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Supercharged opposed piston engine with variable compression ratio

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Supercharged opposed piston engine with variable compression ratio is an advanced engine concept which uses the conventional mechanism in an innovative configuration.

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Supercharged opposed piston engine with variable compression ratio

  1. 1. 1 Supercharged Opposed Piston Engine – SOPE with Variable Compression Ratio Author: Liviu Giurca INTRO Few insiders of car manufacturers have proclaimed that battery-powered vehicles will account for 10 percent of global new-car sales by 2020. These producers introduced in the market at least six pure electric cars in the past years. Unfortunately, because of there limited autonomy these vehicles were not sold as expected initial. Independent analysts, however, believe that pure electric vehicles will remain at less than one percent of the new-car mix in 2020. A more likely spreading will be for hybrid or electric vehicles with extended range. Regrettably, the current price of these vehicles is prohibitive and because of this, can not be considered as being able to compete with the classic vehicles. The costs should be reduced by about 30% -40% considering the current market level. Reducing the costs can be made in two compulsory ways: producing a high number of units and reducing the component price. Referring to this second way, one of the main components of the hybrid vehicles or electric vehicles with extended autonomy remains the internal combustion engine. In actual configuration is expensive and inefficient. Also NVH levels are high, knowing that for the series hybrid vehicles and electric vehicle with extended-range the IC engine usually operates over 3000 RPM. On the other hand, even the internal combustion engines have been used for more than a century, significant improvements in energy efficiency and emissions reduction are still possible. Because of their relatively low cost, high performance, and ability to use renewable fuels (e.g. ethanol, CNG, biodiesel and hydrogen), conventional vehicles with combustion engines will likely dominate the market for at least the next 20 years. Globaly it is possible to cut the transportation fuel use with 20%–40% through commercialization of advanced engines. The new solution introduced by this presentation relates about a supercharged opposed piston having an alternative engine configuration with oscillating pistons, named Supercharged Opposite Piston Engine – SOPE, that attempts to correct certain deficiencies of the thermodynamic cycle as employed in conventional engines. The question is how the future solution will show? A radical engine concept will be difficult to be developed. It is necessary decades to validate a new concept even is very simple (e.g. Wankel engine). In contrast, if the engine presents the same mechanism with connecting rod, crankshaft, piston and rings, will be easily developed and also easily accepted by clients. For these reasons I choose this second way and the new concept is very similar with the conventional engine (four- stroke and two-stroke).
  2. 2. 2 STATE OF THE ART Historically, the opposed-piston engine set combined records for fuel efficiency and power density that have yet to be met by any other engine type. The fundamental thermal efficiency benefits of this engine type along with its low emissions, small package size and weight, and low cost relative to current engines make it an attractive alternative for future commercial and passenger vehicles. The precursor of this concept was the Junkers Jumo 207 Diesel Engine. Opposite piston Engine: Unmatched combination of Fuel Efficiency and Power Density [3] Some companies already developed concepts which present high power density. It is the case of the OPOC (opposed piston opposed cylinder) engine presented by Ecomotors with FEV. OPOC - Ecomotors
  3. 3. 3 It comprises two opposing cylinders per module, with a crankshaft between them, each cylinder having two pistons moving in opposite directions. This innovative design configuration eliminates the cylinder-head and valve-train components of conventional engines, offering an efficient and simple core engine structure. The result is an engine family that is lighter, more efficient and economical, with lower exhaust emissions. The big advantages of this concept are the power density which is around 2 kW/kg and the effective efficiency which is at least 37% in real proved conditions. The disadvantages are: -It is not adapted for automotive application, the external volume of the engine being developed into a single direction; -The scavenging of the cylinder is made by an external compressor, electrically acted, which present an important cost; -It is deigned as a single unit with two cylinders and to have more than that (4, 6 or 8) is very complicate; -Not four-stroke solution proposed. Another solution was proposed by me few years ago to achieve the simplest powerplant for hybrid vehicle: the two-stroke solid piston engine. The supercharged engine for hybrid application It is represented by a kind of “free piston engine” with crank mechanism. Having only three main parts in motion for each two opposed power cylinders it represents the simplest engine with reciprocating piston. Despite the simplicity, this arrangement contains two compressors included in the volume of the engine which supply with fresh air the combustion chambers. The advantages of this engine are the high power density, the simplicity of the concept, the lubrication similar with four stroke engine and the fact that the part of piston which works in the combustion chamber is suspended (it is no friction with the combustion chamber walls). Unfortunately the two cylinders engine works unbalanced. To have a balanced engine is possible only with two rows of cylinders (four cylinders) or more. SOPE DESCRIPTION This concept uses mostly the same elements as a conventional engine (four-stroke or two-stroke) configured in an innovative arrangement and shape.
