CRDI Seminar Report

CRDI Engines

2012

CHAPTER 1: INTRODUCTION 1.1 FUEL INJECTION IN DIESEL ENGINES Mechanical and electronic injection

Older engines make use of a mechanical fuel pump and valve assembly which is driven by the engine crankshaft, usually via the timing belt or chain. These engines use simple injectors which are basically very precise spring-loaded valves which will open and close at a specific fuel pressure. The pump assembly consists of a pump which pressurizes the fuel, and a disc-shaped valve which rotates at half crankshaft speed. The valve has a single aperture to the pressurized fuel on one side, and one aperture for each injector on the other. As the engine turns the valve discs will line up and deliver a burst of pressurized fuel to the injector at the cylinder about to enter its power stroke. The injector valve is forced open by the fuel pressure and the diesel is injected until the t he valve rotates out of alignment and the fuel pressure to that injector is cut off. Engine speed is controlled by a third disc, which rotates only a few degrees and is controlled by the throttle lever. This disc alters the width of the aperture through which the fuel passes, and therefore how long the injectors are held open before the fuel supply is cut, controlling the amount of fuel injected. This contrasts with the more modern method of having a separate fuel pump (or set of pumps) which supplies fuel constantly at high pressure to each injector. Each injector then has a solenoid which is operated by an electronic control unit, which enables more accurate control of injector opening times depending on other control conditions such as engine speed and loading, resulting in better engine performance and fuel economy. This design is also mechanically simpler than the combined pump and valve design, making it generally more reliable, and less noisy, than its i ts mechanical counterpart. Both mechanical and electronic injection systems can be used in either direct or indirect injection configurations. Indirect injection

An indirect injection diesel engine delivers fuel into a chamber off the combustion chamber, called a prechamber, where combustion begins and then spreads into the main combustion chamber. Direct injection

Modern diesel engines make use of one of the following direct injection methods: 1) Distributor pump direct injection

The first incarnations of direct injection diesels used a rotary pump much like indirect injection diesels, however the injectors were mounted directly in the top of the combustion chamber rather than in a separate pre-combustion chamber. Examples are vehicles such as the Ford Transit and the Austin Rover Maestro and Montego with their Perkins Prima engine. The problem with these vehicles was the harsh noise that they made and particulate (smoke) emissions. This is the reason that in the main this

Department of Automobile and Mechanical Engineering, ITM University

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type of engine was limited to commercial vehicles (the notable exceptions being the Maestro, Montego and Fiat Croma passenger cars). Fuel consumption was about 15% to 20% lower than indirect injection diesels which for some buyers was enough to compensate for the extra noise. 2) Common rail direct injection

In older diesel engines, a distributor-type injection pump, regulated by the engine, supplies bursts of fuel to injectors which are simply nozzles through which the diesel is sprayed into the engine's combustion chamber. In common rail systems, the distributor injection pump is eliminated. Instead an extremely high pressure pump stores a reservoir of fuel at high pressure - up to 1,800 bar (180MPa) (180MPa) - in a "common rail", basically a tube which in turn branches off to computer-controlled injector valves, each of which contains a precision-machined nozzle and a plunger driven by a solenoid. Most European automakers have common rail diesels in their model lineups, even for commercial vehicles. Some Japanese manufacturers, such as Toyota, Nissan and recently Honda, have also developed common rail diesel engines. 1) Unit direct injection

This also injects fuel directly into the cylinder of the engine. However, in this system the injector and the pump are combined into one unit positioned over each cylinder. Each cylinder thus has its own pump, feeding its own injector, which prevents pressure fluctuations and allows more consistent injection to be achieved. This type of injection system, also developed by Bosch, is used by Volkswagen AG i n cars (where it is called Pumpe Düse - literally "pump nozzle"), and most major diesel engine manufacturers, in large commercial engines (Cat, Cummins, Detroit Diesel). With recent advancements, the pump pressure has been raised to 2,050 bar (205 MPa), MPa), allowing injection parameters similar to common rail systems.

1.2 CRDI (COMMON RAIL DIESEL INJECTION)

CRDI stands for Common Rail Direct Injection meaning, direct injection of the fuel into the cylinders of a diesel engine via a single, common line, called the common rail which is connected to all the fuel injectors. Whereas ordinary diesel direct fuel-injection systems have to build up pressure anew for each and every injection cycle, the new common rail (line) engines maintain constant pressure regardless of the injection sequence. This pressure then remains permanently available throughout the fuel line. The engine's electronic timing regulates injection pressure according to engine speed and load. The electronic control unit (ECU) modifies injection pressure precisely and as needed, based on data obtained from sensors on the cam and crankshafts. In other words, compression and injection occur independently of each other. This technique allows fuel to be injected as needed, saving fuel and lowering emissions.


