Cylinder Pressure Variation Research Articles

A comparative study on combustion characteristics of PPC and RCCI combustion modes in an optical engine with renewable fuels

Application of renewable fuels in compression ignition engines provides one solution to reduce greenhouse gas emission in heavy-duty transportation sector. However, it is a big challenge to find a single alternative fuel to replace the traditional diesel under full load conditions. In this study, the combustion characteristics of two kinds of renewable fuels with different reactivity, namely methanol and hydrogenated catalytic biodiesel (HCB), were investigated in an optical engine under partially premixed combustion (PPC) and reactivity-controlled compression ignition (RCCI) modes, respectively. A two-color (2C) method was employed to quantify the in-flame soot formation. Meanwhile, the flame oscillation phenomenon was captured and evaluated. The results indicate that the RCCI mode exhibits reduced peak cylinder pressure, resulting in smoother and more stable combustion compared to that of the PPC mode. Moreover, the more uniform fuel distribution in the RCCI mode further decreases soot formation from the blended fuel. Additionally, with increasing methanol proportion, the rise in oxygen content within the blended fuel significantly reduces soot formation. The flame oscillations are primarily related to the rate of cylinder pressure variation. Under PPC mode, multi-point autoignition causes a rapid increase in cylinder pressure, leading to larger oscillation amplitudes (M15: 0.268, M25: 0.772). Conversely, under the RCCI mode, the heat release process is more stable, resulting in weaken oscillations (M15: 0.161, M25: 0.064) compared to that of PPC.

Coupling effect of shaft torsional vibration and advanced injection angle on medium-speed diesel engine block vibration

Engine body vibration is an important safety concern for diesel engines as it can lead to severe engine damages and even catastrophic failures. Traditional methods for excitation computation assume that the rotational speed and the cylinder pressure remain stable under each working cycle, which makes it impossible to precisely predict vibration peaks at certain frequencies. But in practice, the existence of shafting torsional vibration will lead to the fluctuation of rotational speed and cylinder pressure. To predict engine block vibration more accurately, this paper proposes a novel method considering the instantaneous variations in rotational speed and cylinder pressure. It is implemented by two steps. Firstly, an innovative model considering the coupling effect between shaft torsional vibration and advanced injection angle is proposed, it particularly explains how the cylinder pressure and instantaneous rotational speed vary due to the coupling effects. Secondly, the excitation forces that cause block vibration are analyzed and their computational formulas are improved. This method also considers the offset of excitation loading position caused by torsional vibration. The coupling model is experimentally verified and the excitations are loaded into a finite element model of the diesel engine for vibration response prediction. The results reveal that the coupled model can predict vibration peaks at sideband frequencies and thus makes the frequency spectrum much richer than that of the traditional method. Furthermore, it shows that the acceleration results obtained by the coupled model have better prediction accuracy than those obtained from traditional methods, with the deviation percentage reducing from 6.31% and 8.41% to 0.64% and 0.32% in the X and Z direction. It indicates that the coupled model is more reliable in predicting the vibration response of the engine block. Finally, the effect of advanced injection angle on engine block vibration is investigated and the optimal value of the advanced injection angle is determined to be 29 CA, which makes the engine block vibration reduced by 3.60%, 2.72%, and 3.16% in the X, Y, and Z direction comparing to the original advanced injection angle. Overall, this study presents an improved approach for predicting engine block vibrations and offers valuable insights for the design of shafting structures and fuel injection parameters in marine diesel engines.

Effects of Engine Load and Ternary Mixture on Combustion and Emissions from a Diesel Engine Using Later Injection Timing

