1. Background

Perhaps the most graceful invention by humankind that ever had a greater impact on society, the economy, and the environment is the reciprocating internal combustion engine, in general, called the IC engine. For decades, this magnificent invention proved to play a vital role in the automobile system, used almost exclusively today. There are two types of internal combustion engines: spark ignition (SI) and compression ignition (CI). For the last decades, rapid improvements in the efficiency have been achieved on both types of IC engine.

Unfortunately, at present, there is a pressing need to develop advanced combustion engines that maximize the engine efficiency and totally mitigate the exhaust pollutants. Profound understanding of both SI and CI combustion principles has been achieved during the last decades to improve the efficiency and reduce the emissions. The conventional SI combustion, which is characterized by flame propagation in near-stoichiometric homogeneous mixtures, produces very low exhaust emissions in combination with a three-way catalytic converter but has a relatively low thermal efficiency, which is its main drawback.

CI combustion, on the other hand, that is characterized by the autoignition of a lean fuel-air mixtures, has a very high thermal efficiency; yet, it has very high soot and NOx (nitrogen oxide) emissions. Diesel engines typically produce lower carbon monoxide (CO) and unburned or partially burned hydrocarbons (HC) compared to the gasoline engines. However, NOx, which comprises nitric oxides and nitrogen dioxides, in addition to particulate matter (PM) or soot, is significant pollutant from diesel engines, which require proper control strategies as they pose adverse health and environmental impacts.

HCCI was introduced in 1983. Major obstacle in HCCI is its rapid heat release rate with a very high maximum pressure, which is detrimental to engine structure. In the effort of controlling the combustion in HCCI engines, technologies such as exhaust gas recirculation (EGR) and variable valve timing (VVT) are utilized to improve the controllability of HCCI combustion, which is used in the commercial HCCI engine such as skyActive technology (Mazda) and

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On the other hand, in an effort to find the best method for controlling HCCI combustion, the HCCI has evolved into various types of controlled autoignition-based engine (CAI) such as premixed charge compression ignition (PCCI) in 1995 [1] and reactivity controlled compression ignition (RCCI) engine in 2011 [2]. These methods are proven to be able to improve the operating range of CAI engine. However, there are no established methods that are proven to

Figure 2 depicts the differences in each combustion system control strategy. The CI system (Figure 2 (a)) creates a very high pressure inside the combustion chamber, and the fuel is directly injected to combust. SI system (Figure 2b)), on the other hand, forms a homogeneous mixture either by direct injection or by port injection before the mixture is ignited by a spark, whereas the HCCI engine (Figure 2 (c)) produces a homogeneous mixture by injecting the fuel during the intake stroke, and the mixture is autoignited due to the compression. HCCI combustion combines the best features of gasoline and diesel engines to produce diesel-like power and efficiency while maintaining gasoline-like soot free emissions within certain operating

The engine performance was limited to the part load conditions and controlling the combustion process was very problematic due to the autoignition being highly dependent on the

diesOtto engine (Mercedes).

Figure 1. Engine technology development.

limits.

be effective in controlling CAI engine.

The engine technologies are advancing at a significant rate during the last decades. The engine technology development timeline is depicted in Figure 1. The engine performance was the main priority in the first era of engine developments. Technologies such as turbocharger, port fuel injection, high compression ratio, direct fuel injection, and engine lightweight material were the technologies that are focusing on increasing the engine power output to its maximum capabilities. This early era was driven by the abundant amount of fuels relative to its low demand as the automobile was still an exclusive technology.

The second era of the engine technology development was mainly driven by increasing concern about exhaust emissions and efforts in achieving low fuel consumption. In the earlier technologies, efficiency was improved and the engine downsizing was the primary target of the engine development. Homogeneous charge compression ignition (HCCI) engine is one of the promising alternatives in order to achieve these objectives.

The spark ignition engine (SI) and compression ignition engine (CI) are the established engine technologies, and each have their advantages and disadvantages. SI has a faster response and low emissions yet low efficiency, while CI offers high efficiency and low fuel consumption yet higher emissions and slower response. This makes the development of the SI and CI engine followed different approaches. Nevertheless, the main objective of an engine is mainly to achieve high performance, high efficiency with low emissions. In order to achieve this goal,

Reactivity Controlled Compression Ignition (RCCI) of Gasoline-CNG Mixtures http://dx.doi.org/10.5772/intechopen.72880 53

Figure 1. Engine technology development.

