Lotus has just got an animated website to explain how Lotus omnivore engine works which utilise multi fuel gasoline and alcohol as source of power by using variable compression ratio VCR system which gives up to 15% fuel saving than normal engine in any condition. This is a very unique technology and a very smart fuel effiecient and environmental friendly. We will help you to understand further about the Lotus omnivore engine below. For fun testing, you can go to www.grouplotus.com/manageshowcase/uploadpassthru/8628.swf
According to Lotus, compared to gasoline, alcohol fuels have a higher knock resistance and therefore need to run at higher compression ratios to maximize thermal efficiency. The option to run alcohol fuels in conventional fixed compression multi fuel engines requires a compromise of thermal efficiency to allow for gasoline operation. The VCR mechanism of OMNIVORE allows any variation of fuel combinations to be used at maximum thermal efficiency without any hardware change to the engine.
LOTUS OMNIVORE ENGINE – MULTI FUEL VARIABLE COMPRESSION RATIO FUEL SAVING CONCEPT
The engine has so far been run on gasoline and in both spark ignition and homogeneous charge compression ignition (HCCI) modes. The HCCI mode is of particular interest because it is capable of providing diesel engine-like efficiency without the particulate and NOx emissions that require expensive after-treatment systems in a standard diesel engine. Lotus is claiming the Omnivore can operate in HCCI mode in a wide variety of operating conditions and even from a cold start, something that has been problematic for previous HCCI engines. According to the initial test results, the Omnivore is achieving up to a 10 percent improvement in efficiency (as measured by Indicated Specific Fuel Consumption) compared to existing spark ignition direct injected engines.
The Lotus Omnivore engine uses a variable compression ratio system with a 2-stroke operating cycle and direct injection. The Lotus Omnivore engine has been developed for flex-fuel operation and offers better optimization than the four stroke engines.
Lotus Engineering, the world-renowned automotive consultancy division of Lotus Cars Limited, unveils its latest research into engine efficiency at the 79th International Geneva Motor Show. The Omnivore engine concept has the potential to significantly increase fuel efficiency for sustainable alcohol based fuels, which increases the prospect of a greater amount of vehicle miles traveled using renewable fuels. On display will be the single cylinder research engine monoblock that
demonstrates the novel architecture designed for high thermal efficiency when fuelled on any alcohol based fuel or gasoline.
The Omnivore concept features an innovative variable compression ratio system and uses a two-stroke operating cycle with direct fuel injection. It is ideally suited to flex-fuel operation with a higher degree of optimization than is possible with existing four stroke engines.
The engine concept features a monoblock construction that blends the cylinder head and block together eliminating the need for a cylinder head gasket, improving durability and reducing weight. In this case, the application of a monoblock is facilitated by the absence of the requirement for poppet valves. A novel charge trapping valve in the exhaust port allows asymmetric timing of exhaust flow and continuous variation of the exhaust opening point.
The variable compression ratio is achieved by the use of a puck at the top of the combustion chamber. This simple, yet effective system moves up and down affecting the change in geometric compression depending on the load demands on the engine.
The monoblock incorporates the cylinder head, the cylinder barrel and the inlet ports, together with mounts for the variable compression ratio system and the charge trapping valve housing. It also contains the non-moving location of one of the two possible injector mounting positions provided for research purposes. The other injector position is in the variable compression ratio puck.
The monoblock is mounted on the upper crankcase, which is a common component with all of Lotus’ single-cylinder research engines. The engine carries a full primary and secondary balancer system. The monoblock is watercooled by an electric water pump. Computational fluid dynamics is used extensively to ensure effective cooling of the monoblock, a feature assisted by the removal of the cylinder head gasket, inherent in such architecture. The chief advantage of a monoblock construction in any engine, aside from the bill of materials and assembly benefits, is the reduction of bore distortion afforded by the removal of cylinder head bolts. This is especially important in piston-ported 2-stroke engines.
LOTUS OMNIVORE ENGINE - MULTI FUEL VARIABLE COMPRESSION RATIO FUEL SAVING CONCEPT
Variable Compression Ratio Mechanism
The primary component of the variable compression ratio mechanism is what is termed the ‘puck’, or a moveable junk piston in the cylinder head. In the
case of the research engine, this puck is driven in and out by a doubleeccentric mechanism itself comprising proprietary parts. The puck itself does not move at engine speed. In addition to the spark plug, the puck carries one
of two possible injector positions. It is water-cooled and carries simple piston (or ‘junk’) rings for primary dealing, and an ‘O’-ring towards the top for final
sealing. The variable compression ratio system is controlled by an electric motor and worm drive arrangement at the front of the engine. Because there are no poppet valves in the engine, it is clear that the puck could be of a large diameter and since there is no need for valve cut-outs in the piston crown, the minimum volume of the combustion chamber can be much smaller than has been the case in variable compression ratio engines shown to date. When the puck is in its innermost position, its surface is essentially coincident with that of the combustion chamber squish band and this yields the highest compression
ratio of 40:1. The combustion chamber geometry necessarily alters as the puck is moved to vary the compression ratio. The chamber geometry in Omnivore was therefore chosen on the basis of 2-stroke experience in spark ignition operation. Consequently, the puck is positioned in the cylinder head in such a way that the non-moving squish band directs cooling flow towards the spark plug. The puck is water-cooled from the main engine cooling circuit.
Configuration : Single-cylinder loop-scavenged 2-stroke
Operating cycle : Modified two-port two-stroke cycle
Combustion system : Homogeneous charge compression ignition
Bore x Stroke : 86 mm x 86 mm
Displacement : 499.6 cc
Compression ratio : 10:1-40:1
Porting arrangement : Schnürle loop scavenging with five transfer ports and one exhaust port fitted with Lotus charge trapping valve providing asymmetric and continuously-variable exhaust port timing
Ring pack : Two pegged half-keystone compression rings in upper section, unpegged Napier and U-Flex oil control rings in lower section for oil control and containment
Fuel system : Orbital FlexDI air-assist
Scavenging air supply :Via external rig; adjustable flow
Lubrication system : Wet sump with plain bearings and electric oil pump
Cooling system : Electric water pump
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