As a high oxygenated fuel, bioethanol has already obtained more and more widespread attention in diesel engines. The present work aims to study and compare effects of various diesel-bioethanol-biodiesel ternary mixture fuels on combustion and emissions from a four-cylinder diesel engine. A series of engine experiments are conducted on neat diesel fuel (D100), 95% D100 blended with 5% bioethanol and 1% biodiesel by volume (D95E5B1), 90% D100 blended with 10% bioethanol and 1% biodiesel by volume (D90E10B1), and 85% D100 blended with 15% bioethanol and 1% biodiesel by volume (D85E15B1) according to various engine loads (40, 80 and 120 Nm). The experimental results show that the peak value of pressure and heat release rate (HRR) in the cylinder, nitrogen oxides (NOx) and smoke emissions increase with the increase in engine load, but the brake specific fuel consumption (BSFC) decreases. There is no significant variation in cylinder pressure with the addition of ethanol, but HRR is improved and NOx and smoke emissions are effectively controlled. It is exciting that the addition of ethanol can simultaneously reduce NOx and smoke emissions under medium and high load conditions. Specifically, at 120 Nm, ethanol addition simultaneously reduces NOx emissions by 2.08% and smoke opacity by 36.08% on average. Through the results of this study, it is found that the ethanol can improve the combustion of the four-cylinder diesel engine and also effectively control the emissions of NOx and smoke. Therefore, ethanol will play an important role in the future research field of energy saving and emission reduction for diesel engines.

Experimental Determination of Suitability of Algae Bio Diesel Blend as an Alternate to Diesel Fuel using Cylinder Pressure Variation with Respect to Crank Angle

Scientific and engineering community of whole world is working day and night to develop an alternate of fossil fuel. This is not only due to continuous depletion of fossil fuel reserves but also for day by day increasing global warming. This global warming is mainly due to emission of harmful gases from manufacturing industries and vehicles used for transportation including aerial vehicles. In this paper, an experimental study has been performed in variation of mean cylinder pressure at crank angles divided into 4 categories for each stroke. 180 actual movement of crankshaft is taken as 90 for study. Further analysis is done for all the four strokes starting from power stroke at 0 and end of compression stroke as 360 (actually 720). The fuel used for the study is a 20% blend of biodiesel named as B20 in the paper. The experimental results obtained in a variable compression ratio engine are compared with the corresponding characteristics of fossil fuel. Diesel named as D100 which is a proved and widely used fuel at present. The comparative study has shown a clear indication that though biodiesel blend B100 may not be suitable in, as it’s condition but blend B20 may be suitable to be used in as is condition as the experimental results are not varying largely with that of pure diesel. Variation in power strokes and exhaust strokes were found to have larger deviation from linear trend whereas it followed linear variation in induction and compression stroke. The performance can be improved further by using suitable additive in further research works.

In-cylinder pressure based combustion analysis of cycle-by-cycle variations in a dual spark plug SI engine using ethanol-gasoline blends as a fuel

The combustion in Spark Ignition (SI) engine varies from the engine working cycle-by-cycle the ability to predict accurately the pressure allows for a better understanding of the processes that take place in the cylinder The effects of load, compression ratio, and ethanol content on the cycle-by-cycle cylinder pressure variations of a dual spark plug gasoline engine have been investigated experimentally. Cycle-by-cycle cylinder pressure variations were evaluated using coefficient of variation (COV) of maximum cylinder pressure. The results showed that the maximum cylinder pressure increased and corresponding its cycle-by-cycle variations decreased with the increase of load, compression ratio and ethanol content in the blend. Greater variations were observed at lower loads than full load operation of the engine. Highest maximum cylinder pressure and lowest it’s COV were achieved for 20% ethanol by volume in the blend under full load at compression ratio of 10:1. The maximum cylinder pressure crank angle was moved closer to the top dead center as the ethanol fraction in the blend increased. Finally, it can be concluded that the addition of ethanol 20% by volume to the gasoline maintains COV of maximum cylinder pressure at a low level.

Effects of Water Injection Strategies on Oxy-Fuel Combustion Characteristics of a Dual-Injection Spark Ignition Engine

