Merritt Unthrottled Spark Ignition Combustion Explained. Or Not.
Green Car Congress reports on a recent test of the Merritt Unthrottled Spark Ignition Combustion (MUSIC) engine by Powertrain Technologies. "MUSIC is an un-throttled, high thermal efficiency, lean-burn, spark ignition system that uses an indirect combustion chamber to produce charge stratification by means of controlled air management" the unelected reporters reveal. In laypersons terms, a trick cylinder head with an external combustion chamber and twin injectors were fitted to a 2.0 Ford Duratec engine, allowing more efficient fuel-air mixtures and (diesel-like) unthrottled operation from idle to full load. There's no sense in trying to break down the technology any further, because it's complicated enough to make HCCI look like the Flintstone car. The upshot: the MUSIC engine delivered 20 percent better efficiency than a standard Duratec in the urban cycle, with an even better 42.5 percent improvement at near idle speeds. The downside? Power is cut nearly in half, delivering only 50 hp (from a two liter engine) at 4k rpm. Developers claim their results could improve with better injection equipment, but add the cost and reliability issues and you have a yourself a hefty engineering to-do list before this technology hits the streets.
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If this is direct injection, then it would be easy to convert it to a 2 cycle with no pollution issues and you get your 50% power loss back with a power stroke every 360 degrees.
Some myths which appear to have evolved about this engine: The MUSIC engine (now branded the Pure Burn engine) was always capable of meeting and exceeding the power output of an equivalent diesel engine. The power outputs posted in the test results were those compliant with a NEDC Urban Driving cycle which only required power outputs up to 5.5 BMEP at 4000rpm. The engine itself was capable of 9.0 BMEP at 6000rpm (90kW/litre prior to friction loss). The second fuel injector was an experimental suggestion; it was proven to be unnecessary and was never used for the 4-stroke Duratec prototype and is not part of the patented technology. The NOx output of this engine was tested at 10mg/km, compared to the latest Euro 6 limits of 80mg or 60mg for diesel and petrol engines. This incredibly low emission is due to the enormously fast and complete combustion, yet within a low average chamber temperature due to the inner vortex of excess intake air. There was vocal opposition and misinformation from diesel car and component manufacturers at the time (including the catalytic converter industry). Now that they are hamstrung by the latest NOx and particulate scandals we wait and see if any of them re-consider their positions. I declare my interest - I am a director of Pure Burn Engines Ltd.
To clarify my previous posting: - more than merely being "capable" of 9.0 bar IMEP @ 6000rpm, it was actually tested to deliver that power by Cosworth Engineering in March 1996, and for which we have an affadavit signed by their Chief Engineer John Hancock. - NOx output was measured on a testbed at Coventry University at 10-30ppm (compared to many 1000s on a traditional engine) and so our road emission estimate quoted above is probably too high. Unfortunately we haven't yet got a vehicle demonstrator to produce road test data. This is our prime objective. - allegations of complexity, and comparisons with IDI and HCCI engines are not supportable. The Pure Burn Engine cylinder head conversion has no moving parts, and only requires one injector per cylinder. All the environmental and power benefits are derived from the interior formed shape of the auxiliary combustion chamber, and corresponding reprogramming of the ECU. Please visit our new website www.pureburnengines.co.uk for up-to-date information on this engine which is poised to make diesel redundant in the passenger car market.