Rakesh Kumar Maurya

Experimental investigation of the effect of the intake air temperature and mixture quality on the combustion of a methanol- and gasoline-fuelled homogeneous charge compression ignition engine

Abstract Environmental concerns have increased significantly all over the world in the past decade. To fulfil the simultaneous emission requirements for near-zero pollutant and low carbon dioxide (CO2) levels, which are the challenges for the future powertrains, many studies are currently being carried out on new engine combustion processes, such as controlled autoignition for gasoline engines and homogeneous charge compression ignition (HCCI) for diesel engines. These combustion processes have the potential for ultra-low nitrogen oxide (NO x ) and particulate matter emissions in comparison with conventional gasoline or diesel engines. In this paper, the combustion characteristics of a HCCI engine fuelled with methanol and gasoline were investigated on a modified two-cylinder four-stroke engine. The port fuel injection technique is used to prepare a homogeneous charge of fuel and air. The experiment is conducted with various intake air temperatures ranging from 120°C to 160°C at different air-to-fuel ratios, for which stable HCCI combustion is achieved. The experimental results indicate that the inlet air temperature and air-to-fuel ratio have a significant effect on the maximum in-cylinder pressure and its position relative to top dead centre, the shape of the pressure rise curve, and the heat release rates. The results confirm that the inlet air temperature is a very sensitive parameter in controlling combustion timing and thus the effectiveness of the HCCI combustion process.

Experimental Investigation of Cycle-by-Cycle Variations in CAI/HCCI Combustion of Gasoline and Methanol Fuelled Engine

The development of vehicles continues to be determined by increasingly stringent emissions standards including CO2 emissions and fuel consumption. To fulfill the simultaneous emission requirements for near zero pollutant and low CO2 levels, which are the challenges of future powertrains, many research studies are currently being carried out world over on new engine combustion process, such as Controlled Auto Ignition (CAI) for gasoline engines and Homogeneous Charge Compression Ignition (HCCI) for diesel engines. In HCCI combustion engine, ignition timing and combustion rates are dominated by physical and chemical properties of fuel/air/residual gas mixtures, boundary conditions including ambient temperature, pressure, and humidity and engine operating conditions such as load, speed etc. Because of large variability of these factors, wide cycle-to-cycle variations are observed in HCCI combustion engines, similarly small variations in ignition timing and combustion rates result in wide variation in engine performance and emissions. Also, cycle-to-cycle combustion variations result in objectionable engine noise and vibrations. As a result of wide cycle-to-cycle variations, HCCI combustion can be achieved in an engine for narrow range of lean and rich operating limits. This motivates the researchers to systematically investigate mechanism and control of cycle-to-cycle variations on HCCI engines. In this paper, the combustion stabilities and cycle-tocycle variations of a HCCI combustion engine fuelled with gasoline and methanol were investigated on a modified two-cylinder, four-stroke engine. In this investigation, port fuel injection technique is used for preparing homogeneous charge. The experiment is conducted with variable intake air temperature at different air-fuel ratios at constant engine speed. Incylinder pressure of 100 combustion cycles for each test condition was recorded. Consequently, cycle-to-cycle variations of the main combustion parameters and performance parameters were analyzed and evaluated. To evaluate the cycle-to-cycle variations of HCCI combustion parameters at various test conditions, coefficient of variation (COV) of each parameter was used. The results show that critical parameters, which can be used to define HCCI operating range, are maximum rate of pressure rise, and COV of indicated mean effective pressure (IMEP).

Experimental Investigation of Close-Loop Control of HCCI Engine Using Dual Fuel Approach

