Sonex Combustion System (SCS) for in-cylinder control of ignition and combustion to permit gasoline engines to run on safer diesel-kerosene-type “heavy fuels” for use in military and commercial applications such as Unmanned Aerial Vehicles (UAVs)
SCS cylinder head design and Cold Starting System (CSS) for two-stroke, spark-ignited (SI) engines
SCS heavy fuel conversion maintains the gasoline engine’s stock carburetion or fuel injection system, intake and exhaust systems, SI system, compression ratio and lightweight
SCS HFEs™ running on heavy fuels JP-5, JP-8 and D-2 diesel (with lubricant additive for all fuels) retain the precision ignition of the SI process and knock-free combustion
SCS HFEs achieve equal or reduced fuel consumption (18% to 28% less at cruise rpm)
Cold starting to -20°C
New two-stroke, SI, HFE design from Sonex partner ACE Technologies features cylinder balancing, higher power, intelligent ECU controls, integrated failsafe
SCS HFE embodiments in the cylinder head of two-stroke engines provide control of fuel vaporization late in the compression stroke such that a portion of the heavy fuel is then vaporized near the spark plug. As the combustion event progresses it causes the fuel to fully vaporize and combust. The SCS heavy fuel conversion maintains the gasoline engine’s stock carburetion or fuel injection system, intake and exhaust systems, spark ignition system, compression ratio and lightweight. SCS HFEs running on heavy fuels JP-5, JP-8 and D-2 diesel (with lubricant additive for all fuels) retain the precision ignition of the SI process and knock-free combustion. Compared to operation on gasoline, these HFEs achieve equal to or reduced fuel consumption (18% to 28% less at cruise rpm) and produce no visible smoke.
Disassembled SCS Two-Stoke HFE Components, from left to right:
Combustion chamber inserts containing SCS design embodiments, Cylinder head, including glow plug heater, and
Cylinder body with stock head removed
The Sonex CSS comprises a patented heated fuel vaporizer and a solid state control module.
The SCS cold starting system uses a compact, electrically powered subsystem to vaporize the heavy fuel for cold starting. Once the engine has been started, the starting system is automatically disabled.
A version of the Sonex CSS developed for the Insitu ScanEagle is shown in the figure below:
Sonex is scaling its small, two-stroke engine cylinder head insert design concepts as a regenerative technology for augmenting in-cylinder temperature to enable viable sustained auto-ignition. The Sonex proprietary (patent pending) Regenerative Heat Retaining Element (RHRE) design is being tested for use in natural gas fueled engines. The RHRE is a passive retrofit combustion chamber insert designed to retain thermal energy from one combustion cycle to the next that in turn conditions the fuel in-cylinder for ignition and reduces the fuel required. This ignition event yields an initial stable kernel of combustion that rapidly expands as evidenced by rate of heat release calculated from pressure traces from
in-cylinder transducer measurements.
The RHRE is expected to reduce pollutant emissions, save fuel, cut operating & maintenance costs, and increase horsepower. Engine test results confirm these improvements running on gaseous fuels: combustion stability (typically 15 to 30% better), pollutant emissions (17% to 45% lower), fuel consumption (3% to 8% less) and HP (4% to 23% higher).
Sonex has adapted the SCS heavy fuel technology for use on a commercially available portable generator powered by a four-stroke engine for military and commercial applications. Sonex applied the experience gained from developing the SCS HFE technology for small two-stroke engines in adapting its CSS to the heavy fuel conversion of a small single cylinder, four-stroke, SI, gasoline engine powering a commercially available small gasoline fueled generator.
Sonex designed and fabricated enhancements to engine-generator subsystems for integration into advanced prototype, 1 kW, JP-8 fueled, single man portable, generator set.
The SCS improves the combustion of fuels in four-stroke, direct injected (DI) engines through design modification of the pistons to achieve chemical/turbulent enhancement of combustion. The patented SCS piston design produces, retains, and expels chemical auto-ignition aids to cause controlled compression ignition after top-dead-center of the compression stroke in response to timed direct injection of the fuel.
The SCS for DI engines is based on patented piston designs containing micro-chambers (MC) which provide an in-cylinder method for isolating and capturing a small portion of an unthrottled air-fuel charge in each combustion cycle. These MCs form a segmented ring around the piston bowl, with each MC positioned relative to a fuel injector spray. The MCs are connected to the piston bowl by tunnel-like vents arranged strategically so that a fraction of the fuel can be trapped in the MC. The flame from the main chamber is quenched in the vent passage, preventing complete combustion in the MCs. Only slow and incomplete oxidation (of the trapped fuel) takes place, resulting in the formation of highly reactive radicals and intermediate species.
