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Ricardo and Partners Complete 2/4SIGHT Prototype Program; Projected 27% Fuel Savings

25 March 2008

24sight
The 2/4SIGHT engine enables automatic switching between two- and four-stroke mode. Click to enlarge.

Ricardo and a consortium of automotive partners have completed an advanced prototype research program based on the 2/4SIGHT engine concept. (Earlier post.) This gasoline engine concept uses novel combustion, boosting, control and valve actuation technologies to enable automatic and seamless switching between two- and four-stroke operation, with the aim of delivering significant performance and fuel economy improvements through aggressive downsizing.

Simulation results based on a 2.0-liter 2/4SIGHT engine indicate a 27% reduction in fuel consumption while maintaining comparable acceleration performance compared to a naturally aspirated 3.5-liter engine.

24sight2
The 2/4SIGHT prototype on test. Click to enlarge.

The 2/4SIGHT engine concept uses a direct injection gasoline combustion system in which the design of intake and exhaust ports, combined with appropriate changes in boost supply, fuel injection, ignition and valve timing, enable operation both in two-stroke and four-stroke modes. An advanced control system coupled with flexible valve actuation manages driver demands and coordinates operation of the boost system, valves and fuel injection equipment at an individual cylinder level.

A dedicated Valve Control Unit (VCU) controls each hydraulic valve; therefore, each cylinder can be independently controlled in all the operating conditions (2 stroke, 4 stroke and transitions). This enables smooth transitions between two- and four-stroke operation without torque interruption in both transient and constant torque conditions.

The research prototype engine is based on a single bank of a 2.1-liter V6, which in 6 cylinder 2/4SIGHT configuration is intended to deliver levels of performance and driveability more usually associated with a 3- to 4- liter V8 gasoline engine.

In order to enable the project team to assess control strategies in a completely unrestricted manner, an electro-hydraulic valve (EHV) actuation system was used for the prototype development rig. The air handling system of the 2/4SIGHT concept is based on two-stage boosting and intercooling using a Rotrex supercharger and Honeywell turbocharger. For simplicity in the initial test bed prototype configuration however, boosting is provided by an external compressed air supply. The engine control system of the prototype is a DENSO rapid prototyping system working with DENSO gasoline direct injection and ignition components. The prototype engine was built at the Ricardo Shoreham Technical Centre and installed for testing at the Sir Harry Ricardo Laboratories of the University of Brighton.

Testing of the prototype 2/4SIGHT engine has enabled development and validation of the combustion system which has been optimized for operation in both two and four-stroke modes. The flexibility of the advanced control system—developed jointly by DENSO and Ricardo—allows rapid changes to high level code which, coupled with the flexibility of the EHV valvetrain, has enabled the project team to develop and optimize a new control strategy for the 2/4SIGHT engine, including the management of two-four-stroke switching.

Highlights of the development test results include:

  • Smooth and reliable switching between two- and four-stroke modes under both constant torque conditions and transient operation.

  • Control strategies amenable to implementation in cost-effective mechanical valvetrain hardware.

  • Extremely high two-stroke specific torque demonstrated of 150 Nm/L at 1,000 rev/min and 230 Nm/L at 2500 rev/min, opening the prospect of highly aggressive engine downsizing using the 2/4SIGHT engine concept.

Following completion of the test program, Ricardo carried out a vehicle drive cycle and acceleration performance simulation based on the steady state fuel consumption and full load performance of the 2/4SIGHT engine. The study was carried out using the Ricardo powertrain blockset in the MSC EASY5 software package that allows detailed modelling of engines, transmissions, drivelines, tires and aerodynamics.

The baseline vehicle for the study was an 1,800 kg passenger car sold in the European market with a 3.5- liter naturally aspirated V6 gasoline engine and 5 speed conventional automatic transmission with torque converter. To verify the validity of the models and input data, the baseline vehicle fuel consumption results were compared with published data, which were reproduced by the model to an acceptable accuracy of 1%.

The simulation results indicate that vehicle acceleration performance, including launch from rest, can be maintained with a 2.0-liter V6 2/4SIGHT gasoline engine replacing the 3.5-liter baseline powerplant. This would deliver fuel savings of 27% over the New European Drive Cycle (NEDC) and would reduce the vehicle CO2 emissions of the baseline from 260 g/km to 190 g/km.