Currently, global warming has been a serious issue, which is closely related to anthropogenic emission of Greenhouse Gas (GHG) in the atmosphere, particularly Carbon Dioxide (CO2). To help achieve carbon neutrality by decreasing CO2 emissions, Oxy-Fuel Combustion (OFC) technology is becoming a hot topic in recent years. However, few findings have been reported about the implementation of OFC in dual-injection Spark Ignition (SI) engines. This work numerically explores the effects of Water Injection (WI) strategies on OFC characteristics in a practical dual-injection engine, including GDI (only using GDI), P50-G50 (50% PFI and 50% GDI) and PFI (only using PFI). The findings will help build a conceptual and theoretical foundation for the implementation of OFC technology in dual-injection SI engines, as well as exploring a solution to increase engine efficiency. The results show that compared to Conventional Air Combustion (CAC), there is a significant increase in BSFC under OFC. Ignition delay (θF) is significantly prolonged, and the spark timing is obviously advanced. Combustion duration (θC) of PFI is a bit shorter than that of GDI and P50-G50. There is a small benefit to BSFC under a low water-fuel mass ratio (Rwf). However, with the further increase of Rwf from 0.2 to 0.9, there is an increment of 4.29%, 3.6% and 3.77% in BSFC for GDI, P50-G50 and PFI, respectively. As WI timing (tWI) postpones to around −30 °CA under the conditions of Rwf ≥ 0.8, BSFC has a sharp decrease of more than 6 g/kWh, and this decline is more evident under GDI injection strategy. The variation of maximum cylinder pressure (Pmax) and combustion phasing is less affected by WI temperature (TWI) compared to the effects of Rwf or tWI. BSFC just has a small decline with the increase of TWI from 298 K to 368 K regardless of the injection strategy. Consequently, appropriate WI strategies are beneficial to OFC combustion in a dual-injection SI engine, but the benefit in fuel economy is limited.

Effects of Fischer-Tropsch diesel blending in petrochemical diesel on combustion and emissions of a common-rail diesel engine

Fischer-Tropsch (F-T) diesel fuel from indirect coal-to-liquid (CTL) is a promising alternate fuel for diesel engines. To study the effects of F-T diesel/ petrochemical diesel blends on combustion and emission characteristics under various injection timing (IT) and engine loads, the experiment is conducted on a common-rail diesel engine fueled with pure petrochemical diesel (D100), F-T diesel blended in petrochemical diesel by volume of 30% (D70F30) and 60% (D40F60), respectively. Besides, the combustion stability, including cyclic variation and degree of rough work are compared. The results show that F-T blending fuels always have lower heat release rate (HRR) and pressure rise rate (PRR) than D100 during premixed combustion period, while the differences are not obvious during diffusion combustion period. Additionally, two blends have better ignition property and smaller coefficient of variation of peak cylinder pressure (COVpmax). The rough work has no clear difference for all test fuels at medium–high loads, while the engine has remarkably gentle operation with F-T blending fuels at low and partial loads. Although NOx emissions of two blends are only slight reduced, soot emissions are significantly reduced. So the NOx-soot trade-off can be obviously alleviated.

Investigating the Performance, Reduction of Emission and Combustion Characteristics of YSZ Coated D.I.Diesel Engine Powered by Binary Bio-fuels

Performance, emission and combustion studies were carried out on the ceramic coated diesel engine (YSZ) fed with biodiesel obtained from the oil derived from the mango seeds (MSBD) and MSBD blended with turpentine oil (MSBTO). The performance study showed that the MSBD and MSBTO blends showed 3.6% and 7.1% more BSFC value compared to that of DF in ceramic coated engine due to higher density and viscosity. The maximum brake thermal efficiency was observed 28% for DF in coated engine compared to other fuels due to less fuel consumption of DF because of lower density. The emission characteristics displayed that the MSBTO fuel showed 12%, 15.2% and 29.1% reduction in the smoke density, NOx and CO respectively compared to that of DF in coated engine. However, the MSBD and MSBTO showed 17 and 21% more release of UBHC at full conditions compared to that of DF in ceramic coated engine due to lesser calorific values of MSBD and MSBTO compared to the calorific value of DF. Combustion study revealed that the MSBD and MSBTO displayed less cylinder pressure compared to that of DF in coated engine and the MSBTO fuel showed the 5.3% decrease in the cylinder pressure compared to that of DF in coated engine owing to less heat liberation and lower cetane value. HRR followed the similar trend of variation of cylinder pressure and the MSBTO displayed 7.4% lower HRR compared to that of DF in coated engine.

