, we developed the perfect lean burn engine, with two provisional patents filed on May 22 and September 3, 2009.  It is the 2-Stroke ICS engine with two overhead valves and squish-flow, and two high energy halo-disc plugs, with an electronic fuel-injector. This engine requires only a new head and not a complete block, i.e. it has no ports in the engine block, and uses a standard engine block with an oil sump.  It is the only engine that uses the Miller cycle, ideally under all conditions, from an ER of 18 to 1 for the best efficiency and an effective CR of 10.4 for best power attained through valve closing (end of scavenging) at about 75º ABC.  By displacing the exhaust gases with fresh intake air, the process takes place at constant pressure and temperature, at NTP. It uses an ultra lean mixture with stratified charge for normal driving, except at cold-start and WOT when it needs a stoichiometric mixture. It uses an electrical supercharger during the scavenging time, to keep the intake pressure just above one atmosphere. The detailed design of the 2-Stroke ICS engine was recently successfully completed. It has the lowest cost and simplest structure, i.e. it is a small, low cost, light-weight engine with an unmatched efficiency and power.