In parallel with the prototype engine development effort in the UK, Ricardo engineers at the company’s Detroit Technology Campus have designed a patented mechanical cam switching system which is capable of delivering the required switching performance for the control strategies developed on the test bed using the EHV system for the 2/4SIGHT engine. This not only opens the way for packaging and integration of the 2/4SIGHT engine into a production vehicle but also represents a highly cost-effective means of implementation of this efficient combustion concept. A future gasoline engine equipped with 2/4SIGHT technology offers the prospect of superior performance and lower production cost than other advanced gasoline and diesel powertrains, and straightforward compliance with gasoline engine emissions standards.

Having completed development of the prototype 2/4SIGHT engine, the partners are currently negotiating potential sources of funding and support for a vehicle demonstration program.

The 2/4SIGHT project was led and coordinated by Ricardo, which was also responsible for design and development of the prototype engine and integration of its systems. DENSO was responsible for development and supply of the direct fuel injection and advanced engine control systems. Ma 2T4 contributed its knowledge and expertise of valvetrain switching technology. Brunel University carried out single-cylinder engine testing and development. The University of Brighton carried out multi-cylinder engine testing and combustion and cooling system analysis. The 2/4SIGHT project was part-funded by the British Government through the Technology Strategy Board.

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March 25, 2008 in Engines, Fuel Efficiency | Permalink | Comments (24) | TrackBack (0)

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Comments

The two cycle engine is notorious for producing pollution.

So far, I don't see this being addressed. Sure a smaller four-stroke will be better on fuel economy and therefore on overall emissions, but the hefty pollution price paid during two-stroke acceleration is dad news.

Will this take cars back to the old "blue-smoker" days?

This could also be used to downsize a diesel, cutting engine weight and friction losses.  If a similar cut in fuel consumption was achieved by going from e.g. 2.0 liters to 1.2 liters displacement, my Passat TDI could achieve better than 50 MPG highway with no compromise in performance.

John:  You're thinking of 2-cycle engines which breathe through the crankcase and are lubricated by oil mixed with the fuel.  This engine is nothing like that.

Jon

A 2 stroke engine can be as clean as a 4 stroke as it has already been demonstrated by orbital. The main problem is the breathing. Still I don't really see the necessity to swith from 2 to 4 stroke, you can use cylinder deactivation or jump one firing out of two with the same results. The interest of 2 stroke is obvious in hard downsizing without a turbo. The other problem of 2 stroke is that it is not compatible with an atkison cycle (well the turbo as well)

A piston-ported 2-stroke isn't compatible with the Atkinson cycle, but this engine has hydraulic poppet valves.  It would appear simple to control cylinder air charge by varying the delay on intake-valve closure, though this might create difficulties with turbocharger surging unless the turbo also had a waste gate.

An engine which performs much of its compression with a turbocharger and requires no throttle under most load conditions would be highly efficient.

Treehugger

If the 2 stroke part could move a silverado/f150/dodge ram 1/2 ton pickup off the line like a v8 with a 2l diesel and get >30mpg overall I think the American car companies might sell a few.

John: You're thinking of 2-cycle engines which breathe through the crankcase and are lubricated by oil mixed with the fuel. This engine is nothing like that.

And due to direct injection fresh fuel cannot escape through the exhaust before combustion, because the exhaust valve will be closed when fuel is injected.

Also in a 2-cycle engine without valves the intake and exhaust timing is symmetrical and exhaust port always closes after intake port.

@ John Taylor -

there are many more types of two-stroke engines than there are of four-stroke engines.

In two-stroke mode, this particular design uses head scavenging, which generally considered suboptimal but unavoidable in an engine that can also run as a four-stroke. The big advantage compared to the better-known crankcase scavenging is that there is a wet sump and no exhaust port that the piston rings need to slide past, ergo no blue smoke and no coking problems.

Given that discrete cam profile switching has been around for a long time (cp. Honda V-Tec, Porsche Variocam and others), the focus of development here was probably on the precise geometry of the cylinder head and valve masks, to achieve an optimal compromise between the two modes.

@ Engineer-Poet -

in two-stroke mode, valves are typically open for roughly 120 degrees crankshaft with a 30 degree phase shift. A turbo will deliver scavenging air but not as much boost pressure as in the case of a four stroke, so power is not doubled. Just as well, with twice as many combustion events, cooling is even more critical anyhow. Two-stroke diesels tend to run at low RPM (marine & locomotive applications), in part to allow for more complete combustion and additional cooling.

