05-12-2012, 04:47 PM
DEVELOPMENT OF MECHANICAL GASOLINE DIRECT INJECTION (GDI) ENGINES FOR 4 STROKE TWO WHEELERS
DEVELOPMENT OF MECHANICAL GASOLINE.pdf (Size: 423.19 KB / Downloads: 64)
ABSTRACT-
The general demand in the market today is for two wheelers with excellent fuel economy, superb power performance and cleaner & greener emissions. But the actual situation is somewhat contrary in the sense that the two wheeler generally bought by the public have characteristics which include very high levels of pollution caused by scavenging losses, un-economical operation because of fresh charge losses, less scope for lean operation and no control on the engine once the valves have closed. Therefore the goal of this paper is to design an injection system to achieve optimum emission values and noise levels. In addition this paper looks at improving fuel consumption and drivability independent of the operating point, which is implemented by a mechanical variable injection timing system. For this, the effect of different head designs on the exhaust gas emissions is analyzed initially. Also a light weight and compact Aluminum housing is designed for the pump – follower junction. This is directly attached to the overhead camshaft.
A new jerk type fuel injection pump was designed based on the differences in the physio-chemical properties of diesel and petrol. The characterization of the engine is done in carburetor mode for reference purpose. A characterization of the fuel injection pump was also carried out.
INTRODUCTION
There are an estimated 70-80 million two wheelers in the Asian Market. Two wheelers are characterized with high emissions levels that are primarily caused by “scavenging losses” produced when the fresh air/fuel mixture is used to flush the exhaust gases from the previous stroke out of the engine; over 35% of the fuel is typically lost in the scavenging process. The application of direct in-cylinder fuel injection (or “direct injection” – DI) can be used to reduce HC and CO emissions by over 70%. There is also a reduction in fuel consumption.
Figure 1 [1]
These are achieved through charge stratification under overall lean conditions, to increase volumetric efficiency and to reduce exhaust emissions. Charge Stratification leads to drastic reduction in throttling losses and reduction of wall heat losses. Compared to the Port Fuel Injection System we expect fuel savings of 15-20 % in GDI engines (Figure 2).
Fuel savings, Partial load operation [2]
Decreasing throttling in GDI engine reduces the charge cycle work by one-third in comparison to Port Fuel Injection. Minimizing wall heat loss in a DISI engine lowers the release of heat to the coolant water by approximately 60% because of lower process temperatures.
Several types of engine operations are possible with Direct Injection – Stratified Operation, Homogenous Operation and Dual Injection. Controlling Injection during the compression stroke prevents the mixture from being completely mixed in the combustion chamber before the moment of ignition resulting in the stratification of fresh charge. The homogeneous operation is used in the full load range & for lean operation in the partial load range.
Figure 3: Strategies in direct gasoline injection [3]
Dual injection is the distribution of the injection event at two points in time. The injection timing could be distributed between intake compression & exhaust cycle. However the mixture is generally inhomogeneous. There are several feasible design configurations for GDI engines depending on relative position of injector to the spark plug & piston crown shapes, the injector timing and air motion and mixture preparation strategy. They are classified as air-directed combustion method, wall directed method and jet- directed methods.
EXPERIMENTAL SETUP AND INSTRUMENTATION
We started the development of 4 stroke SI engine based on GDI technology with mechanical fuel injection by testing and analyzing the performance of a two stroke engine with injection. This was followed up with the design part for GDI technology for a 4 stroke engine.
The experimental rig (figure 4) contains a Bajaj Champion scooter engine, Mico Bosch Fuel Injector, a 5 kilowatt fuel injection pump and an MS housing to support the cam shaft driving the fuel injection pump. The above mentioned camshaft takes its drive from the crankshaft of the engine and reduces the rotational speed to half. The weight of the housing was 5.52 Kg and the weight of the
In this setup, the comparison of brake specific fuel consumption (bsfc), HC emissions, CO2 emissions and NOx emissions of piston heads having no cavity with piston heads having cylindrical, conical and spherical cavities was done using an exhaust gas analyzer. The objective of the experiment was to show the improvement in engine performance especially bsfc, with different heads. It is observed that the bsfc decreased with piston cavities, however CO2 and NOx emissions increased as expected. Ranking the piston cavities according to various performance parameters, the following qualitative results were obtained (Table 1).