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Posted on 3/26/2016 11:30:52 AM

In order to meed the demand of cleaner engine emissions, improved power, quieter operation and better fuel economy,the global vehicle manufacturers have developed the new generation of more efficient fuel injection systems.The unit injection system integrates the injection pump and nozzle into a single module.In other word,the accomplishment of fuel pressurization; injection timing, atomization and fuel distribution is done by using only one single component.


EUI,short for Electronic Unit Injector,are installed directly into the cylinder head above each combustion chamber. The injector is driven by the engine camshaft, most often directly through only a rocker lever as in the case of an overhead camshaft. This configuration is one of the most efficient hydraulic and mechanical fuel system arrangements providing the low parasitic losses. Actuating the injectors using an overhead camshaft permits the least amount of injection lag since there are no push-tubes to bend, injector lines to swell or delivery vales to lift. The short distance pressurized fuel travels means an absence of injection lag due to high-pressure fuel wave propagation found in PLN systems.Eliminating injection lag provides for precise injection timing and facilitates the most valuable attribute of these injectors - the highest spray in pressures of any fuel injection system. 
The function of electronic control of governing,timing and metering will help pressurize Electronic unit injectors which is made up of a number of basic components:
1.The spring-loaded plunger and barrel assembly to pressurize fuel inside the injector. 
2. A poppet valve, known also as a spill control valve or solenoid needle valve that regulates the build-up of pressure inside the injector.
3.An electric solenoid or cartridge valve that actuates movement of the poppet valve or needle valve. Linkage such as a stator or solenoid pin may also directly connect the solenoid to the poppet valve in some injectors. 
4.Fuel inlet and return passageways.The transfer pump provide the low-pressure fuel to the fuel inlet.The return passageway permits fuel which has circulated through the injector to flow back to the suppy tank.Since the injector is located in the cylinder head,and pressurization of fuel creates heat, it is important that a steady circulation of fuel passes through the injector removes heat. 
5.The nozzle valve at the injector tip is like a conventional nozzle valve opening at 4,500-psi to 5000-psi in most injectors. This provides for improved atomization and crisp beginning and end of injection characteristics.
How EUI work?
Regardless of the type of unit injector, EUI’s share common operating principles.An electrical signal is sent to the unit injector’s solenoid-actuated spill/poppet valve system to deliver the correct quantity fuel at the precise time required to by ECM algorithms and fuel maps. Injection is accomplished by switching an integrated solenoid valve on and off. Injection delivery quantity is a function of both electrical signal time and plunger velocity. The time or duration the injector solenoid is electrically actuated is one factor determining the injection quantity.It means that the fuel quantity injected is controled by the signal time applied to the solenoid.However, the faster the engine rotates, the greater the distance of plunger travel per unit of time.Consequently, more fuel is injected at higher engine speed if the time the solenoid is electrically actuated remains constant.
Fuel passages integrated into the cylinder head supply low-pressure fuel from the supply/transfer system to each injector. Supply circuits are arranged to ensure consistent fuel temperature between injectors.  
Fuel flows into internal passageways and the pressure chambers within the injector to cool the injector and purge any vapour from the fuel circuits. 
The injector plunger, driven by the camshaft, moves through a stroke fixed by the injector plunger travel adjustment. On its upward stroke, the low-pressure fuel supplied to the injector fills the cavity created beneath the plunger. Fuel can enter this cavity through the open spill, poppet or needle valve. 
The injector plunger will begin its downward stroke and fuel below the injector plunger will be forced out of the injector through the fuel return passageway.  Without a signal from the ECM to the solenoid the plunger will bottom out it stroke and the suction cycle will repeat with no pressurization or delivery of fuel. 
When the ECM does send an electrical signal to the solenoid, the poppet, spill or needle valve will close the fuel return passageway causing trapped fuel to pressurize beneath the injector plunger. As the plunger continues its downward stroke, fuel pressure builds in the high-pressure passages, the nozzle valve opens and fuel injection begins. Maximum injection pressures occur near the end and not the beginning of the plunger travel,this point usually coincides with the time the solenoid valve is de-energized.
Bosch is now working on developing unit injection system (UIS) called the Coaxial Variable Nozzle UIS in order to make diesel engine quiter and cleaner burning  through enhanced abilities to rate shape injection over wider engine speed and load conditions. It will make difference in the arrangement, number, diameter and shape of the injection spray holes,compared to the old generation of unit injector.The injector uses an electrically operated solenoid valve however, it operates two nozzle valves sharing a common axis or, coaxial. The nozzle valves open two rows of spray holes. A lower set of spray holes delivers fuel at a small injection rate at the start of the combustion process. Like pilot injection, this set of orifice produces a gentler, less noisy,combustion pressure rise. Under light load operation, mixture formation improves resulting in significantly reduced emission levels. Evaluation of emissions demonstrates particulate and nitrogen oxide reductions of between 25 and 40 %. A second row of spray holes with a higher flow rate are opened when injection delivery volume increases.This configuration permits the use of pre-injection over a wide range of engine speed and load conditions, resulting in lower particulate emissions. In aftermarket,the common rail parts manufacturer - China Balin Parts Plant is also making efforts to make research on this.You might see their achievement sooner or later.
Electronic Unit Pumps (EUP’s) 
EUP,short for Electronic Unit Pump.
Also referred to as a unit pump system (UPS), unit injection pumps combine elements of pump line nozzle injection systems and unit injectors. Each cylinder will use a separate engine camshaft driven high-pressure pump to pressurize fuel for injection.High-pressure fuel line connect the pump to the nozzle.The pump operates using principles similar to the unit injector. A roller reduces friction between the pumping element and dedicated camshaft lobe. EUP injection systems have permitted the adaptation of high pressure electronically managed injection system to engines previously using inline pump injection systems without extensive engine modifications. 
Control of the solenoid by the engine ECM is identical to the unit injector.Slightly lower injection pressures are used by EUP’s and the use of the line prevents the use of electronic rate shaping the unit injectors are capable of. 
Metering and timing of the fuel is regulated by the electronic engine management system,which actuates the solenoid poppet control valve to stop the free flow of fuel through the injector unit pump. When the solenoid poppet valve closes, fuel is trapped in the injector unit pump plunger. 
Fuel supply to each EUP is provided by a low-pressure supply transfer system.The supply fuel pump delivers fuel at low pressure to the fuel filtera, then to the individual fuel injection pumps. The continuous fuel flow through the injector unit pump prevents air pockets from collecting in the fuel system and cools those injector unit pump parts subjected to high combustion temperatures. A fuel return line collects unused fuel circulating through the pumps and empties it back into the fuel tank.
The use of the flange mount on the side of the engine block above the camshaft provides for convenient of service or field replacement of pumps.

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