Sectional View of Sonex Piston for Direct Injected Engines
Per Sonex U.S. Patent Number 5,862,788
(2) Conversion of four-stroke gasoline engines to heavy fuel operation using a sparkless ignition process
Sonex has developed a process for the conversion of four-stroke gasoline engines to burn heavy fuels using a proprietary sparkless ignition process while maintaining moderate cylinder pressures to assure lightweight construction; this combustion process is call Sonex Controlled Auto Ignition (SCAITM). The SCS SCAI method for four-stroke engines is based on unthrottled air induction, direct fuel injection, and low to moderate compression ratio (<12.5:1).
The patented SCAI piston design produces, retains, and expels chemical auto-ignition aids to cause fully controlled compression ignition after top-dead-center of the compression stroke in response to timed direct injection of the fuel. Significantly, all the fuel is delivered to the piston bowl and mixed with the air during the latter portion of the compression stroke. Ignition occurs simultaneously at a high rate throughout the combustion volume after completion of injection. The SCAI operates over the full range of rpm and loads. The multi-fuel SCAI operates at reduced peak cylinder pressure to enable lightweight engine design.
SCAI enables precise control of auto-ignition, combustion and peak cylinder pressures with single phase controllable rates of heat release for a variety of fuels, since SCAI is not fuel dependent. The fuel and air captured in the MCs produce reactive chemical species that are carried over to cause sparkless compression ignition in the next cycle at moderate compression ratios. In-cylinder fuel injection timing provides engine performance control of peak cylinder combustion pressure, thereby assuring lightweight engines. The Sonex pistons enhance in-cylinder turbulence via the MCs and vents to promote particulate reduction during the power stroke.
The SCAI sparkless, fully unthrottled, compression ignition combustion process was advanced on kerosene-based heavy fuel from late 2002 to late 2007 under an agreement with the Defense Advanced Research Projects Agency (DARPA) for the development of a multi-cylinder, four-stroke, HFE combustion process for potential DoD applications. In 2007 Sonex successfully demonstrated to DARPA the laboratory SCAI engine operating on JP-8 heavy fuel at power levels up to 250 hp with significant reductions in fuel consumption when compared to a gasoline engine. In addition, exhaust emissions were reduced, validating the potential of the patented piston embodiments to manage levels of emissions in-cylinder. The fully lean-burn SCAI process was run with full control over the entire operating range to 4,500 rpm, which is essential to a wide range of applications on any fuel.
(1) Lean-burn, piston-based combustion process for the automotive market to cost effectively improves fuel mileage 25% to 30% and reduces emissions for gasoline direct injected (GDI) engines
Sonex Controlled Auto Ignition (SCAITM), which is considered a lean-burn combustion process, has significant potential for commercial application in the automotive market for GDI engines to cost effectively improve fuel mileage 25% to 30%. In addition to the improvement in fuel mileage, the ultra-low exhaust emissions of the SCAI lean-burn combustion process qualify it as a “green” technology. See Technical Note No. 2017-10-12 on Controlled Radical Ignition and Flameless Combustion
Sonex is pursuing commercialization of the SCAI-GDI application through a joint marketing and licensing agreement with Lean-Burn Combustion, Inc. (“LBC”), a start-up entity based in Alexandria, Virginia. LBC was formed by Michael I. Keller, the consultant who serves as the part-time Director of Business Development for Sonex.
(3) Reduction of particulates in direct injected diesel engines
The SCS Low Soot Diesel Design (LSDD) enables soot and oxides of nitrogen (NOx) reductions in standard DI diesel engines at compression ratios greater than 16:1. With LSDD the design emphasis is in placing the vents (with their high velocity jets) for maximum interaction with the soot cloud in the piston bowl. During the power stroke, the pressure drops in the combustion chamber more rapidly than in the MCs, and highly reactive gases are expelled from the MC at high speeds into the soot cloud. In addition, the soot level remains at a reduced level when high levels of exhaust gas recirculation (EGR) are used to reduce NOx. The LSDD has been shown to be completely different and more effective than an air cell. Sonex LSDD experience with multi-cylinder turbo-charged engines shows an overall cycle soot reduction of 50% and an accompanied 10% reduction in NOx (without EGR). Significant reductions in NOx can be achieved with common rail ECU control of injection timing and EGR while holding the soot level at the reduced level. Ricardo Consulting Engineers in Europe presented results of their evaluation of a major OEM engine with pre-production OEM LSDD pistons, a computation fluid dynamic (CFD) and gas dynamic analysis at the SAE Fuel and Lubes, May 2002 Conference: SAE 2002-01-1682.