Premixed Charge Compression Ignition Combustion Research Articles

A Simulation Study on a Premixed-charge Compression Ignition Mode-based Engine Using a Blend of Biodiesel/Diesel Fuel under a Split Injection Strategy

Environmental pollution from transportation means and natural resource degradation are the top concern globally. According to statistics, NOx and PM emissions from vehicles account for 70% of total emissions in urban areas. Therefore, finding solutions to reduce NOx and PM emissions is necessary. Changing the engine's internal combustion method is considered promising and influential among the known solutions. One of the research directions is a combustion engine using the Premixed Charge Compression Ignition (PCCI) method combined with biofuels to improve the mixture formation and combustion process, reducing NOx and PM emissions. Therefore, this study presents the mechanism of the formation of PM and NOx emissions in the traditional combustion and the low-temperature combustion process of internal combustion engines. Besides, the theoretical basis of flame spread during combustion is also introduced. The key feature of this research is that it has modeled the combustion process in diesel engines under the PCCI modes. This was accomplished using blends of waste cooking oil (WCO)-based biodiesel and diesel fuel, as well as the ANSYS Fluent software. The results showed that PCCI combustion using B20 fuel can significantly reduce NOx and PM emissions, although HC and CO emissions tend to increase, and thermal efficiency tends to decrease. In further studies, different modes of the PCCI combustion process should be thoroughly examined so that this process can be implemented in practice to reduce pollutant emissions.

Combustion noise characterization and optimization of PCCI combustion using response surface methodology

The current work aims at characterizing the premixed charge compression ignition (PCCI) combustion with regression-based approach using response surface methodology. PCCI operating parameters such as load, pilot injection timing, main injection timing, pilot injection quantity, exhaust gas recirculation and injection pressure are considered as input variables. Engine performance indicators such as brake thermal efficiency, brake specific fuel consumption, carbon monoxide (CO), hydrocarbon (HC), oxide of nitrogen (NOx), smoke emissions, combustion phasing and combustion noise metric ringing intensity are considered as output responses. Experimental results validate the optimal solution from response surface methodology approach, and good agreement is found between mathematical models and experimental results. Comparative examination of optimized PCCI combustion versus conventional combustion showed a 66% and 44% decrement in NOx and smoke emissions. Except for CO and HC emissions, the percentage penalty of other responses with PCCI combustion is less than 10%. In addition to ringing intensity another combustion noise metric combustion noise level is computed from Fast Fourier Transform (FFT) analysis of cylinder pressure trace. A combustion noise level of 73.26 dB is obtained at optimized conditions.

Effect of early intake valve closing, exhaust gas recirculation and split injection on combustion and emissions characteristics of a HDDI diesel engine operating in PCCI combustion mode

Premixed Charge Compression Ignition (PCCI) combustion is an alternative to conventional diffusion-controlled combustion for Mono-nitrogen oxides (NOx) and soot emissions reduction in DI diesel engines. However, bringing the center of combustion (CoC) near top dead center (TDC) to reduce brake specific fuel consumption is challenging. In this study, for two Early Intake Valve Closing (EIVC) profiles of split injection strategy, combustion characteristics and emissions of a heavy-duty direct injection (HDDI) diesel engine are evaluated by CFD simulations. Combustion efficiency, Indicated Specific Fuel Consumption (ISFC), NOx, soot, and carbon monoxide (CO) emissions are evaluated for 40 ˚CA and 80˚CA EIVC timings with respect to the base diesel combustion with 0, 30, 50, and 70% Exhaust Gas Recirculation (EGR) rates at 3 bar Brake Mean Effective Pressure (BMEP).CFD simulations reveal that EIVC strategy can displace the CoC towards TDC up to 5–10 ˚CA depending on the EGR rate. Moreover, up to 30% NOx reduction can be achieved in EIVC cases. In 70% EGR case, lower ISFC and near zero NOx emissions can be obtained compared to conventional diesel combustion due to CoC being closer to TDC. However, the EIVC strategy with EGR increases CO emissions due to incomplete combustion of a lower air/fuel ratio mixture.

