**Abstract**

The chapter presents the application of variable compression ratio VCR technology for an internal combustion engine. The engine's overall construction has been designed as the deep reconfiguration of liquid-cooled, heavy-duty diesel engine of type IFA 4 VD 14,5/12-1 SRW. An eccentric shaft-based sliding mechanism has been used for changing position of engine cylinder head assembly. By ensuring a high stiffness of the engine layout together with additional sliding mechanism, the combustion chamber volume of the engine can be changed precisely without changing the displacement of the cylinders. In result, the engine compression ratio can be continuously varied during normal engine operation from the value of 19:1 down to 9:1.

**Keywords:** heavy-duty diesel engine, compression ratio, variable compression ratio technology, eccentric mechanism, internal combustion engine

## **1. Introduction**

The desire to limit the adverse external effects associated with the development of motorization and transport, mainly based on the reciprocating internal combustion engine as the primary power source, reveals primarily with limitation the allowable level of emissions of harmful substances in the exhaust gases, that is, carbon monoxide, CO; hydrocarbons, HC; nitrogen oxides, NOx; and particulate matter, PM. Moreover, in the perspective of growing global warming phenomenon and dropping resources of liquid fuels, particular attention is paid to the reduction of fuel consumption and thus CO2 emission. Unfortunately, the physical and chemical rules of working processes in piston engines do not allow to meet all the above requirements in a simple manner. Despite significant progress made in recent years, further improvement of the ecological and energetic parameters of reciprocating engines requires further changes in their design, covering practically all functional systems.

One of the more effective paths, although at the current stage of development is still having many technical and operational difficulties, is the construction of engines in which the compression ratio becomes a regulation parameter and can be

changed continuously in a wide range and relatively short time. In a conventional engine, the compression ratio—the ratio of the smallest to the largest cylinder volume at piston top dead center positions—is constant and determined by the geometry of the cylinder and crank mechanism. The new technology called variable compression ratio, and marked with the VCR symbol, completely changes the previously unchanged feature of the engines. Many companies have noticed significant potential hidden in variable compression systems and focused their entire attention on finding ways to apply and use this feature. Therefore, over the last years, there has been a growing interest in this type of innovative construction.

### **1.1 Potential application area of VCR technology**

The origination of the idea of variable compression ratio was the desire to use for the engine supplying fuels with different properties; it is the so-called flex-fuel capability. Although it is still a valuable property, currently in the development of internal combustion engines, a special emphasis is placed on reducing fuel consumption, and thus CO2 emissions, as well on reducing the emission of harmful exhaust components—carbon monoxide, hydrocarbons, nitrogen oxides, or particulates.

Global automotive industry as well science and research institutions involved in the development of VCR technology say about the potential for reducing fuel consumption by using a variable compression ratio in engines of different capacity. Significant economic benefits are particularly visible when variable compression ratio technology is used for high-power engines. It is significant also if these are naturally aspirated or boosted engines with direct injection (DFI) and variablecontrolled valve actuation (VVA). **Figure 1** illustrates the potential benefits for the individual and combined use of these solutions.

higher boosting pressure. Reduced stroke volume can be also obtained, among others, by reducing the number of cylinders. It means the mechanical and thermal losses are reduced, as well cylinder charge exchange losses, the so-called "pumping" losses too. At the same, the overall efficiency of the engine increases. On the other hand, an increase in the boost pressure requires a reduction of geometric compression ratio to avoid adverse phenomena in the combustion process. Due to the direct relationship with the cycle efficiency, it is preferred to use as high compression ratio as possible. So, the compression ratio value must be a compromise between achieving the high thermal efficiency of the cycle and other restrictions, such as: knock limit, level of mechanical and/or thermal loads, maximum rate of pressure rising (engine run hardness), etc. However, these limitations are only in force at high engine loads, especially at high boosting. In conventional engines, the compression ratio is optimized and finally determined for these operating conditions. However, this is not a significant area of their usual operation. At low and moderate loads, the compression ratio could be much higher, giving increased operational efficiency of the vehicle. Therefore, the VCR technology enables a significant extension of the "downsizing" range, allowing further reduction of the displacement volume and the use of even higher boosting pressures. It is estimated that this method of adjusting the working parameters of the spark-ignition engine can result in a reduction in the fuel consumption by up to 30% without a significant increase of toxic exhaust

*Application of Variable Compression Ratio VCR Technology in Heavy-Duty Diesel Engine*

*DOI: http://dx.doi.org/10.5772/intechopen.93572*

*The foreseen decrease of CO2 emissions, thanks to the use of VCR and VVA technologies [1].*

Finally, the next area of using VCR technology is the possibility of effective implementation of advanced, low-temperature LTC combustion processes (lowtemperature combustion). They are characterized by extremely low emission levels of toxic compounds as a result of high complementarity of the combustion phase, but conducted under conditions with reduced charge temperature. Especially, a lack of temperature gradients in the combustion chamber is the main cause of avoiding nitrogen oxides' formation. There are, however, certain difficulties in obtaining low-temperature combustion stability under the high engine loads. Within this range of engine operation, a new VCR variable compression ratio technology exhibits a promising application potential, thanks to the high ability in moderating

compound emission [1].

