Intake Valve Research Articles

Effect of boosting on a performance and emissions in a port fuel injection natural gas engine with variable intake and exhaust valve timing

Recently, many studies have been conducted on the conversion of conventional fossil fuels to alternative fuels. Natural gas is one of the best alternative fuels because it is a low-carbon fuel. In natural gas engines, port fuel injection is generally adopted rather than direct injection because of the compatibility of the injection system in a positive ignition engine. However, methane, of which the global warming potential is 28 times than that of carbon dioxide, is highly likely to emit during the valve overlap in port fuel injection engines. The methane slip phenomenon could be reduced by changing the intake and exhaust valve timing. However, few studies have discussed engine performance and emission characteristics through valve timing changes in natural gas engines. Therefore, in this study, experiments were conducted under the valve timing variations with/without boosting in a natural gas engine. Through experiments, it was possible to investigate the trend of engine performance and methane emission according to the change in the intake and exhaust valve timing. As a result, under the boosted condition, the intake valve timing could only be advanced up to 45 CAD bTDC and the exhaust valve timing could only be retarded by 27.4 CAD bBDC. This is because the methane slip phenomenon increased and it resulted in a decrease of engine torque when the intake valve timing was excessively advanced or the exhaust valve timing was inordinately retarded under the boosted condition. In addition, considering a level of methane emission equivalent to EURO-6, the valve timings were optimized for each engine speed point of 1000–2500 rpm under boosted high load conditions. It was found that the trend of intake valve timing of the natural gas engine was unlike that of the conventional gasoline engine under the low engine speed of less than 2500 rpm.

A Study of the Impact of Methanol, Ethanol and the Miller Cycle on a Gasoline Engine

This paper focuses on the investigation and optimisation of the Miller cycle, methanol, ethanol and turbocharging when applied to a high-performance gasoline engine. These technologies have been applied both individually and concurrently to test for potential compounding effects. Improvements have been targeted with regards to both emission output and performance. Also assessed is the capability of the engine to operate when exclusively powered by biofuels. This has been carried out numerically using the 1D gas dynamics tool ‘WAVE’, a 1D Navier–Stokes equation solver. These technologies have been implemented within the McLaren M838T 3.8L twin-turbo engine. The Miller cycle early intake valve close (EIVC) improved peak efficiency by 0.17% and increased power output at low and medium loads by 11%. Reductions of 6% for both NOx and CO were also found at rated speed. The biofuels achieved NOx and CO reductions of 60% and 96% respectively, alongside an efficiency increase of 2.5%. Exclusive biofuel use was found to be feasible with a minimum 35% power penalty. Applied cooperatively, the Miller cycle and biofuels were not detrimental to each other, compounding effects of a further 0.05% efficiency and 2% NOx improvements were achieved.

Flow directed spark stretch and flame propagation in a high-tumble production engine

This study performs endoscopic high-speed imaging to enhance the fundamental knowledge of in-cylinder flow structure and flame development process in a selected high-tumble production engine. The endoscopic high-speed particle image velocimetry (eHS-PIV) was performed for varied engine speeds and intake valve closing (IVC) timings to evaluate their impact on the in-cylinder flow structure in a motored engine condition. On another endoscope engine sharing the same hardware, high-speed flame imaging was conducted to visualise spark stretch and flame propagation. The flow and flame measurements were repeated for over 100 cycles and the ensemble-averaged results are compared. The eHS-PIV showed that a strong tumble vortex is generated during the piston compression with the flow directed towards the exhaust side. As the piston reaches top dead centre (TDC), however, a complex flow breakup involving multiple flow components occurs. This is followed by lateral flow vectors travelling back towards the intake side, which is termed as the bounce-back flow. For a tested engine speed range of 1700–2700 revolutions per minute (rpm), 2500 rpm shows the most significant bounce-back flow as a result of competition between the remaining exhaust-ward tumble flow strength and the newly formed bounce-back flow strength. At a retarded IVC timing, the flow loss leads to a weakened tumble flow and subsequently no bounce-back flow formation to maintain the exhaust-ward TDC flow direction. From the comparison between the flow results and spark/flame high-speed images, a strong positive correlation is found between the TDC flow direction and spark plasma stretch, and subsequently the flame propagation direction. The findings indicate that the TDC flow direction should be considered as a key parameter in the engine design and operating condition settings.

