Compressed Natural Gas Injection Research Articles

Converting compression ignition engine to dual-fuel (diesel + CNG) engine and experimentally investigating its performance and emissions

Abstract One of the suitable solutions for burning natural gas in diesel engines is the use of dual-fuel technology. In this study, the MT440C compression ignition engine has been converted to dual fuel (diesel + CNG) simultaneously combustion of diesel fuel and natural gas, with the least amount of engine changes and using the most amount of natural gas. The ignition of the engine was in the range of the governor. Experiments in stable conditions for the working modes of the engine were performed with pure diesel fuel and mixed gas diesel fuel. The effects of natural gas fuel as the main fuel and diesel fuel as the spark ignition on a 4-cylinder compression ignition engine were investigated on the performance and emissions. According to the engine speed and load, the amount of diesel-fuel injection was adjusted by making mechanical changes in the governor, while the ignition system was not used. These tests were performed at engine speeds of 1,200, 1,400, 1,600, 1,800, and 2,000 rpm, using single diesel fuel and dual fuel (diesel + CNG). These data were collected in the Engine Research Center of Tabriz Motorsazan Company, and experimental runs were repeated three times One of the goals of this research is to reduce the consumption of diesel fuel, and in the current study, compressed natural gas (CNG) is 72% and diesel is 28% of the dual fuel in idling. This study showed that the emission of some pollutants increased and some decreased in the dual-fuel mode. Therefore, more research is needed on modifying the diesel injection system as a spark plug or the CNG injection system to reduce the emission of greenhouse gases.

The Effects CNG Injection Timing on Engine Performance and Emissions Of A Diesel Dual Fuel Engine

Sequential combustion process on diesel dual fuel engine with compressed natural gas (CNG) fuel was complex. The problems of diesel dual fuel with CNG gas are reduced thermal efficiency and resulting in high carbon monoxide (CO) and unburned hydrocarbon (HC) emissions. The right setting between combustion air, diesel pilot fuel, and CNG gas fuel can improvement the performance and emissions. The experiment was conducted with diesel fuel conventional and dual fuel mode with CNG fuel in a single cylinder, four strokes, constant speed (1500 rpm) diesel engine type diamond DI 800. Performance parameters such as thermal efficiency and specific fuel consumption (SFC), emissions such as CO, HC, and smoke density are determined at five starts of injection timing (SOI) CNG of 700CA, 900CA, 1100CA, 1300CA, dan 1500CA ATDC with ECU programmable of Vemstune software. The results indicated that retarded CNG injection timings improved engine performance and emissions diesel dual fuel. Start of CNG injection timing optimization at 1300CA ATDC with increased thermal efficiency 14,35% and decreased specific fuel consumption (SFC) 8,83 % . in addition, it decreased CO emissions 21,35%, HC emissions 17,93%, and PM emissions lower 34,98%. However, engine performance diesel dual fuel lower than a conventional diesel engine.

Injection characteristics study of high-pressure direct injector for Compressed Natural Gas (CNG) using experimental and analytical method

The injection characteristics of direct injector affect the mixture formation and combustion processes. In addition, the injector is converted from gasoline operation for CNG application. Thus measurement of CNG direct injector mass flow rate was done by independently tested a single injector on a test bench. The first case investigated the effect of CNG injection pressure and the second case evaluate the effect of pulse-width of injection duration. An analytical model was also developed to predict the mass flow rate of the injector. The injector was operated in a choked condition in both the experiments and simulation studies. In case 1, it was shown that mass flow rate through the injector is affected by injection pressure linearly. Based on the tested injection pressure of 20 bar to 60 bar, the resultant mass flow rate are in the range of 0.4 g/s to 1.2 g/s which are met with theoretical flow rate required by the engine. However, in Case 2, it was demonstrated that the average mass flow rate at short injection durations is lower than recorded in Case 1. At injection pressure of 50 bar, the average mass flow rate for Case 2 and Case 1 are 0.7 g/s and 1.1 g/s respectively. Also, the measured mass flow rate at short injection duration showing a fluctuating data in the range of 0.2 g/s - 1.3 g/s without any noticeable trends. The injector model able to predict the trend of the mass flow rate at different injection pressure but unable to track the fluctuating trend at short injection duration.