Ricardo's design is apparently a gasoline engine, which raises the issue of how they meet NOx emissions in two-stroke mode. Even if the air-fuel mixture is slightly rich to compensate for the extra oxygen in the scavenging air, it's hard to keep the equivalence ratio within 0.02 of unity. Three-way catalytic converters do have limited oxygen adsorption capability, but tellingly, the article does not discuss toxic emissions.

If this engine was only driven in 2 cycle mode it could make a nice engine for a series/plug-in hybrid.

(more power less weight and less volume).

It is amazing to see how $4+/gal fuel can provoke improved design. Imaging what $10+/gal would do.

Engines and vehicle weight can certainly be downsized by 50%+. Compounded downsizing + lower drag design + low resistance tyres + 7-speed transmission or CVT etc can certainly produce a 50 to 60 mpg reasonable size car.

The same technology improvements could produce a 100 mpg hybrid. Toyota is aiming at a 93 mpg hybrid in the near future.

I have the same concern as Rafael regarding practical emission control of NOx and excessive heat problem.

Direct-injection and turbocharged 4-stroke engines today are already very powerful, having 100 hp/liter specific power rating. Specific output is more limited by heat rejection and engine durability rather than any other factors. I don't see how much a 2-stroke mode will add to improve power output when heat and durability are still the limiting factors in engine downsizing.

It is possible to run this engine using gasoline stoichiometrically in 2-stroke mode if the exhaust valve is closed right after blowdown, before the intake valve will be opened any significant length of time, hence, no escape of free air (O2), but there still the heat problem to be dealt with due to the very high EGR (Exhaust gas recirculation) ratio, as the exhaust gas remaining in the cylinder will be very hot, forcing late injection of gasoline at near TDC to prevent pre-ignition, and then we will have to deal with higher PM emission, and maybe high NOx also (?), due to the residual heat in the EGR, and higher cost of high-pressure gasoline direct injection system, and the higher cost of electro-hydraulic valve system. A blower is still needed to force air into the cylinder in the 2-stroke mode, so no saving there, either.

I still think electric-ICE hybridization offers the most practical, efficient and cost-effective engine downsizing of any other options for engine downsizing.

@ Roger -

normally, two-stroke engines always feature substantial negative valve overlap, precisely because EGR levels would otherwise be very high. That would cause heat problems and possibly, engine knock.

However, this engine has two tricks up its sleeve. First, direct injection, which cools the compressed gas a little by evaporation. Second, Ricardo have given it the option of switching to HCCI combustion. Japanese researchers actually first observed that in two-stroke engines way back in 1979. Two-stroke HCCI gensets are stable at constant speed and load, but combustion control during rapid transients has so far only been achieved with four-stroke engines.

My 1972 Kawasaki H2 750cc 3cyl 2-stroke went into HCCI mode accidentally once. It was weird, I pulled out the key and it would not shut off.

Im not sure why all the fuss about the 2s mode. It is just used during WOT to get the peak power up and the time spent there is low. 90% of the time will be spent in 4s mode.

The power density increase (to ~ 125/150 hp/l)and resulting base engine size reduction will be a huge improvement.

Emissions should really be no different than the 4s as the engine will most likely be operated at the same AFR (12.5 or so) at WOT.

Also, it will be interesting to see this with diesel.

Very cool stuff

I don't see how much a 2-stroke mode will add to improve power output when heat and durability are still the limiting factors in engine downsizing.

At least one advantage of the 2-cycle over 4-cycle is, that the BMEP can be lower at the same power output. This means maximum forces on piston, rods and crankshaft are also lower at the same power output - which again means a reduction in engine weight.

A "comprex" pressure wave compressor would be nice.
About stationnary engines, why not build high Nox engines as micro fertiliser plants ? A catalyser may be fitted inside the combustion chamber. The exhaust gases must be water scrubbed, and the effluent used as a nitogen fertiliser (weak nitic acid solution). N fertliser is getting expensive as Haber-Bosch plants run out of cheap natural gas.

A turbo will deliver scavenging air but not as much boost pressure as in the case of a four stroke, so power is not doubled.
Which was obvious from the article (roughly 1.75x increase).

The advantage of doing this with a diesel is that the internal EGR and blown-through air don't matter nearly as much, and the reduction in size (and probably cylinder count) would cut both weight and cost; going from 4 injectors to 3 cuts 25% of that costly section.  If you could get reasonable acceleration and even towing performance in a full-size minivan with a 1.5 liter engine, the savings in fuel could be dramatic.