Stereoscopic Micro PIV Investigation of Velocity Boundary Layer Near Piston Top of a Tumble Enhanced SI IC Engine

Stereoscopic Micro PIV Investigation of Velocity Boundary Layer Near Piston Top of a Tumble Enhanced SI IC Engine

A novel strategy of extremely delayed intake valve opening to improve the cold-start characteristics of a low compression ratio diesel engine

Combined in-cylinder and after-treatment emission control methods are generally adopted to meet the current stringent emission targets for diesel engines. It is well established that reducing the geometric compression ratio (CR) results in a simultaneous reduction in the oxides of nitrogen (NOx) and soot emissions in diesel engines. However, poor cold-start characteristics prevent extensive use of low compression ratio (LCR) diesel engines for automotive applications. In the present work, a novel extremely delayed intake valve opening (IVO) strategy is proposed to improve the cold-start characteristics of a light-duty LCR diesel engine. A commercial one-dimensional gas-exchange model was used to optimize the intake valve open and close timings. The results corresponding to a cranking speed of 200 rpm and ambient temperature of 0°C show that advancing the intake valve close (IVC) timing increases the effective compression stroke that can improve the cylinder temperature by 5%. Further, implementing ‘extremely delayed IVO’ by retarding the timing from 1°CA to 61°CA aTDC could help to further increase the cylinder temperature by 14% compared to the base timings. The delayed opening of the intake valve leads to a higher expansion of the cylinder mass, leading to a lower cylinder pressure before IVO and a higher intake air velocity immediately after IVO. With the higher intake air velocity, the incoming air’s kinetic energy is dissipated to increase the stagnation temperature, resulting in an overall benefit in cylinder temperature. The experimental measurements conducted in a cold chamber with the optimized IVO and IVC timings confirmed the benefits by achieving a better cold-startability of the LCR engine. In comparison, the LCR engine with the stock valve timings could be started only up to +5°C, the optimized valve timings could ensure startability up to −10°C without any starting aids. Thus, the proposed approach of adopting the optimized valve timings can help LCR diesel engines to overcome the limitations of cold-startability.

Experimental study on the approach for improved brake thermal efficiency on a two-stage turbocharged heavy-duty diesel engine

The approach to achieving improved brake thermal efficiency (BTE) for a heavy-duty diesel engine was studied by experiment analysis. The engine was designed on the basis of a two-stage turbocharger system (high-pressure (HP) turbine with variable geometry turbine) and a variable effective compression ratio through retarded intake valve closing timing. The cooperative control of minimum charge density, compressor efficiency, and compressor pressure ratio distribution was proposed to optimize the BTE. The interactive principle was then clarified. Results showed that the gross indicated thermal efficiency (ITEg) increased rapidly with charge density because of the promotion of the mixing rate. However, the increased charge density had a threshold, beyond which the pumping loss (PL) increased rapidly and thus impeded the ITEg growth rate. Therefore, a minimum charge density should correspond to mixing rate requirements. Moreover, the PL decreased with the decrease of the turbocharger driving power when the charge density was kept constant. Therefore, in the case of minimum charge density satisfying the mixing rate, the minimum turbocharger driving power should be limited to minimize PL by improving the compressor efficiency and optimizing the compressor pressure ratio distribution. At the core of the cooperative control of minimum charge density, compressor efficiency, and compressor pressure ratio distribution was thus identified as the simultaneous optimization of the mixing process and the gas exchange process. Such optimization contributed to the maximization of the BTE.