Effect of compression ratio, CNG flow rate and injection timing on the performance of dual fuel engine operated on honge oil methyl ester (HOME) and compressed natural gas (CNG)

The present work is an effort towards the reduction of exhaust emissions from diesel engine operated in the dual fuel (DF) mode using a combination of renewable and fossil fuels. An experimental investigation has been carried out to study the performance, combustion and exhaust emissions of a single cylinder, four stroke, water cooled, direct injection (DI) diesel engine operated on Honge oil methyl ester (HOME) as the injected fuel and CNG as the inducted fuel by varying the compression ratio, CNG flow rate and injection timing. The experiments were planned as per the full factorial design (FFD) to minimize the number of experiments. The response surface methodology (RSM) based quadratic models have also been developed to establish the relationships between the identified parameters and the proposed characteristics. The response surface analysis indicates that increasing the compression ratio with advanced injection timing and low CNG flow rate help to improve the performance of DF engine fueled with HOME and CNG in terms of the increased brake thermal efficiency (BTE) and reduced emissions (Smoke, Carbon monoxide, Hydrocarbon) except the oxides of nitrogen (NOx) emissions. Ignition delay (ID), as well as combustion duration decreased with advanced injection timing, injector opening pressure (IOP) and the compression ratio (CR), while the peak pressure and heat release rate (HRR) increased.

Effect of Diesel–Ethanol–PPME (Pongamia piñata Methyl Ester) Blends as Pilot Fuel on CNG Dual-Fuel Operation of a CI Engine: A Performance-Emission Trade-Off Study

The major portion of today’s natural gas dual-fuel engines use pilot amounts of diesel as the igniter fuel. However, it is found that dual-fuel operation of natural gas with pilot diesel poses problems, such as reduced brake thermal efficiency and increased hydrocarbon emission. The present experimental work explores the potential of compressed natural gas (CNG) under dual-fuel operation by utilizing two blends of diesel–ethanol–Pongamia piñata methyl ester (PPME) as pilot fuel. The blends, namely, D45E15B40 (45% diesel, 15% ethanol, 40% PPME) and D30E20B50 (30% diesel, 20% ethanol, 50% PPME) are selected on the basis of biodiesel-assisted miscibility of ethanol in diesel. It is found from the study that the pilot operation of D45E15B40 blend increases the brake thermal efficiency by 43.5% and 26.4% at 80% and 100% load conditions with CNG injection for 23 000 μs, whereas D30E20B50 produces an increase of 51.7% and 46.5% under the same conditions in comparison with pilot diesel operation. The NOx emission from the engine is also decreased by 37.3% and 21.6% at 80% and 100% load conditions by D45E15B40 and 33.9% and 15.9% by D30E20B50 blend, as compared to pilot diesel operation. The trade-off study in the present work reveals encouraging aspects of D45E15B40 and D30E20B50 blends as it is found that pilot operation with these blends can stretch the usability range of CNG injection duration to 9000 μs.

Modelling aspects of a CNG injection system to predict its behavior under steady state conditions and throughout driving cycle simulations

Alternative fuels such as compressed natural gas (CNG) have lately gained an increasing interest due to the even more stringent emission regulations and environmental policies. Considerable R&D activity has been carried out in order to enhance the mixture formation and to improve the after treatment efficiency. The achievement of these goals cannot disregard the importance of the injection system and of its component (common rail, injectors and pressure reducing valve) on the air-to-fuel mixing. The amount of injected fuel should in fact be properly targeted by the ECU basing on the estimation of the induced air and accounting for the embedded closed-loop strategies. Still, these latter are normally derived from engine-base routines and totally ignore the injection system dynamics.The present paper aims at developing a thorough model of the injection system with specific attention to the one component which significantly contributes to fully defining its dynamic response, i.e. the pressure reducing valve. The pressure reducer is made up of various elements that retain diverse weights on the valve behavior and should consequently be differently addressed to. The research has been focused on defining the set of parameters to be precisely reproduced in the 0D-1D simulation so as to match the injection system experimental behavior. A refined model of the pressure reducer has hence been proposed and the model has been calibrated, tested and run under various operating conditions so as to assess for the set-up validity.Comparisons have been carried out on steady state points as well as through out a vehicle driving cycle and the model capability to properly reproduce the real system characteristic has been investigated into. The proposed valve model has proved to consistently replicate the injection system response for different speed and load conditions. A few methodological indications concerning modeling aspects of a pressure regulator can be drawn from the present study.Finally, the model has been run in a predictive mode so as to inquiry into the response of the system to fast transient operations, both in terms of speed and load. The model outputs have highlighted mismatches between the ECU target mass and the actually injected one and have hinted at the need for dedicated and refined control strategies capable of preventing anomalies in the mixture formation and hence in the engine functioning.

Fluid-dynamic and numerical aspects in the simulation of direct CNG injection in spark-ignition engines

