Carburated gasoline engines have the following disadvantages:
- Non uniform distribution of mixture in multi cylinder engines and hence loss of thermal efficiency/ higher exhaust emissions.
- Loss of volumetric efficiency due to restrictions for the mixture flow and possibility of back firing.
Due to the drawbacks of carburetion, Injection of fuel into the combustion chamber is being employed of late. The direct injection can be of continuous type or timed type. It has the following merits:
- Increased Volumetric efficiency
- Better thermal efficiency
- Lower Exhaust Emissions
- High quality fuel distribution
But DI engines are expensive than Carburetor type, since additional fuel handling systems are incorporated.
I want to add some points to those of Anand.
General advantages of fuel injection in comparison with carburetor:
- Possibility to consider temperature and air pressure (e.g. for cold start)
- Possibility of exhaust emission control by use of a lambda sensor (e.g. for stochiometric combustion and controlled catalytic conversion).
- No problems with carbonizing nozzles and float chamber.
- Possibility of engine map programming with a certain degree of freedom.
Challenges of direct fuel injection:
- Mixture preparation in cylinder, because of short timestep (especially in case of higher rpm).
- High costs because of high pressure components.
- Particulate emissions increase in comparison with indirect fuel injection.
Kind regards,
Mario
Dear Ajinkya,
For GDI please have a look at the attached paper and presentation.
Regards,
Andreas
http://www.ijrame.com/vol2issue3/V2i333.pdf
http://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1024&context=auto_pres
An ideal carburetor system should supply equal quality and quantity mixture for the all cylinders of a multi-cylinder automotive engine. but---- the inlet valves (or ports) of multi-cylinder gasoline engine are connected to a single carburetor through inlet manifold(s), therefore the distance between the carburetor and a specific inlet port varies. Ex: In a 6-cylinder engine, air-fuel mixture has to travel a long path to reach 6th cylinder from the carburetor located centrally. Therefore, the friction will influence on the quality (A/F ratio, Droplet size, etc.,) of the air-fuel mixture. Therefore, the carburetor system fails to supply uniform mixture (quantity as well as quality) for all the cylinders as demanded by the engine (to meet the variable load and speeds conditions). This leads to engine noise, vibration, high levels of exhaust emissions and low performance of the engine.
Air-fuel mixture should not be condensed while passing through an inlet-manifold (from carburetor to valve port). In cold regions/climatic conditions(winter, raining, etc,), the inlet manifold was surrounded by low temperature air. Therefore the air-fuel vapor mixture (prepared by the carburetor) passing through an inlet-manifold gets condensed before reaching the inlet valve/port/cylinder. This leads to poor combustion and causing more exhaust emissions such as HC, & CO and more-fuel consumption. Therefore to reduce (or to avoid) the condensation, the process of mixture formation should occur close to the cylinder, this is what is called port injection (PI) or Multi-Port Fuel Injection (MPFI).
Advantages of GDI:
Fast acceleration and deceleration (due to shortage of travel path)
Increased rate of vaporization leads to near-complete combustion: During port injection, the fuel-spray falls on hot inlet-valve (heated by in-cylinder gases), which increases the vaporization further.
Engine starts in single-cranking (in case of carburated engines, engine starts after two or three crankings)
No need of choke operation in winter (Manual operation of choke of a carburetor is required in two-wheels only)
Hellow,and could you please give me the full text of the "Washers to Reduce Vibration and Noise From the Injection Molding Process" --an asking hlep from China. My emaill is [email protected]
carburated gasoline engine is even older and does not really overlap with GDI.
Before 1996, majority of the gasoline engines are carburated. Then there is the transition to PFI (port fuel injection) and MPFI (multi-port). The uneven cylinder to cylinder distribution is eliminated by this. And we can control the injected mass directly and precisely. For example, 0 injected mass when going downhill.
Then there is the transition from PFI to GDI. PFI can only do stoichiometric premixed mixture, while GDI can do a lot of other different things, such as stratified combustion, HCCI, etc.
In general, GDI has higher efficiency, better fuel economy, lower emissions.
The disadvantage would be some carbon build up, and slightly higher Particulate Matter emission than PFI.
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