TKE Distribution According to the Intake Valve Angle in Steady Flow of the Pent-Roof SI Engine

TKE Distribution According to the Intake Valve Angle in Steady Flow of the Pent-Roof SI Engine

Effect of synergistic engine technologies for 48 V mild hybrid electric vehicles

48 V mild hybrid electric vehicles (MHEVs) are considered to the prospective near-term solution for cost-effective vehicle electrification. In this study, the fuel consumption improvement of various synergistic engine technologies was experimentally investigated with a 48 V P0 mild hybridization. The details of application and optimization for each technology were considered and the effect of each technology was quantitatively identified. A combination of synergistic engine technologies including a high compression ratio, late intake valve closing strategy, high tumble flow, electric supercharging and exhaust gas recirculation was applied to a 1.4 L PFI engine. Engine test results confirmed that fuel consumption could be significantly improved by these technologies, and the maximum power and torque were increased as well. The vehicle test results showed that the application of synergistic engine technologies improved vehicle fuel economy by 10%. Engine optimization and EGR could enhance the fuel economy by 5.5% and the effect of electric supercharging and downspeeding resulted in a 4.5% fuel economy improvement. These improvements through the engine technologies were greater than the effect of 48 V mild hybridization which was verified to be 5.5% of the fuel economy enhancement. The result suggests that the application of synergistic engine technologies will be highly effective for improving fuel efficiency of MHEV.

Numerical investigation and experimental validation on the leakage of methanol and formaldehyde in diesel methanol dual fuel engine with different valve overlap

The diesel methanol dual fuel (DMDF) engine is confronting with the problem of high unregulated emissions of methanol and formaldehyde. The previous studies on unregulated emissions of DMDF engine focused on the measuring methanol and formaldehyde concentrations in the exhaust without distinguishing whether emissions come from leakage during valve overlap or incomplete combustion in the cylinder. In this study, a computation fluid dynamics (CFD) model coupled with a detailed chemical kinetic mechanism was developed to investigate the methanol and formaldehyde emissions of DMDF engine. The results showed that the unburned methanol and formaldehyde in the cylinder were the main part of the total methanol and formaldehyde emissions based on the 41 °CA valve overlap of simulation model. Then the effects of different intake valve opening (IVO) and exhaust valve closing (EVC) on methanol emissions were investigated. The results showed that only increasing IVO or EVC had very little effect on the leakage of methanol during scavenging. However, when the IVO and EVC changed simultaneously, the valve lift would significantly increase during the valve overlap of scavenging, which had a great impact on methanol leakage. The simulation results were validated by experiments in a 6170 marine engine. The experimental results were consistent with the simulation results and the increase of effective flow area caused by valve lift during large valve overlap was the most important reason for the increase of methanol emission. Therefore, all engines have almost no leakage in small valve overlap. However, with the increase of valve overlap, the actual results were different due to the different valve lift and mixture concentration of different engines.

Lipschitz discrete observer design for HCCI engine mixed gas temperature at intake valve closed

The gas temperature for Homogeneous Charge Compression Ignition engine at intake valve closed is difficult to measure; so a Lipschitz discrete observer is designed. In particular, a single cylinder engine model is proposed. And, a thermodynamic process based state equation is presented considering the heat loss of residual exhaust gas. Consequently, a discrete nonlinear state observer is designed using Lipschitz condition. Finally, the numerical experiments are performed. The results demonstrate the effectiveness of the proposed observer in terms of the accuracy and robustness.

Effects of Intake Valve Lift Form Modulation on Exhaust Temperature and Fuel Economy of a Low-loaded Automotive Diesel Engine