This paper presents a detailed discussion on the numerical simulation of the underexpanded gas efflux from an outward-opening poppet-valve injector into an engine combustion chamber. The aim of the paper is to optimize the numerical simulation strategy for direct gas injection, in view of its application to internal combustion (IC) engines. In the first part of the paper, the widely studied case of a two-dimensional compressible flow is examined, and the main guidelines for the development of an effective numerical model for compressed natural gas (CNG) direct injection simulation are given, with specific reference to IC engines. The second part of the paper is devoted to the description of the numerical model developed and validated by the authors within the Star-CD environment, which is characterized by the presence of two distinct meshes. The first is built manually and covers the region surrounding the injector exit, whereas the second one covers most of the engine chamber and is built using the Es-ICE tool. A careful grid-independence study has been carried out in both the first and second part of the paper, and the influence of the spatial discretization of the convective fluxes has been discussed as well.The analyses have shown that a resolution of 40 cells in the nozzle height should be adopted to describe the typical phenomena that characterize an underexpanded free jet, unless a second order scheme can be implemented. However, as far as the simulation of the jet penetration time-history and its mixing with the surrounding air is concerned, sufficiently accurate results can also be obtained by using 20 cells per nozzle diameter and the first-order upwind scheme. As for the direct injection engine model, 16 cells across the nozzle lift represent a good compromise between accuracy and reliability of the results and the required computational time. The model has been validated with the support of experimental PLIF images in an optical-access engine, and has shown overall good accuracy and reliability, thus suggesting it is suitable for mixture formation analysis.

Effect of compressed natural gas dual fuel operation with diesel and Pongamia pinnata methyl ester (PPME) as pilot fuels on performance and emission characteristics of a CI (compression ignition) engine

The experimental work presents a comparative study of performance and emission using Pongamia pinnata methyl ester (PPME) and Diesel as pilot fuel in a CI (compression ignition) engine with compressed natural gas (CNG) as the primary fuel. The results show that PPME–CNG dual fuel operation is more effective than Diesel–CNG dual fuel operation in improving the performance and emission characteristics of the engine. CNG is found to share higher quantity of input energy with PPME pilot operation than pilot Diesel operation. Low amount of CNG injection also increases the brake thermal efficiency of the engine. PPME–CNG operations with low amount of CNG injections are also more instrumental in reducing CO (carbon monoxide) emission and smoke opacity than Diesel–CNG operations. NOx emission from the engine is found to increase a bit for PPME–CNG operations in comparison to Diesel–CNG operation. PPME–CNG operation is also more effective in reducing hydrocarbon emission than Diesel–CNG operations. The study also shows that CNG injected at 10° ATDC (after top dead center) for a duration of about 4500 μs with PPME as pilot fuel can produce better performance and emission signatures than Diesel–CNG operation. The tradeoff study also consolidates the fact that PPME–CNG dual fuel operation is instrumental in resolving the high performance–low emission paradox.

Effect of mixing chamber venturi, injection timing, compression ratio and EGR on the performance of dual-fuel engine operated with HOME and CNG

Stringent environmental policies and the ever increasing demand for energy have triggered interest in novel combustion technologies that use alternative fuels as energy sources. Of these, pilot-ignited compressed natural gas (CNG) engines that employ small biodiesel pilot to ignite a premixed natural gas–air mixture have received considerable attention. This paper discusses the effect of mixing chamber venturi, injection timing, compression ratio and exhaust gas recirculation (EGR) on the performance of dual-fuel engine operated on biodiesel derived from honge oil and is called honge oil methyl ester (HOME) and CNG. The proposed study mainly focuses on the manifold induction of CNG along with HOME injection. However, CNG can also be injected using port or direct gas injector (Lakshmanan and Nagarajan 2010, Energy 35, pp. 3172–3178). The future study will involve these methods of CNG injection. From this study, it is concluded that an advanced injection timing and an increased compression ratio resulted in increased brake thermal efficiency and reduced smoke, hydrocarbons and carbon monoxide emissions. However, nitrogen oxides (NO x ) emission increased significantly. The increased NO x emission was effectively reduced with EGR method. A mixing chamber venturi of 3 mm size, injection timing of 27° before top dead centre (BTDC), compression ratio of 17.5 and 10% EGR were found to be optimum for the modified compression ignition engine that was operated on CNG–HOME dual-fuel mode.

Kriging metamodel management in the design optimization of a CNG injection system

This paper deals with the use of Kriging metamodels in multi-objective engineering design optimization. The metamodel management issue to find the tradeoff between accuracy and efficiency is addressed. A comparative analysis of different strategies is conducted for a case study devoted to the design of a component of the injection system for Compressed Natural Gas (CNG) engines. The computational results are reported and analyzed for a performance assessment conducted with a data envelopment analysis approach.

Modelling and predictive control of a new injection system for compressed natural gas engines

In internal combustion engines equipped with the common rail injection system the accurate metering of the air/fuel mixture strictly depends on the pressure regulation. Accuracy in metering is difficult to be achieved especially for compressed natural gas (CNG) injection systems, as the gas compressibility makes the fuel delivery process more complex. Since the controller design requires a model of the injection system, this paper presents a physics-based state-space model of an innovative CNG injection system. The model parameters only depend on well defined geometrical data and fuel properties. Comparing simulation and experimental results in different operating conditions validates the model. Further, the proposed model is used for designing a generalized predictive controller for the injection pressure regulation, which is implemented in few steps. Experimental results show the effectiveness of the proposed approach.