Homogeneous Charge Compression Ignition (HCCI) offers great promise for excellent fuel economy and extremely low emissions of NO x and PM. HCCI combustion lacks direct control on the ‘start of combustion’ such as spark timing in SI engines and fuel injection timing in CI engines. Auto ignition of a homogeneous mixture is very sensitive to operating conditions of the engine. Even small variations of the load can change the timing from ‘too early’ to ‘too late’ combustion. Thus a fast combustion phasing control is required since it sets the performance limitation of the load control. Crank angle position for 50% heat release is used as combustion phasing feedback parameter. In this study, a dual-fuel approach is used to control combustion in a HCCI engine. This approach involves controlling the combustion heat release rate by adjusting fuel reactivity according to the conditions inside the cylinder. Two different octane fuels (methanol and n-heptane) are used for the study. Port fuel injection technique is used for preparing homogeneous mixture of methanol, heptane and air using two separate injectors for methanol and heptane. Close loop control of combustion phasing is attained by instantaneous variation of fuel ratio of methanol and n-heptane while maintaining the injected fuel energy constant. Total fuel energy injected is used to control the IMEP of the engine. It is found that controller is able to keep close track of the reference combustion phasing using PID control by changing the fuel ratio. PID control of combustion phasing and IMEP using dual fuel is achieved and is successfully demonstrated in the HCCI engine in the study.

Combustion and Emission Behavior of Ethanol Fuelled Homogeneous Charge Compression Ignition (HCCI) Engine

The Homogeneous charge compression ignition (HCCI) is the third alternative for the combustion in the reciprocating engine. HCCI a hybrid of well-known spark ignition (SI) and compression ignition (CI) engine concepts and has potential of combining the best features of both. A two cylinder, four stroke, direct injection diesel engine was modified to operate one cylinder on the compression ignition by detonation of homogeneous mixture of ethanol and air. The homogeneous mixture of the charge is prepared by port injection of ethanol in the preheated Intake air. This study presents results of experimental investigations of HCCI combustion of ethanol at intake air temperature of 120 0 C and at different air-fuel ratios. In this paper, the combustion parameters, pressure time history, rate of pressure rise, rate of heat release, mean temperature history in the combustion chamber is analyzed and discussed. The HCCI operating region criteria is defined based on the cycle-to-cycle variation of indicated mean effective pressure (IMEP) and rate of pressure rise. The results presented in this study for air fuel ratio, which satisfies the HCCI operating region criteria. The results show that controlled HCCI combustion is possible with extremely low emission and high efficiency.

Effect of intake air temperature and air–fuel ratio on particulates in gasoline and n-butanolfueled homogeneous charge compression ignition engine:

An experimental study was conducted to investigate the effect of engine operating parameters on exhaust particulate size–number distribution in a homogeneous charge compression ignition engine fueled with gasoline and n-butanol. In this investigation, portfuel injection was done for preparing homogeneous charge, and intake air preheating was used for auto-ignition of the charge. Engine exhaust particle sizer was used for measuring size–number distribution of particulate matter emitted from the homogeneous charge compression ignition engine. Experiments were conducted at different engine speeds by varying intake air temperature and air–fuel ratio of the charge. Effect of engine operating parameters on particulate size–number distribution, size–surface area distribution, and total particulate number concentration was investigated. Most significant particle numbers were in the range of 6–150 nm mobility diameter for all test conditions. n-Butanol showed relatively higher peak number concentration and lower mobility diameter corresponding to the peak concentrations as compared to baseline gasoline. On increasing intake air temperature, mobility diameters corresponding to peak number concentration of particles moved towards lower mobility diameters. Count mean diameter of particles was in the range of 35–80 nm and 20–65 nm for gasoline and n-butanol, respectively, for all test conditions in homogeneous charge compression ignition operating range.

Experimental Investigation of Cyclic Variation in a Diesel Engine Using Wavelets

In this study, cyclic variations of combustion parameters (IMEP and THR) are analyzed using morlet wavelet transform in a diesel engine. Experiments were conducted at 1500 rpm for different engine load conditions and compression ratios. Combustion parameters were calculated from measured cylinder pressure trace. In-cylinder pressure data of 2500 consecutive engine cycles were acquired and processed for the analysis of cyclic variations. Results revealed that cyclic variability in THR decreases with increase in engine load and compression ratio. Cyclic variability is highest in idle load conditions at lowest compression ratio. Low frequency cyclic variations are observed at low loads conditions and with increase in engine load variations shift to high frequency range. Results can be utilized for the development of effective engine control strategies.