Experimental Study on Combustion and Performance of a Stationary CIDI Engine Fueled with 1-Heptanol-Diesel Mixtures

1-Heptanol is a renewable higher alcohol for compression ignition direct injection (CIDI) engines because of its distinctive physicochemical properties. The developed renewable production approaches of 1-heptanol promote its application in CIDI engines. The present study investigates the combustion of 1-heptanol/diesel blends with up to 50vol% 1-heptanol substitution ratio on CIDI engine. The substitution ratios of 1-heptanol/diesel are 10/90, 20/80, 30/70, 40/60, and 50/50 (v/v%), denoted as Hep10, Hep20, Hep30, Hep40, and Hep50. This work utilized a one-cylinder natural aspiration air cooling CIDI engine research facility. The steady-state test was performed at various loads ranged between 10% to 100% and engine speeds of 900 and 1500 rpm. The findings reveal that under the same conditions of the TGA experiment, the 1-heptanol/diesel mixture evaporates faster than diesel. 1-Heptanol/diesel mixtures showed longer ignition delay and tend to burn under premixed combustion mode than diesel. Also, Hep10-50 blends released more heat under fast burn mode compared to regular diesel. Hep10-50 mixtures showed higher cyclic variation (COVimep), higher BSFC, lower BTE, lower combustion efficiency, with no significant variations in cylinder pressure, THR, and IMEP compared to regular diesel. Soot and NOx emissions were demoted by 70% and 25% for Hep50 at 100% compared to diesel.

Cyclic Pressure Variations in A Small Diesel Engine Fueled with Biodiesel and Antioxidant Blends

Biodiesel fuel is considered as one of the most competence sustainable replacement for fossil fuel due to their superior combustion characteristics and possesses higher oxygen content. Thus, many researchers recently investigated to improve biodiesel capability by adding additives whether by blending with dual-fuel or tri-fuel. However, the combustion characteristics for biodiesel and biodiesel-additives blends are not thoroughly examined and need additional research works to study how the biodiesel behaviour and characterise. Thus, this research main objective is to study a single-cylinder diesel engine cyclic cylinder pressure variations running with biodiesel with antioxidant (B2HA1.0 and B2HT 1.0) blends with palm oil methyl ester (POME). While The baseline fuels used for this study were biodiesel (B20) and pure diesel (B0). The entire test fuels were examined at a constant engine speed 1800 rpm with 100% engine load condition. The engine combustion characteristics were studied by utilising the indicated mean effective pressure (IMEP) and cyclic variations of combustion pressure at 200 consecutive cycles. Combustion characteristics of engine diesel have been studied by using statistical analysis. The results revealed that the engine running with biodiesel-antioxidants have higher cyclic variations of combustion from B20 and B0, which B2HA1.0 possessed the highest cyclic variations. It can be summarised from the study that biodiesel-antioxidants fuels produce a substantial influence on the engine cyclical variation, which linked to the characteristics of the engine combustion.

Analysis of ignition delay by taking Di-tertiary-butyl peroxide as an additive in a dual fuel diesel engine using hydrogen as a secondary fuel

Ignition delay (ID) is one of the important parameters that make influenced on the combustion process inside the cylinder. This ignition delay affects not only the performances but also the noise and emissions of the engine. In this regards the experiments were conducted on single cylinder 4–stroke compression ignition research diesel engine, power 3.50 kW at constant speed 1500 rpm Kirloskar model TV1 with base fuel as diesel and hydrogen as secondary fuel with and without Di-tertiary-butyl-peroxide (DTBP). Experiments were conducted to measure the ignition delay of the dual fuel diesel (DFD) engine at different load conditions and substitution of diesel by hydrogen with or without DTBP and then it was compared with predicted ID given by Hardenberg-Hase equation and modified Hardenberg-Hase equation.The experimental values of ignition delay were compared with theoretical ignition delay which was predicted on the basis of Hardenberg-Hase equation by considering mean cylinder temperature, pressure, activation energy and cetane number and variations are found in between 6.60% and 21.22%. While, the Hardenberg-Hase equation was modified (by considering variation in activation energy) for DFD engine working on diesel as primary fuel and hydrogen as secondary fuel shows variations 1.20%–11.96%. Furthermore, with DTBP it gives variation up to 18.01%. It was found that ID decreases with increase in percentage of DTBP and hydrogen in air-fuel mixture. This might be due to the cetane improver nature of DTBP, pre-ignition reaction rate and energy release rate of hydrogen fuel. The polytropic index get increased by addition of (Di-tert butyl peroxide) DTBP. Similarly, 5% Di tertiary butyl peroxide reduces Ignition delay.