  4. 4. 4 The four stroke variant has four valves per each cylinder has not cylinder had (fig. 1 and 2). Four-stroke engine The two pistons 8 and 9 act two crankshafts 13 and 11 synchronized by two gears 14 and 15. The two semi-cylinders are in shape of reverse V and the combustion chamber 23 is common for the two pistons 8 and 9. An intake camshaft 38 and an exhaust camshaft 42 act the four valves 29 and 32. The two semi-cylinders are displaced with a distance B to obtain the space for the valves 29 and 32. In this variant a turbocharger is used to supercharge the engine.
  5. 5. 5 In another four-stroke variant a mechanical supercharger is included in the volume of the engine (fig. 3). The supercharger 63 or 64 uses an extended oval portion of the piston 51 or 52 which can work in an oval cylinder 63 or 64. The piston looks like in figure 4. A two-stroke variant is also proposed (fig.5) which uses same piston type to obtain the air necessary for scavenging. In this case the semi-cylinders are aligned and are included in same engine block. The scavenging is of uniflow type.
  6. 6. 6 THE SIMPLEST VARIABLE COMPRESSION RATIO MECHANISM In general a variable compression ratio (VCR) engine is able to operate at different compression ratios, depending on the particular vehicle performance needs [1]. The VCR engine is optimized for the full range of driving conditions, such as acceleration, speed, and load. At low power levels, the VCR engine operates at high compression to capture fuel efficiency benefits, while at high power levels, it operates at low compression levels to prevent knock. In this case a very simple and reliable mechanism is used (fig. 7).
  7. 7. 7 The two gears 14 and 15 have inclined teeth. If they change the axial position one to another, the distance between the pistons at DTC can be varied. Consequently the combustion chamber volume at DTC and the compression ratio can be varied. An actuator 163 can act the gear 15 and in this time the other gear 14 has a fixed axial position. CONCEPT BENEFITS Making an analysis “Well to wheel” of the main propulsion systems with different paths, it can observe that the total efficiency of various SOPE engines (Diesel, SI- spark ignition are placed between the pure electric propulsion (if use only green energy) and the actual Diesel engine. The hydrogen SOPE is even more efficient than the fuel cell. For all SOPEs the CO2 emission is low and completely absent if it is used the hydrogen as fuel. Well to wheel analyzes
  8. 8. 8 A simple SOPE having same power is cheaper than actual engine even it can achieve a fuel economy and a CO2 reduction superior to 30%. The vehicle with SOPE range extender is more efficient than an actual hybrid electric vehicle and is not expensive. The client can recover the supplementary cost of around 1500 – 2000 $ in one or two years, which is not the case for the actual hybrid electric vehicle. Also in the utilization for electric vehicle with extended autonomy or for hybrid electric vehicles the proposed concept reduces the costs and leads to supplementary advantages as the reduced NVH level. The main advantages of this concept engine are: -Fully balanced mechanism and very good NVH behavior even with two pistons or four-stroke configuration ; -Having the compressor included in the volume of the engine it offers extreme power density of around 2.5 kW/kg; -Because is no cylinder head, the heat losses are diminished and the effective efficiency increase a lot, being around 45% for automotive application; This efficiency can be even bigger for stationary or medium speed marine engines; -The piston speed is diminished and the reliability of the engine is very much improved; -Easy to change the compression ratio and multi fuel capability; -The fuel injection system, the ignition system, the exhaust manifold and the intake manifold are simplified and that reduces drastically the costs; -Using extended expansion stroke can improve also the efficiency; -Comparing with OPOC engine 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 vehicle or for non electric hybrid;
  9. 9. 9 -It is very well adapted for the new fuels as CNG, LPG, biofuels and hydrogen doe to the possibility to include a compressor in the volume of the engine. For a middle class, gasoline car ( M=1300 kg, Cx= 0.30, S= 2.2 m²), the comparison with the calculated fuel consumptions between conventional and HOPE SI engines is described in the table 1. Table 1 Cycle Fuel cons. [l/100 km] Conventional SI CO2 [g/km] Conventional SI Fuel cons. [l/100 km] SOPE SI CO2 [g/km] SOPE SI Δ City 7.2 166 4.0 91.3 -45 % Inter-urban 4.6 106 2.5 58.3 -45 % Average 5.9 136 3.2 74.8 -45 % For a typical diesel truck, the comparison with the calculated fuel consumptions between conventional and HOPE diesel with heat recovery is described in the table 2. Table 2 Cycle Fuel cons. [l/100 km] Conventional Diesel CO2 [g/km] Conventional Diesel Fuel cons. [l/100 km] SOPE Diesel CO2 [g/km] SOPE Diesel Δ City 45 1035 24.7 570 -45 % Inter-urban 32 736 16 368 -50 % Both two-stroke and four-stroke engines are fully balanced even they use a single cylinder (and two pistons) and consequently this solution reduces a lot the noises and the vibrations. That means, even the engine is used at high RPM, the level of NVH will be low comparing with the actual engine without to use expensive parallel shafts (see the picture billow). “CONVENTIONAL Range extender” with balance shaft [2] The SOPE technology can be considered as “revolutionary” in terms of advantages and as “evolutionary” in terms of engine modifications (one crankshaft more).
