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Test of MUSIC Engine Shows 20% Improvement in Fuel Economy Over Conventional Gasoline Unit
17 May 2008
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| MUSIC engine on the test bed. |
Recent testing of a 2.0-liter, four-cylinder implementation of the Merritt Unthrottled Spark Ignition Combustion (MUSIC) engine, initially developed at Coventry University, (earlier post) showed a 19.8% improvement in fuel economy compared to a baseline Ford 2.0L Duratec.
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.
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| Side view of the MUSIC cylinder head. Click to enlarge. |
During the compression stroke, the piston forces air to spin around the periphery of an external cylindrical combustion chamber with a strong forward bias towards the far end of the chamber where the spark plug is situated, thereby creating a helical swirl motion. This helical swirl motion has the effect of stacking layers of rotating gas so that air delivered early in the compression stroke is situated near the spark plug end of the combustion chamber and remains in this location throughout the compression stroke.
The external chamber is connected to the combustion cylinder by an orifice large enough to minimize the pumping losses associated with the gas transfer. The orifice forces air to emerge as a powerful jet as it enters the combustion chamber. The velocity, density and temperature of the air in the jet all increase during the compression stroke. A gasoline direct injection (GDI) fuel injector delivers gasoline, or other fuels, directly into the air jet emerging from the orifice.
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| MUSIC system schematic. Click to enlarge. | Cylinder head design layout and prototype for the four-cylinder engine. Click to enlarge. |
Fuel delivered early on in the compression stroke finds its way to the spark plug end and remains there, as an ignitable mixture, ensuring spark ignition, even when air with no fuel follows after the fuel injection stops. The formation of a stratified charge keeps the fuel/air mixture separate from air with no fuel in this way, while ensuring a very rapid vaporization of injected fuel. This allows MUSIC to operate completely unthrottled from idling to full load.
Timing of the beginning of fuel injection controls the local mixture strength in the cylinder, enabling exact control over local mixture strength by the formation of a pre-vaporized stoichiometric air/fuel mixture situated near the spark plug irrespective of engine speed or load. It also enables the ignition of lean mixtures which are formed later on during the fuel injection process.
The air mass flow through the orifice varies considerably during the compression stroke, increasing towards the end of the stroke. The GDI fuel injector, which can deliver at a constant rate, can form a stoichiometric mixture if it injects fuel at the crank angle position when the air mass flow rate through the orifice is some 14.5 times greater than the fuel mass flow rate through the injector.
This mixture—the Primary Mixture—will be stratified near the spark plug and there readily ignite when the plug energizes. If fuel injection continues for a longer duration after the formation of the Primary Mixture, a lean fuel/air mixture will be formed. This will be ignited by the flame produced by the combustion of the adjacent Primary Mixture. The timing of fuel injection start needed to form the Primary Mixture is advanced with engine speed to ensure that a stoichiometric mixture is formed, now at an earlier crank-angle position, as the air mass flow rate in the orifice increases with engine speed.
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| A sample strategy for using both injectors to meet higher engine loads. At a higher speed of 4000 rpm, the Power Injector (injector-2) is activated for its full duration as soon as the air jet intensity becomes large enough. The combined delivery of fuel from both injectors and their relative timing will enrich the mixture according to the driver’s demand for BMEP. Note that injector-2 is shown delivering into the cylinder after TDC in order to provide some fuel for the air in the bump clearance at TDC. Also note that the ignition of the fuel mixture produced by injector-2 is brought about by the fuel delivered earlier by injector-1, first to the spark plug and then to the Primary Zone Mixture. Click to enlarge. |
To achieve high loads, MUSIC needs to deliver fuel to the air jet until the end of the compression stroke when the air mass flow is very rapid and time is short. A second fuel injector—the Power Injector—is used for this with a larger fuel flow rate capacity.
The Power Injector injects axially into the air jet when the air is hot and dense, so enabling rapid vaporization over the available short time period. The Power Injector can also deliver some fuel to the air contained in the bump clearance above the piston at top dead center at the end of the compression stroke. It may be possible to incorporate the functions of the two injectors into one complex injector but the cost and complexity of such an injector may exceed the cost of two simple solenoid injectors that are currently mass-produced, according to MUSI Engines Ltd.
Unlike gasoline direct injection (GDI) engines, which rely on fuel being delivered to the spark plug at the very end of the compression stroke, when most of this fuel remains as a suspension of liquid droplets, MUSIC delivers to the spark plug a homogeneous air/fuel mixture produced at the start of the compression stroke and stratified at the spark plug end, enabling rapid ignition at all engine speeds, according to the inventor, Dr. Dan Merritt.