Analysis of cylinder pressure cyclic variability operating with butanol blends in a diesel engine

Butanol is a second-generation biofuel which obtained from the biomass feedstock sources to improve the fuel properties and performance of the recent fuels. However, there are certain grey aspects in the combustion characteristics of butanol blends in various operating speeds and loads. This work investigates the use of mineral diesel (D), palm biodiesel (B), butanol (10%)-diesel (90%) (DBu10) and butanol (10%)-palm biodiesel (90%) (BBu10) fuels. The objectives of this study are to investigate the cyclic combustion variations of cylinder pressure profiles and peak cylinder pressure, Pmax and analyse the combustion stabilities using recurrence plot (RP) on tested fuels using a diesel engine. The results showed that higher peak cylinder pressures were observed for butanol blends with full load at 1100 rpm. Higher cylinder pressure cyclic variability occurred at high load and speed for all test fuels, especially DBu10 with higher COVPmax values. Thus, in this case, DBu10 produced the most chaotic combustion irregularities and higher cyclic variations for the time series in those conditions. In conclusion, cylinder pressure variations in the time series were found to be affected by the fuel composition of butanol in the blends and types of fuel in engine operation.

Effect of methane augmentation on combustion stability and unregulated emissions in compression ignition engine

The replacement of conventional diesel fuel in CI engines is being attempted by various researchers to solve the problem of the regulated and unregulated engine emissions and diesel scarcity. Additionally, stringent emission norms are motivating to find replacement of diesel with clean and sustainable alternative fuels. In last few decades, the demand of natural gas has increased drastically and it emerged as promising clean and economic energy source for transport. Therefore, the current investigation focuses on methane-diesel dual fuel combustion in single cylinder water cooled diesel engine at rated rpm of 1500. The experiment was performed at different loads (25, 50 and 75%) with varying methane supplementation. The higher methane energy share at lower and higher load conditions were reported as challenging engine operating conditions by various researchers. Therefore, present work explores the effect of higher energy substitution of methane at lower and higher load conditions. At these operating conditions, combustion stability was characterised by coefficient of variation in peak pressure and mean cylinder pressure. The study investigates the combustion stability of methane-diesel dual fuel engine through cycle to cycle variability and peak pressure location variation. Subsequently, the effect of addition of methane were also investigated on unregulated emissions like aldehydes and aromatics, which are reported carcinogens and act as precursors in particulate matter formation. Overall, methane energy share reduces the COV at higher loads and the unregulated emissions at all load conditions.

Engine Performance of a Gardener Compression Ignition Engine using Rapeseed Methyl Esther

This paper presents an experimental investigation on the influence of engine speed on the combustion characteristics of a Gardener compression ignition engine fueled with rapeseed methyl esther (RME). The engine has a maximum power of 14.4 kW and maximum speed of 1500 rpm. The experiment was carried out at speeds of 750 and 1250 rpm under loads of 4, 8, 12, 16 and 18 kg. Variations of cylinder pressure with crank angle degrees and cylinder volume have been examined. It was found that RME demonstrated short ignition delay primarily due to its high cetane number and leaner fuel properties (equivalence ratio (φ) = 0.22 at 4kg). An increase in thermal efficiency but decrease in volumetric efficiency was recorded due to increased brake loads. Variations in fuel mass flow rate, air mass flow rate, exhaust gas temperatures and equivalence ratio with respect to brake mean effective pressure at engine speeds of 750 and 1250 rpm were also demonstrated in this paper. Higher engine speed of 1250 rpm resulted in higher fuel and air mass flow rates, exhaust temperature, brake power and equivalent ratio but lower volumetric efficiency. Keywords— combustion characteristics, engine performance, engine speed, rapeseed methyl Esther