**115**

**Figure 2.**

Significantly, greater benefits in the field of fuel economy and engine ecology can be obtained by combining the VCR and VVA variable valve actuation systems (**Figure 2**). The use of these systems allows, for example, the implementation of the Atkinson working cycle and the using engines of smaller dimensions with maintained high operational parameters, that is, according to the idea of "ultra-downsizing."

"Downsizing" is a relatively new development trend of piston engines, which gives a response to strong pressure on reducing fuel consumption and improving the overall engine efficiency. The idea of downsizing is to reduce the cubic capacity of the powerdrives and increase the power ratio, mainly by using still higher and

**Figure 1.** *The predicted increase in engine fuel economy with using VCR technology [1].*

*Application of Variable Compression Ratio VCR Technology in Heavy-Duty Diesel Engine DOI: http://dx.doi.org/10.5772/intechopen.93572*

**Figure 2.**

changed continuously in a wide range and relatively short time. In a conventional engine, the compression ratio—the ratio of the smallest to the largest cylinder volume at piston top dead center positions—is constant and determined by the geometry of the cylinder and crank mechanism. The new technology called variable compression ratio, and marked with the VCR symbol, completely changes the previously unchanged feature of the engines. Many companies have noticed significant potential hidden in variable compression systems and focused their entire attention on finding ways to apply and use this feature. Therefore, over the last years, there has been a growing interest in this type of innovative construction.

*Numerical and Experimental Studies on Combustion Engines and Vehicles*

The origination of the idea of variable compression ratio was the desire to use for

Global automotive industry as well science and research institutions involved in

Significantly, greater benefits in the field of fuel economy and engine ecology can be obtained by combining the VCR and VVA variable valve actuation systems (**Figure 2**). The use of these systems allows, for example, the implementation of the

"Downsizing" is a relatively new development trend of piston engines, which gives a response to strong pressure on reducing fuel consumption and improving the overall engine efficiency. The idea of downsizing is to reduce the cubic capacity of the powerdrives and increase the power ratio, mainly by using still higher and

Atkinson working cycle and the using engines of smaller dimensions with maintained high operational parameters, that is, according to the idea of

*The predicted increase in engine fuel economy with using VCR technology [1].*

the engine supplying fuels with different properties; it is the so-called flex-fuel capability. Although it is still a valuable property, currently in the development of internal combustion engines, a special emphasis is placed on reducing fuel consumption, and thus CO2 emissions, as well on reducing the emission of harmful exhaust components—carbon monoxide, hydrocarbons, nitrogen oxides, or particulates.

the development of VCR technology say about the potential for reducing fuel consumption by using a variable compression ratio in engines of different capacity. Significant economic benefits are particularly visible when variable compression ratio technology is used for high-power engines. It is significant also if these are naturally aspirated or boosted engines with direct injection (DFI) and variablecontrolled valve actuation (VVA). **Figure 1** illustrates the potential benefits for the

**1.1 Potential application area of VCR technology**

individual and combined use of these solutions.

"ultra-downsizing."

**Figure 1.**

**114**

higher boosting pressure. Reduced stroke volume can be also obtained, among others, by reducing the number of cylinders. It means the mechanical and thermal losses are reduced, as well cylinder charge exchange losses, the so-called "pumping" losses too. At the same, the overall efficiency of the engine increases. On the other hand, an increase in the boost pressure requires a reduction of geometric compression ratio to avoid adverse phenomena in the combustion process. Due to the direct relationship with the cycle efficiency, it is preferred to use as high compression ratio as possible. So, the compression ratio value must be a compromise between achieving the high thermal efficiency of the cycle and other restrictions, such as: knock limit, level of mechanical and/or thermal loads, maximum rate of pressure rising (engine run hardness), etc. However, these limitations are only in force at high engine loads, especially at high boosting. In conventional engines, the compression ratio is optimized and finally determined for these operating conditions. However, this is not a significant area of their usual operation. At low and moderate loads, the compression ratio could be much higher, giving increased operational efficiency of the vehicle. Therefore, the VCR technology enables a significant extension of the "downsizing" range, allowing further reduction of the displacement volume and the use of even higher boosting pressures. It is estimated that this method of adjusting the working parameters of the spark-ignition engine can result in a reduction in the fuel consumption by up to 30% without a significant increase of toxic exhaust compound emission [1].

Finally, the next area of using VCR technology is the possibility of effective implementation of advanced, low-temperature LTC combustion processes (lowtemperature combustion). They are characterized by extremely low emission levels of toxic compounds as a result of high complementarity of the combustion phase, but conducted under conditions with reduced charge temperature. Especially, a lack of temperature gradients in the combustion chamber is the main cause of avoiding nitrogen oxides' formation. There are, however, certain difficulties in obtaining low-temperature combustion stability under the high engine loads. Within this range of engine operation, a new VCR variable compression ratio technology exhibits a promising application potential, thanks to the high ability in moderating

the thermodynamic conditions in the combustion chamber, which determine the initiation and course of combustion process.