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More accurately measured and timed mixture spray in the combustion chamber significantly reducing unburned fuel gives CRDi the potential to meet future emission guidelines such as Euro V. CRDi engines are now being used in almost all MercedesBenz, Toyota, Hyundai, Ford and many other diesel automobiles.

Figure 1 Schematic diagram of CRDI


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CHAPTER 2: LITERATURE REVIEW 2.1 A method for Combustion Phasing Control use Cylinder Pressure measurement in a CRDI Diesel Engine

The start of combustion (SOC) in the combustion chamber has a considerable influence upon all performances of the engine. In this paper, cylinder pressure was investigated as a means for the closed-loop SOC control of a common-rail direct injection (CRDI) diesel engine. In order to detect the SOC, the crank angle position where the difference pressure became 10 bar was selected as the pressure variable. Using this pressure variable as a feedback variable, an adaptive feed forward control was proposed. The feed forward controller consisted of the radial basis function network (RBFN) and the feedback error learning method, which was used for the training of the network. The proposed SOC control strategy showed a far better regulation performance than that of the linear feedback controller. A further extension of the strategy based on the individual cylinder pressure feedback, the individual cylinder SOC control strategy, effectively reduced cylinder-by-cylinder cylinder-by-cy linder SOC variation in steady and transient engine operations. [1] 2.2 New Direct Fuel Injection Engine Control Systems for Meeting Future Fuel Economy Requirements and Emission Standards

Recently, the need to reduce CO2 levels has made increased fuel economy an urgent matter in Japan and Europe. Use of the highly efficient diesel engine is expected to increase and measures against emissions such as soot are a major problem. Gasoline engines, on the other hand, are more sustainable in terms of exhaust emissions, and are steadily approaching the diesel engine in terms of fuel economy as well. Since introducing a direct fuel injection engine control system in 1997, the Hitachi Group has continued to develop and manufacture system control and the main components for it, and now we are expanding into Europe as well. [2]

Figure 2 Basic Structure and components of Direct Fuel Injection System


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CHAPTER 3: BASIC PRINCIPLE OF CRDI 3.1 OVERVIEW

Compared with petrol, diesel is the lower quality fuel from petroleum family. Diesel particles are larger and heavier than petrol, thus more difficult to pulverize. Imperfect pulverization leads to more unburned particles, hence more pollutant, lower fuel efficiency and less power. Common-rail technology is intended to improve the pulverization process. To improve pulverization, the fuel must be injected at a very high pressure, so high that normal fuel injectors cannot achieve it. In common-rail system, the fuel pressure is implemented by a very strong pump instead of fuel injectors. The high-pressure fuel is fed to individual fuel injectors via a common rigid pipe (hence the name of "commonrail"). In the current first generation design, the pipe withstands pressures as high as 1,600 bar or 20,000 psi. Fuel always remains under such pressure even in stand-by state. Therefore whenever the injector (which acts as a valve rather than a pressure generator) opens, the high-pressure fuel can be injected into combustion chamber quickly. As a result, not only pulverization is improved by the higher fuel pressure, but the duration of fuel injection can be shortened and the timing can be more precisely controlled. Solenoid or piezoelectric valves make possible fine electronic control over the fuel injection time and quantity, and the higher pressure that the common rail technology makes available provides better fuel atomisation. In order to lower engine noise, the engine'selectronic engine'selectronic control unit can inject a small amount of diesel just before the main injection event ("pilot" injection), thus reducing its explosiveness and vibration, as well as optimising injection timing and quantity for variations in fuel quality, cold starting and so on. Some advanced common rail fuel systems perform as many as five injections per stroke. In common rail systems, a high-pressure pump stores a reservoir of fuel at high pressure up to and above 2,000 bars (29,000 psi). The term "common rail" refers to the fact that all of the fuel injectors are supplied by a common fuel rail which is nothing more than a pressure accumulator where the fuel is stored at high pressure. This accumulator supplies multiple fuel injectors with high-pressure fuel. This simplifies the purpose of the highpressure pump in that it only has to maintain a commanded pressure at a target (either mechanically or electronically controlled). The fuel injectors are typically ECU-controlled. When the fuel injectors are electrically activated, a hydraulic valve (consisting of a nozzle and plunger) is mechanically or hydraulically opened and fuel is sprayed into the cylinders at the desired pressure. Since the fuel pressure energy is stored remotely and the injectors are electrically actuated, the injection pressure at the start and end of injection is very near the pressure in the accumulator (rail), thus producing a square injection rate. If the accumulator, pump and plumbing are sized properly, the injection pressure and rate will be the same for each of the multiple injection events.