1. Background

52 Improvement Trends for Internal Combustion Engines

Perhaps the most graceful invention by humankind that ever had a greater impact on society, the economy, and the environment is the reciprocating internal combustion engine, in general, called the IC engine. For decades, this magnificent invention proved to play a vital role in the automobile system, used almost exclusively today. There are two types of internal combustion engines: spark ignition (SI) and compression ignition (CI). For the last decades, rapid improve-

Unfortunately, at present, there is a pressing need to develop advanced combustion engines that maximize the engine efficiency and totally mitigate the exhaust pollutants. Profound understanding of both SI and CI combustion principles has been achieved during the last decades to improve the efficiency and reduce the emissions. The conventional SI combustion, which is characterized by flame propagation in near-stoichiometric homogeneous mixtures, produces very low exhaust emissions in combination with a three-way catalytic converter but

CI combustion, on the other hand, that is characterized by the autoignition of a lean fuel-air mixtures, has a very high thermal efficiency; yet, it has very high soot and NOx (nitrogen oxide) emissions. Diesel engines typically produce lower carbon monoxide (CO) and unburned or partially burned hydrocarbons (HC) compared to the gasoline engines. However, NOx, which comprises nitric oxides and nitrogen dioxides, in addition to particulate matter (PM) or soot, is significant pollutant from diesel engines, which require proper control strategies as they pose

The engine technologies are advancing at a significant rate during the last decades. The engine technology development timeline is depicted in Figure 1. The engine performance was the main priority in the first era of engine developments. Technologies such as turbocharger, port fuel injection, high compression ratio, direct fuel injection, and engine lightweight material were the technologies that are focusing on increasing the engine power output to its maximum capabilities. This early era was driven by the abundant amount of fuels relative to its low

The second era of the engine technology development was mainly driven by increasing concern about exhaust emissions and efforts in achieving low fuel consumption. In the earlier technologies, efficiency was improved and the engine downsizing was the primary target of the engine development. Homogeneous charge compression ignition (HCCI) engine is one of

The spark ignition engine (SI) and compression ignition engine (CI) are the established engine technologies, and each have their advantages and disadvantages. SI has a faster response and low emissions yet low efficiency, while CI offers high efficiency and low fuel consumption yet higher emissions and slower response. This makes the development of the SI and CI engine followed different approaches. Nevertheless, the main objective of an engine is mainly to achieve high performance, high efficiency with low emissions. In order to achieve this goal,

ments in the efficiency have been achieved on both types of IC engine.

has a relatively low thermal efficiency, which is its main drawback.

demand as the automobile was still an exclusive technology.

the promising alternatives in order to achieve these objectives.

adverse health and environmental impacts.

HCCI was introduced in 1983. Major obstacle in HCCI is its rapid heat release rate with a very high maximum pressure, which is detrimental to engine structure. In the effort of controlling the combustion in HCCI engines, technologies such as exhaust gas recirculation (EGR) and variable valve timing (VVT) are utilized to improve the controllability of HCCI combustion, which is used in the commercial HCCI engine such as skyActive technology (Mazda) and diesOtto engine (Mercedes).

On the other hand, in an effort to find the best method for controlling HCCI combustion, the HCCI has evolved into various types of controlled autoignition-based engine (CAI) such as premixed charge compression ignition (PCCI) in 1995 [1] and reactivity controlled compression ignition (RCCI) engine in 2011 [2]. These methods are proven to be able to improve the operating range of CAI engine. However, there are no established methods that are proven to be effective in controlling CAI engine.

Figure 2 depicts the differences in each combustion system control strategy. The CI system (Figure 2 (a)) creates a very high pressure inside the combustion chamber, and the fuel is directly injected to combust. SI system (Figure 2b)), on the other hand, forms a homogeneous mixture either by direct injection or by port injection before the mixture is ignited by a spark, whereas the HCCI engine (Figure 2 (c)) produces a homogeneous mixture by injecting the fuel during the intake stroke, and the mixture is autoignited due to the compression. HCCI combustion combines the best features of gasoline and diesel engines to produce diesel-like power and efficiency while maintaining gasoline-like soot free emissions within certain operating limits.