  10. 10. 10 NEW RANGE EXTENDER WITH HOPE Making a comparison between a classic vehicle and a pure electric vehicle it can observe some big disadvantages of the electric vehicle such as the limited autonomy, the recharging time and the high cost. Adding a range extender to the electric vehicle (green color in the diagram) can obtain an improved autonomy, reduced charge time but also relatively low cost of the vehicle doe to the small battery package. That seems to be the best compromise to obtain the customer acceptance. After AVL [Assessment report on possible options for hybrid gas/electricity light-duty vehicles], there are several demands that have to be fulfilled by a range extender to be attractive on the market. The most important are listed below without prioritization. • Low system cost • Low weight • Small • Silent • Low vibration • Easy to integrate • Emission compliant (incl. CO2) • Legally compliant (crash, safety, EMC, noise, etc) • Availability of fuels The SOPE concept, in the configuration for hybrid vehicle or for electric vehicle with extended range, can have an ultra-compact structure even in association with a starter-alternator. This auxiliary unit, having high power density, is very simple and cheap because the engine is simple and cheap. The total weight can be very low and consequently this power unit can be transported by people and moved from the vehicle when is not need it. This represents the concept of the portable range extender.
  11. 11. 11 A 30 kW power unit (having a starter-alternator) designed for hybrid or for electric vehicle with extended range can have a weight of around 24 kg. The engine is fully balanced even with only two pistons and consequently the NVH level is reduced including to high RPM. The proposed concept satisfies completely the requirements for a range extender. FURTHER DEVELOPMENT: SOPE WITH HEAT RECOVERY The most important evolution of SOPE is the recovery of both exhaust gas heat and cooling heat. Modern late 21th century power plants, utilizing combined heat and power, could yield an overall efficiency as high as 60%, where different working fluids drive different power driving cycles, obtaining a combined thermal efficiency. For an advanced SOPE with heat recovery, the produced energy and the recovered energies are collected as power directly by the engine shaft and all the process is developed in an ultra-compact and simple structure. The estimated SE global efficiency No. SOPE Variant SI CI 1 With Exhaust gas heat recovery 50 % – 55% 60 % – 65% 2 With Exhaust gas heat recovery + Cooling system heat recovery 60 % – 65% 70 % – 75%
  12. 12. 12 PATENT PROTECTION Multiple patent applications were registered. One of them is already published by the Patent Office. The patenting process is ongoing. BIBLIOGRAPHY 1. OAAT ACOMPLISHEMENT, New engine design adjusts compression to meet driving conditions, http://www1.eere.energy.gov/vehiclesandfuels/pdfs/success/vcr3_29_01.pdf 2. SETC2011- JSAE 20119595 / SAE 2011-32-0595, Compact Engine Architecture for Best Fuel Efficiency and High, Performance – Challenge or Contradiction, Christian Hubmann, Wolfgang Schöffmann, Hubert Friedl, Michael Howlett AVL List GmbH] 3. http://en.wikipedia.org/wiki/File:Opposite_piston_engine_anim.gif Animated sectional view of an opposite piston engine / Animierte Schnittansicht eines Gegenkolbenmotors Source: self-made UtzOnBike with Autodesk Inventor {{GFDL}} Category:GFDL Contact info: lgiurca@hybrid-engine-hope.com WEB site: www.hybrid-engine-hope.com Phone: 0040731015778

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