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3.2 PRESSURE CIRCUITS

Figure 3 Pressure circuits

LOW PRESSURE FUEL CIRCUIT Low pressure Fuel pump

Low pressure Fuel pump is either an electric fuel pump with pre-filter or a gear type fuel pump. The pump draws the fuel from the fuel tank and continually delivers the required quantity of fuel in the direction of high pressure pr essure fuel pump. Fuel Sender

It is located into the fuel tank and measures amount of fuel contained in fuel tank.


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Fuel Filter

It is located between low pressure fuel pump and high pressure fuel pump and filters the fuel delivered from the fuel tank.

HIGH PRESSURE FUEL CIRCUIT High pressure Fuel Pump

It compresses fuel up to 1600 bar and delivers the compressed fuel to common rail. Common Rail

It is connected with the high pressure fuel pump and the t he injectors by the high pressure fuel pipes. This rail stores the fuel compressed by the high pressure pump. The ECM controls the fuel pressure of the common rail by using the rail pressure sensor and the rail pressure regulator valve installed on the common rail. Injector

The injector injects the high pressure fuel stored into the common rail into t he cylin der by the ECM control signal. High pressure fuel pipe

High Pressure Fuel Pipe is a channel in high pressure Fuel Circuit consisting of the high pressure fuel pump, the common rails, and injectors. It is a steel tube which can withstand high frequency generated when the fuel pressure the maximum pressure or fuel injection stops.

3.3 INJECTION STAGES

Due to extremely quick reactions in millisecond range upto five separate injection process can be achieved per cycle. In addition to main injection process, pre and post processes are also possible. Pre Injection/Pilot Injection

During this stage a small amount of diesel is injected just before the main injection event thus reducing vibration as well and optimising injection timing and quantity for variation in fuel quality and cold starting. It moderates the acoustic hardness so called racking in the combustion process. Main Injection

It is the main event during which compression occurs and charge is i gnited thereafter. Post Injection

It injects small amount of fuel during the expansion phase thus creating small scale combustion after the normal combustion takes place. This further eliminates the unburned


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particles and also increases the exhaust flow temperature thus reducing the pre-heat time of the catalytic converter. In short, "post-combustion" cuts pollutants.

Figure 4 High pressure Injection

Figure 5 Injection Stages


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CHAPTER 4: COMPONENTS OF CRDI 4.1 PRE-SUPPLY PUMP

Figure 6 Pre-Supply Pump

The electric fuel pump comprises of: 1. Electric Motor 2. Roller-Cell Pump 3 .Non return valve

4.2 HIGH PRESSURE PUMP The high Pressure pump is the interface between the low pressure and high pressure stages. Its function is to make sure there is always alwa ys sufficient fuel under pressure available in all engine operating conditions. At the same time it must operate fort the entire service life of the vehicle. This includes providing a fuel reserve that is required for quick engine starting and rapid pressurization in the fuel rail. The high pressure pump constantly maintains a system pressure of upto 1600-2000 bar in the high pressure accumulator. As a result, the fuel does not have to be pressurized during the fuel injection cycle.

Figure 7 High Pressure Pump


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4.3 FUEL RAIL (HIGH PRESSURE ACCUMULATOR)

The function of high pressure accumulator is to maintain the fuel at high pressure. In so doing, the accumulator volume has to dampen pressure fluctuations caused by the fuel pulses delivered by the pump and the fuel injection cycles. This ensures that, when the nozzles open, the injection pressure remains constant. The fuel rail also acts as a fuel distributor.

Figure 8 Fuel Rail

4.4 PRESSURE LIMITING VALVE

The function of the pressure limiting valve is equivalent to that of a pressure relief valve. The pressure limiting valve limits the pressure in the fuel rail by opening a pressure outlet when the pressure exceeds the specific limit.

Figure 9 Pressure Limiting Valve


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4.5 NOZZLE (FUEL INJECTION)

A fuel injector is nothing but an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump, and it is capable of opening and closing many times per second. When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel -- to make as fine a mist as possible so that it can burn easily. The amount of fuel supplied to the engine is determined by the amount of time the fuel injector stays open. This is called the pulse width, and it is controlled by the ECU. The injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurized fuel to all of the injectors. Each injector is complete and self-contained with nozzle, hydraulic intensifier, and electronic digital valve. At the end of each injector, a rapid-acting solenoid valve adjusts both the injection timing and the amount of fuel injected. A microcomputer controls each valve's opening and closing sequence.

