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MAHLE-led consortium’s micro-CHP CNG engine provides 20% efficiency boost over current market best

Tests have demonstrated that a residential combined heat and power (CHP) engine developed as an Advanced Research Projects Agency - Energy (ARPA-E)-backed venture through the Generators for Small Electrical and Thermal Systems (GENSETS) program (earlier post) offers at least a 20% improvement in efficiency over the current leading alternatives.

The single-cylinder engine, which runs on natural gas (NG), has been developed by a consortium led by MAHLE Powertrain. It features the specialist’s low friction technology and manufacturing techniques, including the new MJI (MAHLE Jet Ignition) pre-chamber ignition technology, which is already being demonstrated in automotive applications.

ARPA Engine 4

Jet ignition is a pre-chamber-based combustion system that enables enleanment beyond what is achievable with traditional spark ignition engines. MJI extends traditional limits of lean combustion to maintain lower gas temperatures and therefore reduce harmful NOx formation.

The enleanment capabilities of the 390 cc single-cylinder engine are extended from λ = 1.6 to λ = 2 with the incorporation of auxiliary fueling in the pre-chamber. As the engine is enleaned beyond λ = 1.6, fuel is injected into the pre-chamber. The engine utilizes PFI for the main chamber and direct injection for the pre-chamber auxiliary fuel.

A major benefit of the additional enleanment is a further 93% reduction in engine-out NOx between the two lambdas.

MAHLE Powertrain is supported in the project, which was announced in November 2015, by Oak Ridge National Laboratory, Louthan Engineering, Kohler Company and Intellichoice Energy.

Electricity generated at the point of use is an effective way of combating the inefficiencies of centrally produced power. CHP motors are a perfect solution for generating electricity and harnessing otherwise wasted energy for heating, for both primary power and heat generation or for use on an ad hoc basis during power outages. However, this technology has previously been cost prohibitive, inefficient and displayed suboptimal reliability characteristics. In testing, the 1 kWe micro-CHP motor achieved 33% Electrical Conversion Efficiency; 20% more than the current leading unit in this power class.

—Mike Bunce, Head of Research for MAHLE Powertrain LLC and Principal Investigator on the project

Further, simplicity of design and manufacturing will reduce cost and increase durability.

Downspeeding is a technique that, alongside downsizing, has brought significant efficiency benefits to the automotive and commercial vehicle markets. Alongside MJI, this has been the key to increasing efficiency of the new ultra-lean motor. The ability to efficiently generate and harness residential power represents a huge opportunity to help make our country, and planet, cleaner. The incremental benefits brought by evolving technologies help make CHP motors a more viable solution, which hopefully inspires a greener outlook that encourages the next steps towards an ultra-low emissions goal.

—Mike Bunce

In a paper presented on an aspect of the work at WCX SAE World Congress Experience this year, Bunce and his colleagues noted that while the primary intended application for the engine is stationary power generation, it is possible ultimately to extend the concept to automotive range extender applications as well given the similar two-valve configuration and cylinder displacement.

MAHLE’s low friction expertise has been crucial for delivery of the GENSETS project. The final design incorporates a wide range of the company’s commercialized technologies, including its Evotec II piston, which is an award-winning, lightweight component to encourage enhanced efficiency. Finally, low temperature lean aftertreatment helps meet expectations for reduced emissions.


  • Peters, N., Bunce, M., and Blaxill, H. (2019) “The Impact of Engine Displacement on Efficiency Loss Pathways in a Highly Dilute Jet Ignition Engine,” SAE Technical Paper 2019-01-0330 doi: 10.4271/2019-01-0330



Way too late in the cycle of innovation to be considered, just another ICE polluter, albeit more efficient.


There are situations when this could be very useful.

I wonder is there anything there that could be used in a range extender ?

I suppose the two applications are very different - in the CHP thing, you aren't so worried about generating heat - as long as you capture it, while a range extender should just be as efficient (in a narrow revs band) as possible.


Quote Lad: "Way too late in the cycle of innovation to be considered, just another ICE polluter, albeit more efficient"

Absolutely incorrect. The North East corridor of the United States consumes copious amounts of energy heating homes, businesses and buildings. In fact, compared to power generation and travel, heat is by far, the number one consumer of energy there. Any well designed CHP system meets the efficiency of the best furnace, and coupled with a heat pump, can far exceed it.

Short of nuclear powerplants, we will be consuming natural gas for energy. Might as well do it efficiently.

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