A new concept for high efficiency and clean diesel combustion by controlling mixture distribution with dual zone combustion chamber

While various measures are being promoted globally toward carbon-neutrality, internal combustion engines are required to achieve a further improvement in thermal efficiency in order to generate less CO2. For diesel engines, premixed charge compression ignition (PCI) combustion has been proposed as a combustion method that can achieve high thermal efficiency and clean emissions simultaneously. However, the application of PCI combustion remains limited to the light load range of certain mass-produced engines as it is difficult to control ignition timing and combustion noise. In this study, we developed a new combustion concept, Distribution Controlled partially Premixed Compression Ignition (DCPCI), which enables partially premixed combustion in medium load ranges by spatially controlling fuel mixture distribution. With this DCPCI combustion, we aim for highly efficient and clean combustion by suppressing the interference between the burned gas produced by the earlier stage injection and the subsequent spray with the use of a dual-zone combustion chamber and multi-stage injection. The effectiveness of the new combustion concept was validated by Computational Fluid Dynamics (CFD) analyses, and the improvement in thermal efficiency was confirmed by engine experiments.

A CFD Study on the Effects of Injection Timing and Spray Inclusion Angle on Performance and Emission Characteristics of a DI Diesel Engine Operating in Diffusion-Controlled and PCCI Modes of Combustion

In three-dimensional (3D) computational fluid dynamics (CFD) simulations, the effects of injection timing and spray inclusion angle (SIA) on performance and emissions of diffusion-controlled and Premixed Charge Compression Ignition (PCCI) combustion in part load for a heavy-duty direct injection (HDDI) diesel engine are studied. The start of injection (SOI) of a 146° SIA injector is varied between −70 and −10 °crank angle (°CA) after top dead center (ATDC). For −50 °CA ATDC SOI with various SIAs between 80° and 146°, PCCI combustion reduces mono-nitrogen oxide (NOx) emissions significantly compared to conventional diesel combustion (CDC). Due to incomplete combustion in rich zones formed by droplet–cylinder wall interaction, early wide SIA injection deteriorates combustion efficiency (CE) and Indicated Mean Effective Pressure (IMEP) and increases soot and carbon monoxide (CO) emissions. Narrow-angle sprays interacting with the piston bowl elevate CE and IMEP and decrease soot and CO emissions but increases NOx emissions. Optimal combustion is achieved by avoiding fuel droplet–cylinder wall interaction. By spray-targeting at the stepped lip of the piston bowl, 100° SIA and −50 °CA ATDC SOI yield, respectively, the highest CE and IMEP: 97.8% and 3.37 bar and the lowest soot and CO emissions: 33.5 and 2.2 ppm, with acceptable NOx emissions.

Effect of injection strategy optimization on PCCI combustion and emissions under engine speed extension in a heavy-duty diesel engine

To mitigate the consequent emissions of greenhouse gases and to conform to increasingly strict vehicle emission requirements, experiments and numerical simulation were used to study effects of multiple injection strategy on premixed charge compression ignition (PCCI) combustion and emissions under speed extension in a heavy-duty diesel engine fueled with diesel. As the speed increases, the injection duration is prolonged, the injection rate is decreased, the fuel-oxygen mixing degree is decreased. In order to enhance fuel-oxygen mixing, the injection timing of single injection should firstly be optimized to fully utilize the shape of the chamber. Compared with single injection, the double injections can increase the mixing time, the optimized multiple injections can further increase the mixing time, making the premixing more sufficient and the combustion more complete. Compared with double injections, the optimized multiple injection strategy used in this paper adds a short pulse pilot injection before the main injection, which prolongs the duration of turbulent motion in the cylinder, and enhances the mixing rate of the main injection fuel and air. Results reveals that for single injection with injection timing of −15°CA ATDC, at low speed, through optimizing the injection strategy, the NOx and soot emissions are reduced by 38.5% and one order of magnitude, respectively, and the gross indicated thermal efficiency (ITEg) is increased by 8.66%; at medium speed, by optimizing the injection strategy, the NOx and soot emissions are reduced by 59.3% and 70.4%, respectively, and the ITEg is increased slightly by 0.33%; at high speed, by optimizing the injection strategy, the soot emission is decreased significantly, the NOx emissions and the ITEg are increased slightly. It was found that with the increase of speed, the effect of multiple injection strategy on the ITEg and emissions is gradually increased, and the optimization effect of multiple injection strategy is more obvious than that of low speed.