Implementing MUSIC requires a modified cylinder head and a direct injection fuel system. The indirect combustion chamber features an inbuilt helical swirl that can not only run successfully at air/fuel ratios of more than 100:1 but also reduces HC and NOx emissions significantly. The developers earlier estimated that up to 80% reduction in NOx and HC is possible. Load and speed control is achieved by the precise control of injection timing and duration.
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| Results taken on the first test run of the MUSIC Engine constructed by Powertrain Technologies. CLick to enlarge. |
The four-cylinder prototype is based on a cylinder head mounted on a Ford Duratec crankcase. The MUSIC system does not require any new supporting technology. Apart from the MUSIC cylinder head designed to promote the new combustion system invented by Dr. Merritt, the prototype engine uses currently available production components throughout.
To fit the MUSIC cylinder head, the design team at Powertrain Technologies Ltd had to work around existing fixed features such as the head bolts and the coolant and oil transfer passages. To make the 4-cylinder as versatile as possible, the key design features—the helix that generates the air motion; the transfer port plus the spark plug; and the injector locations—had to all be removable for revised designs.
Powertrain Technologies Ltd developed the test engine with the aid of a grant from the UK’s Energy Saving Trust. The 20% improvement was calculated over a number of test points in the NEDC urban cycle. The thermal efficiency increases as the engine load decreases and at near idling condition the fuel saving measured was an 42.5%.
Andrew Barnes, the Managing Director of Powertrain Technologies, expects that, in view of these results obtained at such an early stage of development, up to 25% improvement in fuel economy can be achieved in the near future.
Due to difficulties in obtaining suitable injection equipment we were unable to optimize the engine at certain test conditions, we are confident that there are a few more percentage points available when optimized.
—Andrew Barnes
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May 17, 2008 in Concept Engines, Engines, Fuel Efficiency | Permalink | Comments (21) | TrackBack (0)
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Comments
20% improvement? I'm reserving judgement until more informed sources chime in.
Anyone? Anyone?
Posted by: DieselHybrid | May 17, 2008 10:52:55 AM
This looks promising--nothing particularly exotic, an incremental improvement of existing ICE technology, so it looks like something that could be mass-produced near term. But what's the improvement compared to a more mainstream DI engine? How would it compare in cost and efficiency to Ford's own 'eco-boost' turbo direct-injected engines?
Posted by: Nick | May 17, 2008 11:05:29 AM
My primary concerns would be the pumping losses from the orifice and the thermal losses. That's coming from an armchair engineer, so.... take it for what it's worth.
A big downside to the engine is that it requires (if I read properly) TWO GDI injectors per cylinder. This would increase the cost of the engine. By how much, I do not know.
If this was used in conjunction with turbo charging, downsizing, and mild hybridization we could see real world 30-40% fuel economy improvement.
Make the vehicle a little lighter, more aerodynamic, and use low rolling resistance tires..... whoever thinks that the 35mpg CAFE standard is unachievable is small minded.
Posted by: GreenPlease | May 17, 2008 11:48:39 AM
42% efficiency is quite an achievment indeed for a gazoline engine, could be even better adding an Atkinson cycle, it requires 2 injectors per cylinder but the trend is to move to less cylinder, PSA just started teh development of 3 cylinders one liter engine that would deliver 100HP. The appealing thing is that is needs no new technology or material, or retooling. Compare to main stream DI it pushes the concept of stratified load furter then allowing leaner burn and no throttle, main stream DI claim 10 % improvement. Also apparently the NOx is reduced too when it is a significant problem on main stream DI.
Posted by: treehugger | May 17, 2008 12:07:15 PM
Rafael - where are you ??
Posted by: mahonj | May 17, 2008 3:46:14 PM
mahonj,
click to the following link to see Rafael's, mine and opinion of others on this subject.
http://www.greencarcongress.com/2007/09/results-of-musi.html
I still think that this is a promising concept, that, when combined with cooled EGR at higher load to reduce NOx for use with 3-way catalytic converter, will produce an ICE with diesel-level efficiency at GDI cost. See my posting on the previous article on this subject.
Posted by: Roger Pham | May 17, 2008 8:01:57 PM
A three inline cylinder engine combined with a turbo would make a great downsized engine, and only require 6 injectors.
Posted by: GdB | May 17, 2008 9:45:33 PM
It doesn't say 42% efficiency. It says 42% fuel saving at near idling, which is not surprising considering the pumping losses.
Posted by: globi | May 18, 2008 1:39:48 AM
Enlarge the table the article and you will see that it shows a maximum efficiency of 42.90% at 2500 rpm and a power of 22.91 kWh.
Posted by: Anne | May 18, 2008 5:57:21 AM
I think before they jump to their conclusions. They should put several of these engines in actual cars and drive each them in real driving conditions for 100,000 miles. Then compare them to other types of auto engines.