The engine performance was limited to the part load conditions and controlling the combustion process was very problematic due to the autoignition being highly dependent on the

effective pressure due to the short combustion duration. Many methods and possibilities were proposed to control HCCI engines. In this process, the paradigm of creating an autoignition process from homogeneous charge is shifting to the method of controlling autoignition. The first development is the premixed charge compression ignition (PCCI). This concept was introduced by Aoyama et al. [1]. Gasoline was subjected into diesel-like environment with high compression ratio 17.4:1. A port injection method was used to create the premixed charge in the combustion chamber where the fuel is injected very close to the intake valve closing time as shown in

Reactivity Controlled Compression Ignition (RCCI) of Gasoline-CNG Mixtures

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The combination starts with gasoline and diesel as the low-reactive fuel and high-reactive fuel, respectively. It was found that RCCI combustion was able to operate in a wide range of engine loads with near-zero NOx and soot emissions, accepted pressure rise rate and high indicated efficiency. However, RCCI still could not achieve high load operation with power outputs comparable to CI engine. The combustion behavior of RCCI is somewhat still unpredictable. Further investigation on the important parameters in RCCI combustion control will improve the understanding of the combustion process of RCCI that leads to better control of the process

The premixed charge compression ignition (PCCI), reactivity charge compression ignition (RCCI), and spark-assisted HCCI are some of the established methods of controlling the autoignition process in an engine. All of these methods are categorized as CAI engines. Regardless of the limitations of the controlled autoignition (CAI)-based combustion system, CAI offers high efficiency [4], low fuel consumption [5], and low emission [6], which are the main aims of future engine development. The attributes that differentiate SI, CI, HCCI,

These earlier works are the basis of the controlled autoignition engine concept. The primary focus of the CAI combustion concepts is identifying the relevant influencing parameters as well as control parameters of this system to widen the operating range and improve the efficiencies. The need for a thorough understanding of the CAI combustion process initiates further discussion on the method to control its combustion. The next stage is to determine the engine parameters that have a direct effect on the combustion. As these steps are carefully defined, high efficiency, low fuel consumption, and low emissions internal combustion engines

Figure 3.

and better engine output.

are achievable (Table 2).

Figure 3. PCCI combustion method [3].

PCCI, and RCCI are shown in Table 1.

Figure 2. Combustion control strategies (a) compression ignition (CI), (b) spark ignition (SI), and (c) homogeneous charge compression ignition (HCCI). Source: http://crf.sandia.gov/combustion-research-facility/engine-combustion/fuels/.

temperature, pressure, and mixture composition inside the combustion chamber. In its development, HCCI was limited by the narrow operating range and the unpredictable combustion delay and behavior. The maximum pressure generated was very high but produced a low mean effective pressure due to the short combustion duration. Many methods and possibilities were proposed to control HCCI engines. In this process, the paradigm of creating an autoignition process from homogeneous charge is shifting to the method of controlling autoignition. The first development is the premixed charge compression ignition (PCCI). This concept was introduced by Aoyama et al. [1]. Gasoline was subjected into diesel-like environment with high compression ratio 17.4:1. A port injection method was used to create the premixed charge in the combustion chamber where the fuel is injected very close to the intake valve closing time as shown in Figure 3.

The combination starts with gasoline and diesel as the low-reactive fuel and high-reactive fuel, respectively. It was found that RCCI combustion was able to operate in a wide range of engine loads with near-zero NOx and soot emissions, accepted pressure rise rate and high indicated efficiency. However, RCCI still could not achieve high load operation with power outputs comparable to CI engine. The combustion behavior of RCCI is somewhat still unpredictable. Further investigation on the important parameters in RCCI combustion control will improve the understanding of the combustion process of RCCI that leads to better control of the process and better engine output.

The premixed charge compression ignition (PCCI), reactivity charge compression ignition (RCCI), and spark-assisted HCCI are some of the established methods of controlling the autoignition process in an engine. All of these methods are categorized as CAI engines. Regardless of the limitations of the controlled autoignition (CAI)-based combustion system, CAI offers high efficiency [4], low fuel consumption [5], and low emission [6], which are the main aims of future engine development. The attributes that differentiate SI, CI, HCCI, PCCI, and RCCI are shown in Table 1.

These earlier works are the basis of the controlled autoignition engine concept. The primary focus of the CAI combustion concepts is identifying the relevant influencing parameters as well as control parameters of this system to widen the operating range and improve the efficiencies. The need for a thorough understanding of the CAI combustion process initiates further discussion on the method to control its combustion. The next stage is to determine the engine parameters that have a direct effect on the combustion. As these steps are carefully defined, high efficiency, low fuel consumption, and low emissions internal combustion engines are achievable (Table 2).