Exhaust after-treatment (EAT) systems on automotive vehicles cannot perform effectively at low loads due to low exhaust temperatures (Texhaust < 250oC). Con-ventional late intake valve closure (LIVC) technique - a proven method to im-prove diesel exhaust temperatures - generally requires the modulation of the whole valve lift profile. However, an alternative method - boot-shaped LIVC - only needs partial lift form modulation and can rise exhaust temperatures signif-icantly. Therefore, this study attempts to demonstrate that boot-shaped LIVC can be an alternative solution to improve exhaust temperatures above 250oC at low-loaded operations of automotive vehicles.A 1-D engine simulation program is used to model the diesel engine system operating at 1200 RPM engine speed and at 2.5 bar brake mean effective pres-sure (BMEP) engine load. Boot-shaped LIVC is achieved via keeping the valve lift constant (at 4.0 mm) for a while during closure and then closing it at different closure angles. The method results in up to 55oC exhaust temperature rise through reduced in-cylinder airflow and thus, is adequate to keep EAT system above 250oC at low loads. The longer the boot is kept during closure, the lower the air-to-fuel ratio is reduced and the higher the exhaust temperature flows at turbine exit. Similar to conventional LIVC, boot-shaped LIVC improves fuel con-sumption as pumping losses are decreased in the system. Despite aforementioned improvements, EAT warm-up is affected negatively due to the significant drop-off on exhaust mass flow rates. The need to modify only some parts of the lift profile is a technical advantage and can reduce production costs.

The Effect of Injection Parameters on Fuel Consumption and Emissions in A PFI Small Spark Ignition Engine

Mixture formation in port fuel spark ignition engines is one of the most im-portant parameters, which affect combustion and emissions. In this study, the ef-fects of different injection start timings and some other port fuel injection (PFI) parameters on the performance and emissions of a water cooled and single cylin-der spark ignition engine were examined experimentally. The experiments were performed at different engine speeds (1200 and 1500 rpm for effect of injection pressure and 1500 rpm for changing injection timings) and different engine loads (3 bar and 5 bar for injection pressure and 1 bar and 5 bar for start of injection). The start of injection was chosen according to intake pressure measurements. The experiment results showed that brake specific fuel consumption (BSFC) and total hydrocarbon (THC) emissions are increased by the increase of the injection pressure. Because with the increase of injection pressure, the fuel can reach the intake manifold wall or intake valve. Therefore, the fuel enters the cylinder as a droplet. Different start of injection experiments showed that injection times have an effect on emissions and performance. The minimum brake specific fuel con-sumption and THC values were obtained at -243 °CA value of injection start. The twice injection in one cycle increased brake specific fuel consumption and THC emissions.

Introductory measurements of in-cylinder flow past intake valve ports with a film split-fiber probe

A new steady flow test bench test facility has been designed and fabricated for exploration of complex three-dimensional flowfields inside a cylinder of an internal combustion engine. An engine cylinder head of a currently produced car engine with four head valves is utilized as an inlet section of the newly built test bench test. No piston is located in the cylinder and the intake valves are not periodically operated. They remain open during the test periods. An extensive set of initial experimental data has been acquired for both open intake valves and for the location of the probes at two different axial stations in the engine cylinder. The experimental technique of thermo-anemometer split-fiber probes is employed in this research work, which is a novelty never applied before to this class of flows. The probe properties are explained in the paper with emphasis on the probe directional characteristics. The verification tests proved the operational readiness of the new test bench to acquire reliable experimental data at a range of flow conditions simulating real engine settings. The acquired data set base will be used for validations of improved CFD engine design codes. An analysis of the initial set of experimental data clearly indicates that two vortices, or more likely down-flowing spiral flow structures. are present side by side in the cylinder. Mutual interaction of these two flow structures and the ability to generate faithful numerical simulation of this flow pattern for additional planes of measurement and various valve openings will be reported separately.

Effect of injection timing on combustion and IMEP variation of a bi‐fuel compressed natural gas SI engine