Posted by: garth | May 18, 2008 7:27:07 AM
This is nice, but, the technology cuts the original horsepower in less than half. I wonder if this is because they were demonstrating extremely high AFRs and if they could run the engine closer to Stoich.
Posted by: mark | May 18, 2008 10:20:29 AM
Specific power? Can such an engine rev up like a normal gasoline engine, or does it have to be larger for equivalent horsepower, much like a diesel?
Posted by: Nick | May 18, 2008 10:50:43 AM
That is diesel-class thermal efficiency... assuming that it's measured net, not gross. 206 g/kWh is 0.34 lbm/hp-hr, which is fantastic.
We need these things rolled out tomorrow. Unfortunately, they're only the start of what we need.
Posted by: Engineer-Poet | May 18, 2008 11:55:18 AM
You could always put a big VGT turbo on this thing to compensate for the reduced specific power.
Or just put a normal turbo on it and run it as a gen-set in a PHEV.
Posted by: GreenPlease | May 18, 2008 3:59:12 PM
The specific power is far too low for a PHEV. At the efficiency peak, it's only generating ~23 kW out of a whopping 2 liters. The PHEV genset can operate at constant RPM and 100% load, so it is far better suited to an Atkinson cycle, perhaps with a turbocharger or Comprex pressure-wave supercharger to recover exhaust pulse energy also.
Posted by: Engineer-Poet | May 18, 2008 9:18:02 PM
This sounds like an updated version of using ceramic engines to boost thermal efficiency. Still would like to see the stats posted in real-world terms so we can make apples-to-apples comparisons. ie how much fuel is consumed at constant speeds all across the spectrum (this was common 40 years ago when Americans were paying thirty cents a gallon for gas) as opposed to phony epa figures
Posted by: ken | May 19, 2008 6:49:12 AM
Those figures would be specific to vehicles, not the engine per se.
Posted by: Reality Czech | May 19, 2008 9:34:07 AM
The real test data is right there verified independently in tabular form. This test was run for maximum brake fuel eff not power. that’s why you only see half power, any otto cycle ICE at full load with a fixed compression ratio and stoichiometric fueling which by definition sets the high load limit will have the same brake thermal efficiency. Its a simple matter of physics how much fuel at 14.7 to 1 AFR one can shove in a fixed volume at a fixed compression ratio, direct injection or port injection at full load both port injection and direct injection motors will be at 14.7 to 1 fuel loading and have the same brake fuel efficiency given both are now throttle less and both share the same compression ratio. what matters is that this engine can run at part load unthrottled that’s why you see almost diesel brake thermal efficiency because a diesel is throttle less from idle to full power. Once the throttle is removed only the geometric compression ratio determines brake thermal efficency of the otto or diesel combustion cycles. Besides most vehicles only need 25 kw or less to cruse at hwy speeds so going from 25% brake thermal eff. To 40+ % is a huge improvement. Add in a hybrid setup and use the electric motors to get up to speed while keeping the ice engine in the efficiency sweet spot. A hydraulic hybrid would be perfect for this application as hydraulic hybrids can accelerate large masses very rapidly to 40-50 mph and then let the ICE take over at its max efficiency.
Posted by: UT | May 19, 2008 11:51:40 AM
UT,
Maximum power will be no doubt restricted in comparison to a conventional GDI engine due to the presence of the orifice at the cylinder head that will restrict flow at high engine speed. This is not a high-power hotrod engine.
Furthermore, like Rafael has mentioned before, at leaner than stoichiometric combustion between lambda 1 to 3, there will be excessive NOx emission, above regulated limit, that will require diesel-type of NOx emission control that will be expensive...Unless cooled EGR technique is used in the Ricardo method for higher power lean setting that will be compatible with a 3-way cat...and a waste gate flow valve can be used to divert the exhaust away from the 3-way cat when MUSIC scheme is used at ultra-lean combustion regime.
The beauty of the MUSIC scheme is that cooled-EGR cannot be used at low power setting (unthrottled part-load) due to the impairment of flame propagation from excessive EGR. The marriage of both Cooled-EGR and MUSIC scheme will make a perfect high-efficiency unthrottled ICE.
Posted by: Roger Pham | May 19, 2008 12:16:02 PM
Gives to me , with the patent Roberta Krupy in the form {figure} FireStorm Spark Plug is the decidedly better less complicated to using in gasoline motors. MUSIC 20% fuel FireStorm Spark Plug 70% and to this 40 % height the engine power, 0 of emissions CO2 and this is science engine benzine-. Dear knows to the benzine one can pour some more H2O as spark produces plazme and in water not gasnie
Posted by: Henryk | May 19, 2008 1:50:01 PM
The MUSIC technology is explained in more detail on website www.musicombustion.co
Posted by: MUSIEngines | May 24, 2008 2:41:59 AM
