Hybrid Opposed Piston Engine HOPE

Author: Eng. Liviu Giurca

Hybrid Opposed Piston EngineHOPE

Liviu Giurca01 Oct. 2013

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Introduction

The new solution introduced by this engine concept describes an alternative configuration with toroidal oscillating

pistons, named ’Hybrid Opposite Piston Engine’ or HOPE, which attempts to correct certain deficiencies of the

thermodynamic cycle as employed in conventional engines.

Why is this engine called a “hybrid”?

•It has the potential of achieving in itself the full exhaust gas

energy recovery as well as the engine brake power recuperation;

•It can work as a four-stroke or as a two-stroke engine;

•It can be used for all means of transportation as well as for

stationary power units.


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State-of-the-Art Opposed Piston Engines

OPOC (opposed piston opposed cylinder) - by Ecomotors

Limitations:

- Not adapted for automotive application due to external volume of the engine being developed into a single direction;

- Scavenging of the cylinder is made by an electrical external compressor;

- Designed as a single unit with two cylinders; it becomes very complicated to have more than that (4, 6 or 8 cylinder units);

- A four-stroke solution has not been proposed yet.

Achates Power Diesel Engine

Limitations:

- Scavenging of the cylinder is made by an electrical external compressor.

- It has a complex construction.

- A four-stroke solution has not been proposed yet.


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State-of-the-Art Opposed Piston Engines

Niama-Reisser Engine

Limitations:

- High thermal stress;

- Scavenging of the cylinders is made by an electrical external compressor.

-Uses an ‘exotic’ slide mechanism with unproven durability.

Huettlin engine

Limitations:

- Uses a cam mechanism to transform the oscillating motion in rotation motion which limits the maximum engine speed at 3000 RPM;

-The piston stroke is relatively short (an extended expansion stroke is not tolerable);

- A configuration with more than two cylinders becomes extremely difficult;

- Relatively low power density.


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Fundamental Limitations on Classic Engines

•The commonly used four-stroke and two-stroke engines have a number of fundamental

disadvantages:

•Complicated and expensive construction due to requirement for the cylinder head;

•The cylinder head diminishes significantly the engine thermal efficiency through heat losses;

•The piston stroke is limited due to packaging constraint causing an important exhaust gas

energy loss;

•The piston-cylinder side force increases the engine internal friction causing wear;

•Displacement downsizing is made with difficulty increasing the overall engine cost;

•The variable compression ratio (VCR) is a complex task being an expensive feature;

•In any configuration with less than four cylinders the NVH level remains high.


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Description of HOPE Concept

HOPE concept - version with double crankshaft mechanism:1. toroidal cylinder2. toroidal pistons3. piston crown where the rings are mounted on4. rocker arms5. central joint located in the torus center6. ball-joint7. connecting rod8. crankshaft9. gears (1:1 ratio)10. combustion chamberA physical model of this mechanism was successfully tested:

http://www.youtube.com/watch?v=TsmJbew0adA


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HOPE concept - version with single crankshaft mechanism:

1. toroidal cylinder

2. toroidal pistons

3. piston crown where the rings are mounted

4. central joint located in the torus center

5. Crankshaft

6. rocker arm

7. connecting rod


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Two-Stroke EngineDouble Crankshaft

Four-Stroke EngineSingle Crankshaft


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HOPE Construction Characteristics

•The following characteristics are applicable to both HOPE two and four stroke cycle versions:

•Reduced weight and number of components due to:

No cylinder head _ two-stroke or a simplified cylinder head _ four-stroke;

single toroidal cylinder for two pistons;

single injector for two pistons;

•No friction between pistons and cylinder (each piston works suspended in the rocker arm);

•Fully balanced mechanism even with two pistons;

•Uniflow scavenging process;

•Variable compression ratio easily achievable by changing the relative position between one crankshaft

and its corresponding gear;


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HOPE Combustion Characteristics

The fuel supply and the ignition systems are similar as for the classic engines. However, the combustion

process in HOPE has specific characteristics as follows:

•An extended expansion stroke (1.5-3 stroke/bore ratio) offers the best use of heat with the gases reaching

close to atmospheric pressure before the exhaust port is open;

•A reduced heat loss due to lack of or a reduced cylinder head (totally for two-stroke and simplified for four-

stroke) allowing up to 50% reduction of the surface-to-volume ratio compared to a conventional engine of

equal displacement;

•The version with two crankshafts permits a variable compression ratio beside other benefits making it

suitable for different types of fuels with minimal adaptations.


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Simplified p-V diagram

Simplified p-V thermodynamic cycle diagram of HOPE concept with extended expansion stroke which allows for complete use of exhaust gas energy

The extended expansion stroke is obtained by choosing a large supra-unitary piston stroke-bore ratio (1.8 to 3) without a significant increase of the size and weight of the engine assembly


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Hybridization

There are three proposed applications for HOPE as part of a hybrid system:

1.Pneumatic Hybrid Engine

2.Power Generator on a Hybrid Electric Vehicle

3.Portable Range Extender for Electric Vehicles.


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1. Pneumatic Hybrid Engine

The Pneumatic HOPE concept is made using a mechanical control between the existent exhaust air circuit connected to the combustion chamber and an air tank. In engine braking phase with fuel in cut-off mode, the engine pumps the intake air into a high pressure tank. The pressurized air can later be used as a bonus to supercharge the engine.Compared to some existing vehicle electric hybrid systems, the proposed solution eliminates the electric generator/motor assist and battery components which are additional to the engine.This type of application reduces cost, complexity, and weight while providing similar function and benefits. Air, even when compressed to high pressure, remains very light, and therefore the added weight is, essentially, limited to the weight of the tank. Consequently, this small weight increase of the proposed hybrid system does not penalize the base vehicle fuel economy.


