Quote:
Originally Posted by CARacic
But when are they going to bring gasoline direct injection to bikes?
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Good question (read this, but I forgot/lost the source/link)
Direct Gasoline Injection for Motorcycles
The fuel injection in motorcycles has a big influence on the behavior of the engine in terms of performance, emission, fuel economy and driveability.During the last years Direct Gasoline Injection (DGI) has been developed to readiness for start of production and has been introduced to several passenger cars. The major aim when talking about DGI for passenger cars is the improvement of fuel consumption.
However motorcycles have to fulfil different target specifications which are comparable to application of DGI for racing.The potential for performance increase by using DGI is shown in picture 'Potential for performance increase by using DGI'. Beside a slightly increase in engine power DGI offers additional potential to improve the engine behaviour.
Improvements by using DGI:
higher engine performance due to increased volumetric efficiency
improved driveability
possibility of fast traction control
improved emission behavior by avoidance of wall film (picture 'Wall film of engine with PFI') and reduced HC emissions during valve overlap (picture 'HC emissions during valve overlap')improved fuel economy, extended range
A special challenge when applying DGI on motorcycle engines is the wide engine speed range of these engines.The following pages describe the characteristics to be taken into consideration when applying DGI on high performance and high revving motorcycle engines.
High Revving DGI Engines
In order to utilize the whole potential of DGI and to avoid any shortcomings the injection has to take place in a certain window of the operation cycle. More precisely is has to be ensured that no moving parts like piston or valves are impinged by the injection spray and that there is sufficient time for mixture formation before ignition. These boundary conditions are shown in picture 'Optimal injection timing and limitations by piston impingement and homogenization problems due to late injection (PFI = Port Fuel Injection)'.
Above mentioned considerations lead to an optimal injection window for each engine operation point. Picture 'Injection timing' shows this window of opportunity and the resulting available injection time for full load operation over engine speed. Due to the limited time for injection at high engine speed a high flow rate of the injector is required to provide the amount of fuel which is required at wide open throttle (WOT) and rated speed. On the other hand at idle operation or low load a small amount of fuel has to be provided without major deviations. Therefore special injectors and a modulated fuel pressure are required see picture 'Dynamic range of injector'.
DGI - PFI
A comparison of Direct Gasoline Injection (DGI) and Port Fuel Injection (PFI) shows that both concepts offer advantages for certain operating conditions.
PFI provides a homogeneous mixture due to the longer time which is available for mixture preparation. This ensures a good and stable combustion. As already mentioned DGI is advantageous in terms of driveability and transient engine behavior, leads to an increased volumetric efficiency, ensures lower emissions and a higher compression ratio can be realized which leads to a higher performance.
So it is logically to make use of the advantages of both concepts by a combination of DGI and PFI. In picture 'Optimal ration between DGI and PFI for maximum performance' the optimal ratio between DGI and PFI for maximum engine performance and the possible performance increase for one operating point by DGI - PFI compared to DGI only or PFI only is shown. This ratio is different for each operating point. The possible performance increase over engine speed by DGI - PFI is described in picture 'Performance increase by DGI - PFI'.
Picture 'DGI - PFI engine concept' shows a V2 engine concept with one top feed injector and one direct injector per cylinder. The direct injector is placed under the intake port between the intake valves.
Using two injectors is also advantageous to cover the required dynamic range from idle operation to wide open throttle at rated speed.
Driveability - Traction Control
A precondition for a fast lap time of a motorcycle is an engine which can be controlled by the rider easily. The behavior of the engine is influenced by the engine concept, firing order and various devices which give the possibility to realize a traction control. One example is an electronic throttle actuation (drive by wire) which offers the possibility to overrule the rider’ s input via the throttle grip.
Further solutions to realize a traction control are enleanment of the mixture, spark retardation and retardation of start of injection (SOI) of a direct injected engine.
When varying these parameters it has to be considered that the exhaust gas temperature does not exceed a certain limit. As shown in picture 'Fast traction control by varying of different parameters' SOI retardation of a DGI engine provides the widest adjustment range before the limitation given by the exhaust gas temperature is reached. Therefore DGI offers the most effective fast traction control.
Beside the target to achieve the fastest lap time a traction control is also a safety feature for less experienced riders. Under consideration of the steadily increasing performance of motorcycles offered on the market this feature may become indispensable in the near future.
Generally DGI leads to an improved driveability since the transient engine operation can be controlled easier. The reason is very simple. DGI provides the fuel where it is needed - in the combustion chamber. Therefore the element of uncertainty caused by the wall film (picture 'Area covered by wall film; 4 - stroke engine with PFI') in the intake ports is eliminated.
Design Concepts
Naturally aspirated high revving high performance engines are characterized by some characteristic design features. In order to achieve the desired performance optimized ports, a compact combustion chamber with central spark plug position and maximized valve size are necessary preconditions.
When applying an injector for direct injection it has to be considered that above mentioned design features are not influenced negatively. Depending on the layout of the cylinder head the injector position has to be optimised under consideration of the above mentioned boundary conditions. The analysis of various injector positions leads to the result that the optimal injector position for a 4 - valve engine is between the intake valves and below the intake port. A steep intake port as it is common for high performance engines is very advantageous for this layout. Furthermore it has to be considered that the shape of the combustion chamber is not disturbed by the application of the injector.
The fine tuning of the injector position and the inclination of the injector has to ensure that no impingement of the spray on cylinder wall and piston occurs. Special attention has to be paid on the moving parts like piston and valves.
The consideration of these guidelines during the design is imperative to avoid oil dilution, soot formation and carbon deposits and to ensure a trouble free engine operation.
During the design many accompanying work steps like simulation, hardware test and flow tests ensure an optimized engine design.