Influence of different biodiesel fuels on the PCCI-DI combustion concept for constant speed genset application

Homogenous charge compression ignition (HCCI) is a technology for concurrently reducing nitrogen oxides (NOx) and particulate matters (PM) emissions. Since, the pure HCCI lags in control over combustion phasing, Pre-mixed charge compression ignition (PCCI) method is proposed. To achieve partial homogeneity in PCCI combustion, the air is pre-injected with fuel. The main injection is required for the combination to take place. This paper investigates the impact of using the varying percentages and types of bio-diesels for the constant speed genset application engine. The paper first discus the effect of various ratios of diesel and biodiesel mixtures on the performance parameters like engine power, specific fuel consumption (sfc) and the break thermal efficiency. These effects are caused by the combustion happening inside the combustion chamber which can be seen in pressure, temperature and heat release curves. The result of the simulation finally discusses the formation of NOx and PM emissions during the combustion. These results also provide guidelines for actual testing of the engine with bio-diesel.

Computational study of the Premixed Charge Compression Ignition combustion in a Rapid Compression Expansion Machine: Impact of multiple injection strategy on mixing, ignition and combustion processes

Combustion processes operating under the low-temperature (LTC) are a promising alternative for internal combustion engines, achieving high efficiency and low emissions within the legislative framework. Under this field of study, the concept of Premixed Charge Compression Ignition (PCCI) was introduced to control the combustion phase by varying the injection strategy. The present research, based on the aforementioned combustion strategy, employs Computational Fluid Dynamics (CFD) to study the mixing, ignition and initial combustion processes in a Rapid Compression and Expansion Machine (RCEM). The operating conditions of the PCCI strategy are achieved through the split injection technique, which separate the injection into several shots. In this case, the injection strategy consists of a long base injection and two very short, consecutive post injections delivered when the piston is close to the top dead center. Three different operating conditions have been considered which differ mainly in the duration and the starting time of the first injection. Large Eddy Simulations (LES) are selected to account for the effects of turbulence. Results are validated against experimental data, showing good agreement between both approaches. The effect of the first injection on the second one in multiple injection strategy is appreciated as the penetration of the subsequent fuel sprays is faster. Differences in the local mixture field and ignition dynamics are observed as a function of varying operating conditions. The ignition process is highly influenced by the operating strategies affecting the distribution of the mixture and thus the location of the low temperature oxidation. In the current computational study, in addition to the evaporating fuel scalar, the corresponding source term due to evaporation has also been provided to three passive transported scalars, namely three mixture fractions, one for each injection event. This allows for discerning the fuel stemming from each one of the pulses in the overall distribution, thus offering new insights into the effect of the injection strategy.