Prediction of Cyclic Variability and Knock-Limited Spark Advance in a Spark-Ignition Engine

Engine knock remains one of the major barriers to further improve the thermal efficiency of spark-ignition (SI) engines. SI engine is usually operated at knock-limited spark advance (KLSA) to achieve possibly maximum efficiency with given engine hardware and fuel properties. Co-optimization of fuels and engines is promising to improve engine efficiency, and predictive computational fluid dynamics (CFD) models can be used to facilitate this process. However, cyclic variability of SI engine demands that multicycle results are required to capture the extreme conditions. In addition, Mach Courant–Friedrichs–Lewy (CFL) number of 1 is desired to accurately predict the knock intensity (KI), resulting in unaffordable computational cost. In this study, a new approach to numerically predict KLSA using large Mach CFL of 50 with ten consecutive cycle simulation is proposed. This approach is validated against the experimental data for a boosted SI engine at multiple loads and spark timings with good agreements in terms of cylinder pressure, combustion phasing, and cyclic variation. Engine knock is predicted with early spark timing, indicated by significant pressure oscillation and end-gas heat release. Maximum amplitude of pressure oscillation analysis is performed to quantify the KI, and the slope change point in KI extrema is used to indicate the KLSA accurately. Using a smaller Mach CFL number of 5 also results in the same conclusions, thus demonstrating that this approach is insensitive to the Mach CFL number. The use of large Mach CFL number allows us to achieve fast turn-around time for multicycle engine CFD simulations.

Assessing Combustion Performance of a Diesel Reciprocating Engine Under Various Fuel Blends Using a Calculus-Statistical Time-Series Vibration Based Approach

The increasing use of biofuels in recent years has resulted in renewed consideration of compression ignition (CI) engines for power generation. However, the differences in chemical properties of these fuels have led to some variation in key engine performance parameters. Accordingly, researchers have begun to investigate the use of vibration-based approaches in assessing these behaviors. Despite some progress in assessing the use of diesel in CI engines, very little has been done on assessing the use of fuel blends. The current work, therefore, proposes a vibration-based approach to assessing engine performance in CI engines. It hypothesizes that the variation in cylinder pressure with combustion can be effectively monitored via engine vibration signals. It further proposes the use of a hybrid calculus-statistical method for the analysis of the vibration data. Accordingly, tests were conducted using a single-cylinder engine made to operate on different fuel blends. Conventional thermodynamic data were recorded during its operation. These data were used to calculate fundamental engine performance indicators. Simultaneously, vibration data were collected from the engine using an accelerometer mounted on the engine casing. The vibration data were analyzed using a matlab algorithm. The results showed that the proposed method is able to track the variations in combustion performance, for changes in the fuel used. More importantly, based on the approach, a parameter, which characterizes the nature of combustion taking place, is proposed. The approach proves to be a feasible method for assessing combustion performance of different fuels in CI engines, with minimal computational requirements.

Computational Investigation of Porous Media Combustion Technology in Spark Ignition Engine

In the present work, computational fluid dynamics approach is adopted to study the possibility of using porous media in combustion and emission in a single-cylinder four-stroke spark ignition engine. The combustion behavior inside the engine without and with application of porous media is studied. The analysis with application of PM signifies enhanced combustion behavior. The compression ratio is kept at 7. Two different types of fluid computational domains are considered, namely, without and with PM. The three-dimensional modeling, meshing and simulations of the combustion chambers are performed with the ANSYS 17.1-FLUENT software. The k–e turbulence model, the premixed combustion model and the spark ignition model are used in the study. The parameters to be analyzed are the variation of cylinder pressure, temperature and turbulence at different crank angles. The results of the computational work without PM are validated with the experimental work, which is executed on the research engine setup operated in SI mode. The work is performed at different engine loads by varying the engine torque, viz. 6 Nm (25%), 12 Nm (50%), 18 Nm (75%) and 24 Nm (100%) along with the no-load condition. The analyses of the results indicate that the peak value of total pressure (1,986,868.99 Pa) and average value of total temperature (632.63 K) with PM at 100% load are lower than without PM (1,992,314.50 Pa and 604.81 K). The concentrations of NOX emissions are significantly reduced by the use of PM for all the loads. The percentage reductions in NOX emissions at no load, 25%, 50%, 75% and 100%, are found to be 2.5%, 11.1%, 9.4%, 9% and 2.12%, respectively.