@Philippe

I like where your head is at. Perhaps farm equipment could be designed to have high NOx output which could be scrubbed with water and then immediately used on the soil.

This should result in better fuel efficiency, lower cost engines (no NOx after treatment), and a reduced need for CH4 based fertilizers.

globi stated:

"At least one advantage of the 2-cycle over 4-cycle is, that the BMEP can be lower at the same power output. This means maximum forces on piston, rods and crankshaft are also lower at the same power output - which again means a reduction in engine weight."

In theory, you are quite correct, for piston-ported 2-stroke with large intake port...However, poppet-valved 2-stroke is much more restricted in airflow at high speed, such that it takes as much as 180-230 degrees of exhaust valve opening for adequate expulsion of exhaust gas at high speed...in the two-stroke mode, you have about 90 degrees of crank angle for exhaust gas expulsion, meaning that instead of developing maximum power at 6000 rpm, a two-stroke poppet valved engine can only do 3000 rpm at maximum power. The BMEP and maximum power output will still be the same, or comparable, only that you'll need 6,000 rpm in the 4-stroke for 3,000 power strokes, vs. 3000 rpm in a 2-stroke. Slightly less efficiency in the 4-stroke due to higher engine friction, but much cheaper valve train and lower-pressure injectors than this Ricardo setup here.


to fix italic problem.

I'm for this if it can produce >160hp/liter. 177-180hp/liter seems to be the max for the production vehicles at this point. Assuming the 27% efficiency gains are from downsizing and DI vs a larger NA with PI, its no better than a new Mitsubishi Lancer Evolution X GSR FQ-360. Mahle has a great downsized turbo gasoline engine concept, though with a less extreme 163hp/liter.

As for NOx and PM concerns, a hydrogen supplementation system, like one from Hy-Drive (albeit smaller and lighter), may do the trick. Replacing the Lead acid battery with a NiMH or Li-ion, and a small motor/generator connected to the powertrain would provide the necessary electrical energy via regenerative braking. One may even add an onboard water distillation systems utilizing waste heat.

@Philippe

I like where your head is at. Perhaps farm equipment could be designed to have high NOx output which could be scrubbed with water and then immediately used on the soil.

This should result in better fuel efficiency, lower cost engines (no NOx after treatment), and a reduced need for CH4 based fertilizers.

The baseline vehicle for the study was an 1800 kg passenger car sold in the European market with a 3.5 litre naturally aspirated V6 gasoline engine and 5 speed conventional automatic transmission with torque converter. In other words your basic gas guzzler I suppose.
The simulation results indicate that vehicle acceleration performance, including launch from rest, can be maintained with a 2.0 litre V6 2/4SIGHT gasoline engine replacing the 3.5 litre baseline powerplant.

I hate to rain on anyone's parade here, my studies on gasoline engines have revealed that if you halve the stroke of any engine. Then, providing the new bore/ stroke ratio doesn't exceed 1.5 which usually it does not, then you can run the new engine at twice the rpm, but getting only half the torque of course. You will be back where you started with the exact same power but doing it with only half the literage. Thus I debunk the old saying "There's No Replacement For Displacement" And since the stroke is being reduced by only 50mm, in this case, it doesn't save much weight in an engine that may be around 500mm tall. Bottom line - a 2.0L V6 saves almost nothing over a 3.5L V6 since both of these powerful engines could be just idling, at the same rpm, while propelling the vehicle at a nominal road speed of 65mph.

In case you are wondering what they might have done instead. Just a minute while I drop the tone arm on the record. " The suggestion is that one way to downsize is to simply reduce the number of cylinders but be sure to maintain the same TOTAL piston area as before by enlarging piston diameters. You can prevent the bore/stroke ratio from exceeding 1.5 by increasing the stroke to suit. Finally top rpm speed for the engine will be when the MEAN piston speed approaches 20m/sec (4000fpm). This rpm, of course, is dependent on the stroke length you chose earlier.

This suggestion comes from the result of examining 50 engines from different manufacturers scrutinizing their output figures against their dimensions to discover correlations. Correlation was found in close agreement when considering naturally aspirated fuel injected engines."
T2

"If this engine was only driven in 2 cycle mode it could make a nice engine for a series/plug-in hybrid."

"Two-stroke HCCI gensets are stable at constant speed and load..."

It seems that if the series hybrid approach becomes popular, then the choice for the ICE in the engine/generator set gets more interesting.

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