Multiple fuel injection strategy for premixed charge compression ignition combustion engine using biodiesel blends

In the last decade, advanced combustion techniques of the low-temperature combustion (LTC) family have attracted researchers because of their excellent emission characteristics; however, combustion control remains the main issue for the LTC modes. The objective of this study was to explore premixed charge compression ignition (PCCI) combustion mode using a double pilot injection (DPI; pilot-pilot-main) strategy to achieve superior combustion control and to tackle the soot-oxides of nitrogen (NOx) trade-off. Experiments were carried out in a single-cylinder research engine fueled with 20% v/v biodiesel blended with mineral diesel (B20) and 40% v/v biodiesel blended with mineral diesel (B40) vis-à-vis baseline mineral diesel. Engine speed and rate of fuel-mass injected were maintained constant at 1500 rpm and 0.6 kg/h mineral diesel equivalent, respectively. Pilot injection timings (at 45° and 35° before top dead center (bTDC)) and fuel quantities were fixed, while three fuel injection pressures (FIPs) and four different start of the main injection (SoMI) timings were investigated in this study. Results showed that multiple pilot injections resulted in a stable PCCI combustion mode, making it suitable for higher engine loads. For all test fuels, advancing SoMI timings led to relatively lesser knocking; however, engine performance characteristics degraded at advanced SoMI timings. B40 exhibited relatively superior engine performance among different test fuels at lower FIP; however, the difference in engine performance was insignificant at higher FIPs. Fuel injection parameters showed a significant effect on emissions, especially on the NOx and particulates. Advancing SoMI timing resulted in 20%–50% lower particulates emissions with a slight NOx increase; however, the differences in emissions at different SoMI timings reduced at higher FIPs. Somewhat higher particulates from biodiesel blends were a critical observation of this study, which was more dominant at advanced SoMI timings. Qualitative correlation between NOx-total particulate mass (TPM) was another critical analysis, which exhibited the relative importance of different fuel injection parameters for other alternative fuels. Overall, B20 at 700 bar FIP and 20° SoMI timing emerged as the most promising proposition with some penalty in CO emission.

Effects of pilot injection strategy on in-cylinder combustion and emission characteristics of PODE/methanol blends

Polyoxymethylene dimethyl ethers (PODE) and methanol are both promising alternative fuels with high oxygen content, and the combustion and emission characteristics of PODE/methanol blends were investigated in a common-rail engine. The premixed charge compression ignition (PCCI) combustion was realized by appropriate match of main injection and pilot injection strategies. The effects of methanol ratio (0– 20%) on fuel economy and emissions formation were studied in conventional compression ignition (CI) and PCCI modes. The combustion and emission characteristics were improved by adjusting the pilot injection timing (−40 ~ −24 °CA ATDC) and pilot injection ratio (0– 20%). The results show that the increase of methanol ratio prolongs the ignition duration, increases the premixed combustion ratio and reduces NOx emissions. PCCI combustion increases the brake thermal efficiency (BTE) and improves the trade-off relationship between NOx and soot. The delay of pilot injection timing increases the BTE, decreases HC, CO and HCHO emissions, but increases NOx and soot emissions. The appropriate pilot injection ratio can significantly increase the BTE, and has little effect on the emission characteristics. Under the optimized pilot injection strategy and appropriate methanol ratio conditions, the maximum BTE of the blends can reach 46.58% and maintain low emission level.

Effects of speed extension on PCCI combustion and emissions in a heavy-duty diesel engine at medium load

Effects of boost pressure, engine speed and multi-pulse injection timing on premixed charge compression ignition (PCCI) combustion and emissions in a heavy-duty diesel engine at medium load were studied experimentally and numerically. Results show that, intake boost makes the high temperature ignition timing advance, but the mass fraction of lean mixture increases dramatically and the mass fractions of rich and over-rich mixtures decrease significantly, indicating that intake boost helps the formation of lean and homogeneous mixture; the indicated thermal efficiency increases and the combustion loss decreases. When the engine speed is increased with other variables constant, the high temperature ignition timing is retarded, the mass fraction of over-rich mixture decreases; the NOx, soot, CO and UHC emissions are all decreased; the indicated thermal efficiency increases, the combustion loss decreases, but the exhaust loss increases. The delay of multi-pulse fuel injection timing with other variables constant shortens the mixing time, increases the mass fraction of over-rich mixture, and increases the initial soot generation. However, due to the combined effect of mixing space and combustion temperature, the final soot, CO and UHC emissions are all decreased, and the NOx emissions have little change; the indicated thermal efficiency increases, the combustion loss decreases, but the exhaust loss increases.