AbstractCompressed natural gas (CNG) is a gaseous fuel stored under high pressure in a cylindrical tank. When the CNG is injected into the intake manifold, it expands in the manifold and displaces the air which reduces the volumetric efficiency of the engine. Thus, the corresponding overall energy inside the combustion chamber is also reduced, resulting in reduced power output. CNG injection timing with respect to intake valve opening and closing can be optimized to minimize the losses in volumetric efficiency loss and hence, the power output of the engine. In this study, the combustion instability of the CNG fueled engine has been studied under low throttle condition and compared with gasoline. A comparative investigation of the effects of the start of injection (SOI) timing on combustion stability was conducted on a single‐cylinder spark‐ignition (SI) engine fuelled with gasoline and CNG at 25% throttle opening condition. The ignition timing was kept fixed at 35°, and 40° CA bTDC for gasoline and CNG, respectively, and the SOI timing was varied from 240° CA bTDC to 100° CA aTDC of the intake stroke. The results indicated that SOI timing significantly affects in‐cylinder air‐fuel mixture formation and combustion stability for gasoline and CNG engine. SOI timing corresponds to the closed valve period, shows the higher fluctuation in combustion for gasoline compared to CNG. CNG shows lower fluctuation throughout SOI timing due to homogeneous air‐fuel mixture formation. Early SOI timing forms fuel stratification in the intake port and forms a rich air‐fuel mixture, which reduces the net power output of the CNG engine. CNG requires optimum SOI timing for improved combustion compared to gasoline. It reduced the combustion instability and fluctuation in indicated mean effective pressure. The results will benefit the development of a closed‐loop engine control system for a CNG system.

Numerical Prediction of The Gas Flows in a Reciprocating Engine Cylinder during Intake Stoke (1st Report: Inviscid Flow).(Dept.M)

This paper presents a method for predicting the in-cylinder gas flows during the intake stroke of four-stroke engines. A simplified engine model with a deep-bowl piston configuration, and a central intake valve was used. An inviscid two-dimensional axisymmetric flow was investigated. The model used a finite difference procedure with an expanding/contracting grid in axisymmetric representation. The major source of troubles for the convergence of the solution was the unsteady turbulent jet flow issuing from the intake valve which required very small time intervals for the solution compared with that during the compression stroke where there is no jet flow exists. Results show a complicated flow field during the intake stroke in engine like-geometries.

Open Dual Cycle with Composition Change and Limited Pressure for Prediction of Miller Engines Performance and Its Turbine Temperature

An improved thermodynamic open Dual cycle is proposed to simulate the working of internal combustion engines. It covers both spark ignition and Diesel types through a sequential heat release. This study proposes a procedure that includes (i) the composition change caused by internal combustion, (ii) the temperature excursions, (iii) the combustion efficiency, (iv) heat and pressure losses, and (v) the intake valve timing, following well-established methodologies. The result leads to simple analytical expressions, valid for portable models, optimization studies, engine transformations, and teaching. The proposed simplified model also provides the working gas properties and the amount of trapped mass in the cylinder resulting from the exhaust and intake processes. This allows us to yield explicit equations for cycle work and efficiency, as well as exhaust temperature for turbocharging. The model covers Atkinson and Miller cycles as particular cases and can include irreversibilities in compression, expansion, intake, and exhaust. Results are consistent with the real influence of the fuel-air ratio, overcoming limitations of standard air cycles without the complex calculation of fuel-air cycles. It includes Exhaust Gas Recirculation, EGR, external irreversibilities, and contemporary high-efficiency and low-polluting technologies. Correlations for heat ratio γ are given, including renewable fuels.

Performance and emissions of natural gas/diesel dual-fuel engine at low load conditions: Effect of natural gas split injection strategy

The combination of diesel and natural gas fuels has superior performance in terms of nitrogen oxides (NOx) and particulate matter (PM) emissions when compared to conventional diesel engine. However, this advantage does not hold at low load operating conditions as indicated thermal efficiency (ITE), carbon monoxides (CO), and unburned hydrocarbon (HC) emissions deteriorate. Most published studies tried to resolve this drawback using diesel split injection. However, the present study evaluates natural gas split injection strategy as an alternative to improve the performance and emissions of diesel/natural gas dual-fuel engines at low load conditions. The results show that natural gas split injection with proportional split injection ratio (ISR) and small dwelling timing improves NOx, CO, and HC emissions. Moreover, split injection of natural gas with proportional ISR after intake valve closing (IVC) is found to improve SFC, ITE, and power. Conversely, natural gas split injection strategy with proportional ISR after intake valve opening (IVO) yields poor engine performance. Overall, split injection of natural gas with low ISR yields the greatest engine performance at long dwelling time, whereas it worsens emissions compared to single injection of natural gas at 560°CA ATDC, which serves as the baseline condition. However, very low CO and HC emissions of natural gas split injection is achieved at low ISR and short dwelling time. Finally, this study reveals also that stratification of air/natural gas mixture due to natural gas split injection strategy can significantly improve the performance and emissions of dual-fuel diesel/natural gas engine at low load conditions.