Optical analysis of flame inception and propagation in a lean-burn natural-gas spark-ignition engine with a bowl-in-piston geometry

Heavy-duty diesel engines can convert to lean-burn natural-gas spark-ignition operation through the addition of a gas injector in the intake manifold and of a spark plug in place of the diesel injector to initiate and control combustion. However, the combustion phenomena in such converted engines usually consist of two distinct stages: a fast-burning stage inside the piston bowl followed by a slow-burning stage inside the squish area. This study used flame luminosity data and in-cylinder pressure measurements to analyze flame propagation inside a bowl-in-piston geometry. The experimental results showed a low coefficient of variation and standard deviation of peak cylinder pressure, moderate rate of pressure rise, and no knocking for the lean-burn (equivalence ratio 0.66), low-speed (900 r/min), and medium-load (6.6 bar IMEP) operating condition. Flame inception had a strong effect on the flame expansion velocity, which increased fast once the flame kernel established, but it reduced near the bowl edge and the entrance of the narrow squish region. However, the burn inside the bowl was very fast. In addition, the long duration of burn inside the squish indicated a much lower flame propagation speed for the outside-the-bowl combustion, which contributed to a long decreasing tail in the apparent heat release rate. Furthermore, cycles with fast flame inception and fast burn inside the bowl had a similar end of combustion with cycles with delayed flame inception and then a retarded burn inside the bowl, which indicated that the combustion inside the squish region determined the combustion duration. Overall, the results suggested that the spark event, the flame development inside the piston bowl, and the start of the second combustion stage affected the phasing and duration of the two combustion stages, which (subsequently) can affect engine efficiency and emissions of diesel engines converted to a lean-burn natural-gas spark-ignition operation.

Comparison of combustion characteristics of an automotive CRDI engine with conventional HCV engine

In this present work, combustion parameters of an automotive CRDI diesel engine was investigated. A three cylinder CRDI passenger car engine employed with split injection pattern was tested at two different operating conditions namely, operating the engine at different speeds by maintaining a constant engine torque and also at different torques by maintaining a constant engine speed. Variation of combustion parameters of the engine was presented as function of BMEP, speed and torque. The variation of cylinder pressure and heat release rate of the CRDI engine was compared with a four stroke, six cylinder, heavy commercial vehicle (HCV) direct injection automotive engine employed with mechanical fuel injection system and significant variation was observed between the two. In the CRDI engine the magnitude of the cylinder pressure varied marginally during the combustion period when compared with mechanical fuel injection engine and the effect of split injection was observed in the heat release curve of the CRDI engine. Variation of start of combustion, peak pressure, maximum rate of pressure rise, maximum heat release rate and combustion duration with respect to speed and torque was presented for CRDI engine. [Received: May 23, 2016; Accepted: June 7, 2017]

Comparison of combustion characteristics of an automotive CRDI engine with conventional HCV engine

In this present work, combustion parameters of an automotive CRDI diesel engine was investigated. A three cylinder CRDI passenger car engine employed with split injection pattern was tested at two different operating conditions namely, operating the engine at different speeds by maintaining a constant engine torque and also at different torques by maintaining a constant engine speed. Variation of combustion parameters of the engine was presented as function of BMEP, speed and torque. The variation of cylinder pressure and heat release rate of the CRDI engine was compared with a four stroke, six cylinder, heavy commercial vehicle (HCV) direct injection automotive engine employed with mechanical fuel injection system and significant variation was observed between the two. In the CRDI engine the magnitude of the cylinder pressure varied marginally during the combustion period when compared with mechanical fuel injection engine and the effect of split injection was observed in the heat release curve of the CRDI engine. Variation of start of combustion, peak pressure, maximum rate of pressure rise, maximum heat release rate and combustion duration with respect to speed and torque was presented for CRDI engine. [Received: May 23, 2016; Accepted: June 7, 2017]