Figure 10 Fuel Injector

4.6 MICROCOMPUTER & SENSORS

The new direct-injection motors are regulated by a powerful microcomputer linked via CAN (Controller Area Network) data bus to other control devices on board. These devices exchange data. The engine's electrical controls are a central element of the


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common rail system because regulation of injection pressure and control of the solenoid valves for each cylinder - both indispensable for variable control of the motor - would be unthinkable without them. This electronic engine management network is a critical element of the common rail system s ystem because because only the speed and spontaneity of electronics can ensure immediate pressure injection adjustment and cylinder-specific control of the injector solenoid valves.

Figure 11 Microcomputer

Figure 12 Sensors val


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CHAPTER 5: METHOD OF OPERATION In the common rail pressure accumulator fuel injection system, the functions of pressure generation and the fuel injection are separate. The EDC electronics-control system controls the individual fuel injection components. 5.1 PRESSURE GENERATION

A continuously operating high pressure pump driven by the engine produces the desired injection pressure. As that pressure is stored in the pressure accumulator, it is largely independent independent of engine speed and injected fuel quantity. The speed of high pressure pump is directly proportional to the engine speed as it driven by a system with a fixed transmission ratio. Because of the almost uniform injection pattern the high pressure pump can be significantly smaller and designed for a lower peak drive system torque than conventional fuel injection system. 5.2 FUEL INJECTION

The nozzles nozzles inject the fuel directly into the engine’s combustion chambers. They are supplied by high pressure fuel lines connected to the fuel rail. A nozzle consists essentially of an injector nozzle and a fast switching solenoid valve that controls the injectors nozzle by means of mechanical actuators. The electronic engine control unit controls the solenoid valve. At a constant system pressure, the quantity injected is proportional to the length of time that the solenoid valve is open and thus entirely independent of the engine or pump speed (time based fuel injection system)

5.3 CONTROL

With the aid of range of sensors, the engine control unit records the accelerator-pedal position and the current status of engine and the vehicle. The data collected includes:       

The crankshaft angle of rotation. The camshaft speed The fuel rail pressure The charge air pressure The temperature of intake air, engine coolant and fuel. The mass of the air charge. The road speed of the vehicles etc. The control analyzes the input signal and calculates with in a split seconds the control signals required for the high pressure pumps, the nozzle and the other actuators. The later may include the exhaust gas re circulation valve or o r the charge air actuator. The extremely fast switching time demanded of the nozzles is achieved with a aid off optimized high pressure solenoid valves and special control methods. The position time system matches the start of injection to the rotation of the engine using the data from the crankshaft and the camshaft sensors. The electronic diesel control


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makes it possible to precisely meter the fuel injection. In addition, EDC offers potential for response. 5.4 ADDITIONAL FUNCTIONS

Additional control functions perform the task of reducing exhaust gas emission and fuel consumption or providing added safety and convenience. Some examples are:    

Control of exhaust gas re circulation. Charge air pressure control Cruise control Electronic immobilizer. Integration of EDC in an overall network of vehicle systems also opens a range of new possibilities (e.g. Data exchange with climate control system or the transmission control system)


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CHAPTER 6: ADVANTAGES, APPLICATIONS & FUTURE TRENDS 6.1 ADVANTAGES

S.No 1 2 3 4 5

6 7 8 9

Normal Diesel Engine Pressure range from 200-400 bar Indirect injection of fuel Noisy Engine Fuel Injection Pressure Varies Mechanical metering of fuel quantity Fuel Injection timing mechanically controlled by fuel injection pump High Fuel consumption at low engine speed High Emission at low engine speed More particulate emission

CRDI engine Uniform Pressure exceeding 1200 bar Direct Injection of high pressure fuel Less Engine Noise Fuel Injection Pressure Remain constant Electronically control metering of fuel

Electronically controlled injection timing & independent independent of engine speed Low fuel consumption at all engine speed Low emission at all engine speed Reduce particulate emission

6.2 APPLICATIONS

The pressure accumulator common rail fuel injection system for diesel engines with direct injection is used in following type of vehicles: 

 

Cars ranging from economy models with 3 cylinders 0.8 litre engine producing 30kw of power and 100 N-m torque, and with fuel consumption of 3.5 litres 100km to luxury sedans with 8 cylinders 3.9 litres engines developing 180kw of power and 560 N-m of torque. Light commercial; vehicle with power output of up to 30kw/cylinder Heavy duty trucks, railway locomotives and ships with engines producing upto 200kw/cylinder