Figure 3. PCCI combustion method [3].

temperature, pressure, and mixture composition inside the combustion chamber. In its development, HCCI was limited by the narrow operating range and the unpredictable combustion delay and behavior. The maximum pressure generated was very high but produced a low mean

Figure 2. Combustion control strategies (a) compression ignition (CI), (b) spark ignition (SI), and (c) homogeneous charge compression ignition (HCCI). Source: http://crf.sandia.gov/combustion-research-facility/engine-combustion/fuels/.

54 Improvement Trends for Internal Combustion Engines

Many researches have been done in the effort of controlling CAI combustion-based system. Agarwal et al. [7] summarize the various types of combustion method and some method in controlling the combustion process. There are various areas that require improvement in order to reshape the combustion and improve the efficiency while still having a low emission. Development of control on ignition timing [8], method in slowing down the heat release rate at high load [9, 10] and development of intake and exhaust manifold for multicylinder engine are among the few area of improvement that have been identified in the area of CAI combustion system. Focusing on the RCCI combustion control method, Li et al. [11] categorized the control by two main categories, fuel and engine management. The fuel management includes two fuel strategies [12, 13] and single fuel strategy with additives, while the engine management

include fuel ratio [14], injection strategy [15–18], EGR rate [19], compression ratio [16], bowl

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This chapter introduces two low reactive fuels, gasoline and CNG, in an RCCI combustion system in order to increase the limit of RCCI engine operation. It introduces a method that has different principals compared to RCCI by introducing combination of low reactive fuels rather than combination of high- and low-reactive fuel. Furthermore, this chapter also introduces the method of RCCI combustion control by varying the stratification by varying the injection timing and gap between two fuel injectors. Two approaches were done to investigate the behavior of gasoline-CNG mixtures in the RCCI combustion system. First approach is experimental testing on a single cylinder engine that was converted to dual fuel engine with gasoline injected at intake port, while CNG is directly injected into the combustion chamber. The stratification was done by

The second approach is the combustion testing in a constant volume chamber with both fuels that are directly injected into the combustion chamber. In this setup, the stratifications level in

The test procedure and equipment used in both approaches are elaborated in this section.

The engine used for this experimental study houses the fuel system of direct injection of gaseous fuel and has compression ratio of 14. This engine is a single cylinder water-cooled engine coupled to an electric dynamometer that can be used for starting the engine and measuring the brake torque produced by the engine. Figure 4 shows a schematic drawing of the engine.

An electric heater is provided to heat the lubricant oil to help warm up the engine faster. A separate control unit controls the operation of the pumps and the temperature of the oil and water by temperature controllers. The control unit also controls the operation of the dynamometer, which also serves as the starter motor and the engine can be motored at a wide range of speeds. There are standard features of safety included in the control unit such as emergency switch, automatic shut down upon the excessive rise in the oil and/or coolant temperatures, or

A commercially available gasoline port fuel injector was used and its specifications can be found in Table 3. This injector has low flow rates and was selected to match the requirement of injecting very low quantities of gasoline to operate in HCCI mode with ultralean mixtures. The injector comes calibrated in the factory to inject and precisely meter the volume against the

geometry [20, 21], stability control, and utilization of two injectors.

varying the injection timing of CNG, while gasoline is kept homogeneous.

chamber is done with varying the injection gap between two fuel injections.

any abnormal conditions of electrical power supply (Figure 5).

2. Test procedure and equipment

2.1. Engine testing and equipment

specified injection duration.


Table 1. Traditional and the controlled autoignition (CAI)-based combustion mode.


Table 2. Summary of specifications of the engine.

include fuel ratio [14], injection strategy [15–18], EGR rate [19], compression ratio [16], bowl geometry [20, 21], stability control, and utilization of two injectors.

This chapter introduces two low reactive fuels, gasoline and CNG, in an RCCI combustion system in order to increase the limit of RCCI engine operation. It introduces a method that has different principals compared to RCCI by introducing combination of low reactive fuels rather than combination of high- and low-reactive fuel. Furthermore, this chapter also introduces the method of RCCI combustion control by varying the stratification by varying the injection timing and gap between two fuel injectors. Two approaches were done to investigate the behavior of gasoline-CNG mixtures in the RCCI combustion system. First approach is experimental testing on a single cylinder engine that was converted to dual fuel engine with gasoline injected at intake port, while CNG is directly injected into the combustion chamber. The stratification was done by varying the injection timing of CNG, while gasoline is kept homogeneous.

The second approach is the combustion testing in a constant volume chamber with both fuels that are directly injected into the combustion chamber. In this setup, the stratifications level in chamber is done with varying the injection gap between two fuel injections.