Study on Design Method of Combustion Reference Values for Model-Based Control of Advanced Diesel Engine

Abstract Model-based control systems are drawing attention in relation to implementing advanced combustion technologies with high thermal efficiency and low emissions, such as homogeneous charge compression ignition and premixed charge compression ignition combustion, having low robustness. A model-based control system for engine combustion derives control inputs based on reference values and operating conditions in each cycle. Thus, it can replace the conventional control map, which necessitates a significant number of experiments. However, model-based control for combustion requires reference values, such as heat-release-rate peak timing and value, which represent the combustion state. In addition, because model-based control systems derive control inputs cycle by cycle, the combustion reference for the transient condition is critical for maximizing the benefit of such systems. Therefore, this study describes a design method of the combustion reference values for transient operation. The combustion method targeted in this study is a premixed compression ignition combustion that exhibits two-stage heat releases and can reduce combustion noise. Particularly, a method using predicted future operating conditions considering the driving characteristics is proposed. Designed combustion reference values with the proposed method were evaluated with engine control experiments in a certain part of worldwide harmonized light vehicles test cycle. Results indicate that the rate of achieving the desired two-stage heat releases combustion improved from 57% to 81% and combustion noise reduced. Thus, designing the combustion reference values for transient operation by considering future operating conditions is effective to ensure advanced combustion. In addition, such a method can consider the driving characteristics.

Exploring the Possibility of Achieving Partially Premixed Charge Compression Ignition Combustion of Biodiesel in Comparison to Ultra Low Sulfur Diesel on a High Compression Ratio Engine

ABSTRACT The combustion characteristics of biodiesel operating in the Low Temperature Combustion (LTC) regime, via Partially Premixed Charge Compression Ignition Combustion (PPCI), is relatively unknown. Therefore, this study compares engine performance and emissions of ultra-low sulfur diesel (ULSD) and waste cooking oil biodiesel through an attempted PPCI methodology. The Fuel Injection Timing (FIT) was gradually altered from conventional combustion timing (12.0° for biodiesel and 12.5° for ULSD) to 35.0° before top dead center. Results indicated that the fuel consumed to maintain the required load condition increased gradually for both ULSD and biodiesel due to the start of combustion shifting further into the compression stroke for each injection advancement. Nitrogen oxides (NOx), particulate matter (PM), carbon monoxide, and total hydrocarbons were marginally lower for biodiesel compared to ULSD. There was limited success in reducing both NOx and PM emissions simultaneously by varying the FIT alone for both fuels. The high compression ratio of the engine utilized was a major limiting factor in achieving LTC. Importantly, the Negative Temperature Coefficient (NTC) behavior of biodiesel and its impact on ignition delay was successfully captured. The operating conditions used in this study are closer to a production engine as compared to shock tube and constant volume combustion systems typically used to validate chemical kinetic (CK) models. Moreover, data surrounding NTC and its influence on ignition delay with biodiesel in CI engines is limited in the literature. Thus, the results presented provide valuable data that could be utilized to help validate CK models investigating the behavior of biodiesel fuels.

Particulate characteristics of low-temperature combustion (PCCI and RCCI) strategies in single cylinder research engine for developing sustainable and cleaner transportation solution