The common rail system offers a significantly higher level of adaptability to engine design on the part of the fuel injection system than cam operated as evidenced by: 

Better fuel efficiency



Higher torque



Lower green house gas emission



Wide range of applications



High injection pressure



Variable injection timing


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6.3 FUTURE TRENDS 5.1 Ultra-High Pressure Common – Rail Rail Injection:

Newer CRDI engines feature maximum pressures of 1800 bar. This pressure is up to 33% higher than that of first-generation systems, many of which are in the 1600-bar range. This technology generates an ideal swirl in the combustion chamber which, coupled with the fuel-spray pattern and optimized piston head design, allows common-rail common-rail injectors’ superior fuel-spray the air/fuel mixture to form a perfect vertical vortex resulting in uniform combustion and greatly reduced NOx (nitrogen oxide) emissions. The system realizes high output and torque, superb fuel economy, emissions low enough to achieve Euro Stage IV designation and noise levels the same as a gasoline engines. In particular, exhaust emissions and Nox are reduced by some 50% over the current generation of diesel engines. 5.2 CRDI and Particle Filter:

Figure 13 Particle Filter

Particle emission is always the biggest problem of diesel engines. While diesel engines emit considerably less pollutant CO and Nox as well as green house gas CO2, the only shortcoming is excessive level of particles. These particles are mainly composed of carbon and hydrocarbons. They lead to dark smoke and smog which is very crucial to air quality of urban area, if not to the ecology system of our planet. Basically, Basically, particle filter is a porous silicon carbide unit; comprising passageways passageways which has a property of easily trapping and retaining particles from the exhaust gas flow. Before the filter


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surface is fully occupied, these carbon / hydrocarbon particles should be burnt up, becoming CO2 and water and leave the filter accompany with exhaust gas flow. The process is called regeneration. Normally regeneration takes place at 550° C. However, the main problem is: this temperature is not obtainable under normal conditions. Normally the temperature varies between 150° and 200°C when the driving in town, as the exhaust gas is not in full flow. The new common-rail injection technology helps solving this problem. By its high-pressure, precise injection during a very short period, the common-rail system can introduce a "postcombustion" by injecting small amount of fuel during expansion phase. This increases the exhaust flow temperature to around 350°C. Then, a specially designed oxidizing catalyst converter locating near the entrance of the particle filter unit will combust the remaining unburnt fuel come from the "postcombustion". combustion". This raises the temperature further to 450° C. The last 100°C required is fulfilled by adding an addictive called Eolys to the fuel. Eolys lowers the operating temperature of particle burning to 450° C, now regeneration occurs. The liquid-state liquid-state additive is store in a small tank and added to the fuel by pump. The PF unit needs to be cleaned up every 80,000 km by high-pressure water, to get rid of the deposits resulting from the additive.


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CHAPTER 7: CONCLUSION The seminar that I had taken is CRDI system from which we reached to the conclusion that CRDI technology revolutionized diesel engines and also petrol engines (by introduction of GDI technology). By introduction of CRDI a lot of advantages are obtained, some of them are: 

More power is developed.



Increased fuel efficiency. Reduced noise



More Stability.



Pollutants are reduced.



Particulates of exhaust are reduced.



Exhaust gas recirculation is enhanced.



Precise injection timing is obtained.



Pilot and post injection increase the combustion quality.



More pulverization of fuel is obtained.



A very high injection pressure can be achieved.



The powerful microcomputer makes the whole system more perfect. It doubles the torque at lower engine speeds.

The main disadvantage is that this technology increase the cost of the engine.Also this technology cant be employed to ordinary engines.


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REFERENCES a

b

[1] Maru Yoon , Kangyoon Lee , and Myoungho Sunwoo. “A method for combustion phasing control using cylinder pressure measurement in a CRDI diesel engine.” engine. ” Hyundai-Kia Motor Company, 772-1. [2] T. Shiraishi et al., “Study on Mixture Formation of Direct Injection Engines,” Transaction of Automotive Engineers of Japan, Inc. Vol. 33, No. 4 (Oct. 2002) in Japanese. [3] http://en.wikipedia.org/wiki/Common_rail. [4] Kouremenos D. A. and Hountalas D. T. Development and validation of a detailed fuel injection system simulation model for diesel engines. SAE Technical Papers, 01(0527), 1999. [5] Covington J. P. Modernizing the fixed-venturi fix ed-venturi carburettor. Automotive Engineering, 82(7), 1974.


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