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2. Power Generator on a Hybrid Electric Vehicle

At the end of the present decade likely 30% of the global vehicle production will be composed from hybrid electric vehicles or electric vehicles with extended autonomy. These need a power range from 30 to 130 kW from IC engines. This power range can be obtained with the HOPE configuration only with two pistons and one cylinder. Even in this configuration, the engine is fully balanced and has low NVH at high RPM level without additional balancer shafts. The HOPE concept can have an ultra-compact structure even in association with a starter-alternator. A 30 kW power unit (including a starter-alternator) has a weight of approximately 24 kg.


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3. Portable Range Extender for Electric Vehicles

Having HOPE as a removable or portable range extender engine for an electric vehicle with the great advantage of being able to be shared within a fleet of electric vehicles.The engine will have quick-connect points for all the necessary auxiliary sytems (fuel, electrical, cooling, and exhaust systems) when mounted on the electric vehicle at the times when the driver needs an extended range such as interurban trips.This brings down the cost of a single portable engine which is shared within a fleet of electric vehicles which otherwise do not need to have a range more than the daily average commute (50 – 60 km). This reflects as well in the price of the electric vehicle.HOPE qualifies for this option as it has a very light construction with a great power density, being easily moved around by people from one vehicle to another or put into storage when it is not need it.


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Manufacturing Considerations

•There are no special challenges to manufacture the HOPE engine.

•An Argentian company named Tausem already produces in series a pendulum toroidal compressor. This demonstrates that the technology to achieve well finished toroidal cylinders is existent and applied in mass production.

Tausem Toroidal Compressorhttp://www.tausem.com.ar/interior_espanol.html

All the other components of HOPE are similar or identical with those used in the conventional engine.


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Production Cost Estimate

•A one-cylinder HOPE engine unit can replace a three or four-cylinder conventional engine (in the range of 30-130 kW).

Also the cylinder head is missing or simplified which reduces drastically the production cost and makes this new concept

attractive for engine manufacturers. For the same power level HOPE is with 30% cheaper than a conventional engine.


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Well-to-Wheel Efficiency Analysis

Based on a “Well-to-Wheel” analysis of

the main propulsion systems with

different paths, it can be noted that the

overall efficiency of various HOPE

engines (Diesel, SI- spark ignition and

PHE – pneumatic hybrid engine) is

placed between the pure electric

propulsion (when only uses renewable

energy) and the actual Diesel engine.

The hydrogen HOPE with exhaust gas

recovery achieved as a pneumatic

hybrid engine (PHE) is even more

efficient than the fuel cell. For all HOPE

versions, the CO2 emission is low and

completely absent when uses hydrogen

fuel.


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HOPE Main Advantages

•Fully balanced mechanism with very good NVH behavior even with only two pistons in a four-stroke configuration;•The pistons glide inside without touching the cylinder wall, a fact which diminishes the overall internal engine friction with about 20% and increasing substantially the efficiency and the piston-cylinder reliability;•Because doesn’t have a cylinder head, the heat losses are diminished and the effective efficiency increases a lot, being close to 50% for an automotive application; this efficiency can be greater for stationary or medium speed marine engines;•The fuel injection system, the ignition system, the exhaust manifold and the intake manifold are simplified and that reduces drastically the costs;•The combustion takes place at constant volume (geometrically) minimizing again the heat loses and the incomplete burn rate;•Using extended expansion stroke can improve also the efficiency;•Having the compressor included in the volume of the engine, it offers extreme power density at around 2.5 kW/kg;•Easy to change the compression ratio in the configuration with two crankshafts, respectively modifying the relative position between the one gear and its associated crank;•Comparing it with OPOC engine or Achates Power engine, HOPE is more compact, being very well adapted for automotive applications;•It represents a real world solution for the portable range extender used by the electric vehicle with extended autonomy, for low cost hybrid electric vehicles or for non electric hybrid vehicles.•It is very well adapted for the alternative fuels such as CNG, LPG, biofuels and hydrogen due to the possibility to include a compressor in the volume of the engine.


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Conclusion

The HOPE engine concept described in this presentation can be used as prime mover for terrestrial, marine or

aerial vehicles as well as for the stationary applications. By the end of the current decade, likely 30% of the

global vehicle production will be composed from hybrid vehicles which can use HOPE. HOPE engines operate

successfully as hybrid engines integrated within the powertrain of the hybrid electric vehicles or in the electric

vehicles with extended autonomy. Because it is simpler, more efficient and much cheaper (approx. by 30%)

than the conventional engines with the same level of power and emissions, HOPE is able to replace the

contemporary engine technology.

•Contact info:

•[email protected]

•URL: www.hybrid-engine-hope.com


Author’s details

Liviu Grigorian Giurca is an automotive engineer which accumulated experience working for international companies as Ford, Renault, Daewoo Motors, IDEA Institute , AKKA Technologies or MSX International. He has a 7 patented inventions. He also contributed in many innovative projects as Renault/Dacia Logan, Sandero and Duster (the most innovative projects in terms of cost reduction) or Ford EcoBoost 1 L engine awarded as the Engine of the Year in 2012 and 2013.

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Hybrid Opposed Piston Engine HOPE