In this experimental study, particulate matter (PM) characterizations of different low-temperature combustion (LTC) strategies have been compared with conventional compression ignition (CI) combustion for finding out a sustainable and cleaner transport solution. LTC strategies included premixed charge compression ignition (PCCI) and reactivity-controlled compression ignition (RCCI) combustion. Particulate sampling and characterization were carried out in a single-cylinder diesel engine. All engine tests were performed at 1, 2, 3, 4 bar brake mean effective pressure (BMEP) at 1500 rpm. CI and PCCI combustion experiments were performed using mineral diesel as the test fuel. However, mineral diesel and methanol were used as high reactivity fuel (HRF) and low reactivity fuel (LRF), respectively in the RCCI combustion strategy. For all combustion strategies, fuel injection pressure (FIP) was kept constant at 500 bar. However, the number of injections and start of injection (SoI) timings were varied to optimize the engine performance. Results showed that the RCCI combustion strategy emitted a relatively lower concentration of particles than the other two strategies (PCCI and CI). A relatively higher number concentration of accumulation mode particles (AMP) compared to nucleation mode particles (NMP) in the exhaust of the RCCI combustion strategy was an important finding of this study. Number-size and mass-size distributions of particles emitted from different strategies also exhibited the dominant concentration of particles in the CI combustion strategy. PM bound trace metal analysis was yet another critical aspect of this study, which showed that both RCCI and PCCI strategies emitted a relatively lower concentration of trace metals than the conventional CI combustion strategy. Parametric analysis of different PM characteristics and NOx-PM trade-off analysis also demonstrated the importance of LTC strategies over the conventional CI combustion strategy. Overall, this study demonstrated that all LTC strategies could be used for PM and NOx reduction; however, the RCCI combustion strategy was more dominant in NOx and PM reduction, in addition to having an excellent capability of using alternative fuel in the quest for developing sustainable transport solution.

Impact of a split injection strategy on mixing, ignition and combustion behavior in Premixed charge compression ignition combustion

Mixing, ignition and combustion behavior in a rapid compression and expansion machine operated under Premixed Charge Compression Ignition (PCCI) relevant conditions are investigated by combined passive optical and laser-optical high-speed diagnostics. The PCCI concept is realized using a split injection schedule consisting of a long base load injection and two closely separated short injections near top dead center. Previous studies of close-coupled double injections under constant ambient conditions showed an increased penetration rate of the subsequent fuel spray. However, the aerodynamic gain from the preceding injection is counteracted by the density rise during the compression stroke under transient engine conditions. The study confirms that the rate of mixing of the subsequent fuel spray is significantly increased. Regarding combustion behavior, the thermodynamic analysis exhibits contributions of low temperature oxidation reactions of more than 20% to the total heat release, with a notable amount of unburnt fuel mass varying from 25 to 61%. The analysis of the optical data reveals the multi-dimensional impact of changes in operating parameters on the local mixture field and ignition dynamics. The onset of low temperature reactivity of the first short injection is found to be dominated by the operating strategy, while the location is strongly related to the local mixing state. Low temperature ignition of the consecutive fuel spray is significantly promoted, when upstream low temperature reactivity of the preceding injection is sustained. Likewise, it is shown that high temperature ignition is accelerated by the entrainment of persistent upstream low temperature reactivity.

Study on Combustion Processes of a Premixed Charge Compression Ignition (PCCI) Engine Fueled with DME/Diesel

A dimethyl ether (DME) pre-mixing system was installed on a 2105 diesel engine for realizing pre-mixed charge compression ignition combustion mode. Combustion processes of a PCCI engine fueled with DME/diesel under various DME pre-mixing ratios were investigated in this paper. The results showed that the heat release process showed three stages with port induction of DME. As the DME pre-mixing ratio (PR) increased, the peak value of cylinder temperature and pressure raised and the corresponding crank angles advanced. The start of combustion (SOC) moved forward obviously and the duration of combustion extended; the peak value of the pressure rise rate reduced first and then raised. The results in this paper provided a reference for the combustion process optimization of DME/diesel PCCI engine.