Particulate Morphology and Toxicity of an Alcohol Fuelled HCCI Engine

Homogeneous charge compression ignition (HCCI) engines are attracting attention as next-generation internal combustion engines mainly because of very low NOx and PM emission potential and excellent thermal efficiency. Particulate emissions from HCCI engines have been usually considered negligible however recent studies suggest that PM number emissions from HCCI engines cannot be neglected. This study is therefore conducted on a modified four cylinder diesel engine to investigate this aspect of HCCI technology. One cylinder of the engine is modified to operate in HCCI mode for the experiments and port fuel injection technique is used for preparing homogenous charge in this cylinder. Experiments are conducted at 1200 and 2400 rpm engine speeds using gasoline, ethanol, methanol and butanol fuels. A partial flow dilution tunnel was employed to measure the mass of the particulates emitted on a pre-conditioned filter paper. The collected particulate matter (PM) was subjected to chemical analyses in order to assess the amount of Benzene Soluble Organic Fraction (BSOF) and trace metals (marker of toxicity) using Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). Field emission scanning electron microscope (FE-SEM) was used for particulate morphology investigations at 1000X and 5000X resolution. Trace amount of particulates were observed on the filter paper for the test fuels. The concentration of different trace metals analyzed also showed decreasing trends with increasing engine loads.

Optimization of engine operating conditions and investigation of nano-particle emissions from a non-road engine fuelled with butanol/diesel blends

ABSTRACT This study presents the experimental investigation of performance and emission characteristics (including nano-particle emissions) of a non-road diesel engine fuelled with neat diesel and butanol/diesel blends. Experiments were performed at optimal engine operating conditions for a constant engine speed of 1500 rpm. To find the optimal engine operating conditions, first experiments were conducted using diesel fuel. Engine operating parameters were optimized for higher brake thermal efficiency and lower exhaust emissions (i.e. gaseous as well as nano-particle emissions). Taguchis design of experiment was used to optimize the compression ratio, injection pressure and engine operating load. To investigate the effect of butanol blends on the performance and emissions characteristics, experiments were conducted at three different butanol/diesel blend ratios (i.e. 10, 20 and 30% of butanol by volume) at optimum engine operating conditions. Results indicate that butanol/diesel blends have the potential to reduce CO, NO and particle emissions. The results also revealed that the concentration of ultrafine particle number reduces with diesel/butanol blends for all tested load conditions. The highest reductions in total particle number concentration for all butanol blends were found at 25% and 50% engine load conditions, as compared to neat diesel.

Investigation of Effect of Butanol Addition on Cyclic Variability in a Diesel Engine Using Wavelets

This study focuses on the experimental investigation of the cyclic variations of maximum cylinder pressure (Pmax) in a stationary diesel engine using continuous wavelet transform. Experiments were performed on a stationary diesel engine at a constant speed (1500 rpm) for low, medium and high engine load conditions with neat diesel and butanol/diesel blends (10%, 20%, and 30% butanol by volume). In-cylinder pressure history data was recorded for 2000 consecutive engine operating cycles for the investigation of cyclic variability. Cyclic variations were analyzed for maximum cylinder pressure. The results indicated that variations in the Pmax is highest at lower load condition and decreases with an increase in the engine load. Global wavelet spectrum (GWS) power decreases with an increase in the engine operating load indicating decrease in cyclic variability with the engine load. The results also revealed that lower cyclic variations obtained with butanol/diesel blends in comparison to neat diesel.

Investigation of Deterministic and Random Cyclic Patterns in a Conventional Diesel Engine Using Symbol Sequence Analysis

Current study focuses on cyclic variability analysis of indicated mean effective pressure (IMEP) and total heat release (THR) in a conventional single cylinder diesel engine using symbol sequence statistics. The objective is to characterize the cyclic variations and estimate the deterministic pattern in experimental data series. Results presented in this study can be beneficial for the design of effective control strategy. Experiments are performed at constant speed for five different engine operating conditions. Engine cylinder pressure data is acquired for 2500 consecutive cycles. Engine combustion parameters (IMEP and THR) are calculated from measured cylinder pressure on cycle to cycle basis and resulting data series is analyzed by symbol sequence method. Results revealed that selection of symbol sequence length and number of partitions is dependent on engine operating conditions and chosen combustion parameter.