Evolution of methods applied for assessing harmful engine deposits caused by gasoline combustion

The article describes the threat posed by deposits harmful to the proper functioning of spark ignition engines. The areas of indirect and direct injection engines where the most dangerous deposits form are indicated. The factors having significant influence on the occurrence of this unfavourable phenomenon were collected and analyzed. Consequently, a simplified classification of factors influencing the formation of harmful deposits in direct and indirect injection spark ignition engines was made. In the research part of the project, a comparative study of the tendency of gasolines of different composition and physicochemical properties to form deposits was carried out. The criterion for evaluating the detergent properties of gasolines was the tendency to form deposits on intake valves in the case of indirect injection engine and on the injector in the case of direct injection engine. For this purpose, the previously widely used test procedure CEC F-05-93 relating to deposits formed on intake valves in SI indirect injection engines and the latest test procedure CEC F-113-KC relating to the most harmful deposits formed in injectors of DISI (Direct Injection Spark Ignition) engines were used. The purpose of the comparative study conducted was to determine if there was any relatively simple, identifiable relationship between the results of gasoline detergent property evaluations obtained at engine test sites differing in test engine generations, methods of conducting the evaluations, and type of engine deposits formed. As a result, no correlations were found between the testable engine sludge tendency results obtained from tests using the CEC F-05-93 and CEC F-113-KC procedures. Therefore, knowing the evaluation of gasoline conducted according to one of the above mentioned test procedures, one cannot conclude, predict or estimate the evaluation that will be obtained according to the other test procedure. Therefore, the results obtained according to one of the procedures do not allow extrapolation and evaluation of gasoline in terms of tendency to form harmful engine deposits according to the other procedure.

Multi-objective Optimization of Intake Pipe and Valve Timing Based on Improved NSGA-II

The current research is based on a high-speed gasoline engine. The influence of intake pipe structural parameters and valve timing on engine’s performance was analysed by establishing thermodynamic model through software GT-Power. Full factorial experimental design was adopted and moving least squares method to establish response surface model at the full-load speed of 5500 r/min. Multi-objective optimization is carried out with genetic algorithm to solve Pareto frontier curve of economic and dynamic performance. The optimization effect by simulation was verified afterwards. The optimization can serve as guidance to determine valve timing of the fully variable valve and intake pipe. Optimization method proposed to this paper provides control parameters and theoretical basis for fully variable valve and intake pipe, reduces experimental workload and improves development efficiency.

Practical Aspects of Cylinder Deactivation and Reactivation

Cylinder deactivation is an effective measure to reduce the fuel consumption of internal combustion engines. This paper deals with several practical aspects of switching from conventional operation to operation with deactivated cylinders, i.e., gas spring operation with closed intake and exhaust valves. The focus of this paper lies on one particular quantity-controlled stoichiometrically-operated engine where the load is controlled using the valve timing. Nevertheless, the main results are transferable to other engines and engine types, including quality-controlled engines. The first aspect of this paper is an analysis of the transition from fired to gas spring operation, and vice versa, as well as the gas spring operation itself. This is essential for mode changes, such as cylinder deactivation or skip-firing operation. Simulation results show that optimizing the valve timing in the last cycle before deactivating/first cycle after reactivating a cylinder, respectively, is advantageous. We further show that steady-state gas spring operation is reached after approximately 6 s regardless of the initial conditions and the engine speed. The second aspect of this paper experimentally verifies the advantage of optimized valve timings. Furthermore, we show measurements that demonstrate the occurrence of an unavoidable torque ripple, especially when the transition to and from the deactivated cylinder operation is performed too quickly. We also confirm with our experiments that a more gradual mode transition reduces the torque drop.