Effects of pre-injection strategy on combustion performance of methanol/diesel dual fuel engine at low load

In this paper, the effect of pre-injection timing on the combustion and emission performance of methanol/diesel high premixed charge compression ignition (HPCCI) combustion mode at low load was studied by three-dimensional numerical simulation. The simulation is carried out under the conditions of 1900 r/min and 25% load, and the pre-injection diesel mass remains constant and the pre-injection timing is changed under the conditions of 50% and 60% methanol ratio respectively. The results show that with the delay of pre-injection timing, the evaporation of pre-injected fuel in cylinder becomes faster, the low temperature reaction is enhanced, and the peak value of heat release rate is higher. In addition, the distribution of pre-injected diesel in cylinder and the position of impact wall are the important factors affecting the combustion and emission performance in cylinder, and when the injection timing is -35 °CA ATDC, the combustion and emission characteristics of the engine are optimal. Finally, by comparing with the traditional RCCI combustion mode, the enhancement ability of HPCCI combustion mode on methanol combustion efficiency under low load is verified and analyzed.

Numerical study of the effects of split injection strategy and swirl ratio for biodiesel PCCI combustion and emissions

New methods have been studied in the past few decades to decrease exhaust emissions and fuel consumption of diesel engines. Using new combustion methods as low-temperature combustion (LTC) strategies and also utilizing new fuels as bio-diesel are beneficial ways to overcome diesel engine issues. This numerical study focused on the effect of split injection strategies as well as swirl ratio (SR) on the biodiesel premixed charge compression ignition (PCCI) combustion process and the related emissions. In this regard, KIVA-3V code as a CFD tool has been utilized to analyze the combustion and emission characteristics of the diesel engine. Single and split injection strategies have been executed on biodiesel PCCI combustion and have been compared in order to probe and examine the injection strategies. The results show that in both strategies, advancing the injection timing can lower the combustion emission and improve the engine performance by optimizing the start of injection (SOI) as sweet spot value. Utilizing a high swirl ratio with the split injection strategy has a negative effect on overall combustion, emission, and performance in comparison with the single injection strategy. For multi-injection scheme, SOI = −35 ATDC, SR = 1.1, and for single injection scheme, SOI = −40 ATDC, SR = 1.1 are considered as optimum cases regarding minimum total exhaust emissions and highest performance.

Effects of External Mixture Formation and EGR Technique on a Diesel-Fueled PCCI Engine

Limitations on exhaust emissions of diesel engines have become increasingly stringent due to increasing awareness of environmental protection. This challenges diesel engine manufacturers to find a new balance between engine performance and emissions. Advanced combustion modes for diesel engines, such as homogeneous charge compression ignition (HCCI) and premixed charge compression ignition (PCCI), which can simultaneously reduce exhaust emissions and substantially improve thermal efficiency, have drawn increasing attention. In order to allow enough time to prepare the homogeneous mixture, the external mixture formation technique was used to achieve PCCI combustion. A device known as diesel vaporizer was used to produce diesel vapors. Diesel vapors mix with air at intake port of an engine to form homogeneous charge before combustion starts. Exhaust gas recirculation technique was used to control early ignition of the premixed charge. It was observed from the experimentations that the use of external mixture formation technique with EGR in PCCI engine decreases the NOx emissions by 43.57% but increases HC and CO emissions due to low temperature combustion. The brake thermal efficiency obtained was just 1.9% less than the conventional CI engine.

The potential of heat release rate and cylinder pressure feedback control for conventional and premixed charge compression ignition combustion

Cylinder pressure or heat release rate tracking algorithms for direct-injected compression ignition engines allow to account for various disturbances, such as changes in the fuel characteristics or the effects of engine wear. They are suited for flex-fuel engines and allow the use of multi-injection strategies; hence, they show potential for mobile applications. However, they are based on the assumption that the heat release rate or cylinder pressure correlates well with engine efficiency and emissions and therefore allows a clean and efficient engine operation. With the objective to evaluate the potential of such tracking algorithms, this assumption is investigated for conventional as well as for low-temperature combustion strategies with diesel as fuel of choice. Based on experimental data, exploratory data analysis methods are applied to evaluate how sensitive engine efficiency and emissions are to changes of the heat release rate or cylinder pressure. Furthermore, an extended tracking algorithm is proposed, which can be applied for premixed charge compression ignition combustion concepts.