Spark Timing Research Articles

Effects of high pressure and high-low pressure EGR strategies on the knock tendency, combustion, and performance of a stoichiometric operation natural gas engine

EGR strategies play an important role in improving the combustion and performance of a stoichiometric operation natural gas engine. Based on the numerical simulation and experimental validation, the effects of two EGR strategies, namely high pressure (HP) EGR and high-low pressure (HLP) EGR on the combustion behavior and knock tendency of a natural gas engine were investigated. The optimal EGR rates and spark timings under different full load conditions were obtained, and the reason of the HLP EGR strategy in improving fuel economy was quantitatively evaluated. The simulation results showed that compared with the HP EGR strategy, the optimal EGR rates are reduced and the optimal spark timings are delayed for the HLP EGR strategy. This is due to that the lower boost pressure makes it unnecessary for the HLP EGR strategy to adopt higher EGR rates to suppress knock. Meanwhile, the HLP EGR strategy shortens the flame development period and rapid combustion duration, makes the center of heat release rate curve closer to TDC, increases the peak values of in-cylinder pressure and heat release rate, and significantly reduces the pumping losses. As a result, the HLP EGR strategy increases the indicated thermal efficiency by 3.4% − 7.3%. The dyno experiment of the natural gas engine with the optimized EGR rates and spark timings showed that compared with the HP EGR strategy, the HLP EGR strategy reduces the specific gas consumption by 5.82% − 8.83%. The engine energy balance analysis showed that the in-cylinder heat-transfer losses and exhaust energy for the HLP EGR strategy are reduced, contributing to the fuel saving rates by 2.18% − 2.47% and 4.02% − 6.91%, respectively. While the friction losses are increased, resulting in the reduction in the fuel saving rates by −0.38% to −0.55%. Therefore, the reduction of exhaust energy is the most important fuel saving factor for the HLP EGR strategy.

Hydrogen production in ammonia-fueled spark ignition engines

Anhydrous ammonia (NH3) is a promising carbon-free fuel for internal combustion engines (ICEs) that can be generated from renewable energy sources and stored at high energy density. Ammonia is typically mixed with a small fraction of hydrogen (H2), which serves as combustion promoter to achieve stable combustion over a large range of engine operation. To overcome the difficulties of storing hydrogen, ammonia can be converted to hydrogen onboard by means of a catalytic reactor fed by waste thermal energy from the engine exhaust or by partial oxidation. This work explores an alternative method of producing hydrogen by partial oxidation of fuel-rich ammonia–air mixtures to hydrogen in an engine cylinder while generating useful work. Such an approach eliminates the need for costly catalyst materials and poses the possibility of a dedicated reforming cylinder to provide hydrogen for other cylinders in a multi-cylinder engine. Experiments were conducted in a single-cylinder spark-ignition (SI) engine with parametric sweeps of intake temperature, intake pressure, equivalence ratio, and spark timing. Experimental results show that 6% exhaust gas hydrogen concentration is attainable and 40% of the unburned fuel energy can take the form of hydrogen. Rich equivalence ratios produced higher concentrations of hydrogen and elevated intake temperatures extended the rich stable-operation limit of the engine. Low order chemical modeling yields insights into hydrogen production throughout the engine cycle, revealing that initial consumption of ammonia is advanced of hydrogen production and that competing elementary reactions for the formation and destruction of hydrogen drive its net quantity in the exhaust.

Effects of injection and spark timings on combustion, performance and emissions (regulated and unregulated) characteristics in a direct injection methanol engine

Methanol is a promising low-carbon fuel for internal combustion engines. Increasing the compression ratio combined with direct injection (DI) is an important technology to realize methanol's potential for carbon reduction. In this work, experimental investigations into the effects of injection timing and spark timing (ST) on combustion, performance, and emissions characteristics were carried out on a high compression ratio DI SI methanol engine. The experiments were performed at two intake pressure of 65 kPa and 87 kPa and a constant engine speed of 1500 rpm. The ignition delay and burn duration were slightly reduced with retarding SOI. However, the volumetric efficiency and combustion efficiency decreased rapidly with retarding SOI. The trade-off relation between the effect of SOI on NO and CO emissions was notable. However, methanol and formaldehyde emissions increased simultaneously with retarding SOI. ST retarding could mitigate the NO and CO emissions at the expense of deterioration in heat release rate, thermal efficiency, methanol and formaldehyde emissions. Overall, the combustion stability was good with all SOIs and STs but the combustion efficiency and emissions deteriorated with retarding SOI. A range of −270 to −240 °CA aTDC would be optimal for SOI to obtain good performance.

Study of direct water injection on knock suppressing and engine performance of a gasoline engine

Turbocharger technology has become an essential method for the internal combustion engine to improve fuel economy. However, too high a boost pressure leads to too high a temperature in the combustion chamber at the end of the compression stroke, which can cause knocking or worsen abnormal combustion. Water injection technology plays a role in cooling the intake air and components in the cylinder, which can control the combustion process and suppress knock. This work focused on the influence of direct water injection (DWI) on knock suppression and efficiency improvement using a small turbocharged gasoline engine, investigating the fuel-saving potential of DWI and the optimal strategy of DWI for different engine operating conditions. Taking knock intensity (KI) as the evaluation index, KI decreases from 0.052 to 0.04 MPa, and knock limit spark angle (KLSA) increases with increasing water injection. This work shows that the DWI strategy plays a critical role in earlier spark timing, optimized combustion phase, and improved efficiency. Fuel consumption decreases by 11.55% with the optimal DWI strategy at an operating condition of 2000 rpm and a brake mean effective pressure (BMEP) of 1.3 MPa. Moreover, the optimal water injection timing is at −180°CA under various engine loads. Due to the stronger knock tendency under higher load conditions, the knock suppression is less effective for the same amount of water, so more water injection mass is necessary for higher efficiency.

Review on performance and emission of spark ignition engine using exhaust gas recirculation

ABSTRACT Modernizing electronic control and developing new exhaust gas recirculation (EGR) valves have made it possible to improve EGR accuracy and shorten transient response times. With this paper, we have outlined the findings of research on the effects of various EGR ratios on engine emissions, knock suppression, and charge combustion. Results from experiments conducted by many researchers are summed up as 15% − 18% EGR is found to successfully reduce NOx emissions without impacting engine performance. Because exhaust fumes dilute the fuel/air mixture, this can lead to inefficient combustion, which can lower brake thermal efficiency. According to the findings, selecting the right EGR ratio and spark timing is essential for maximizing engine performance. examined how cold EGR affected knock intensity. It was found that the maximum compression temperature decreased in range of 30–40 kelvin and the cylinder pressure decreased up to 0.4 bar as the EGR increased from 7 to 13%. This demonstrated that the knock was effectively repressed. Because of a buildup of carbon deposits, the EGR valve frequently sticks. In addition to higher fuel consumption or poorer performance, clogged EGRs frequently result in black smoke coming from the exhaust.

Effect of spark timing on the pre-chamber jet ignition in a lean-burn natural gas engine

An enhanced combustion concept, pre-chamber jet ignition can provide high ignition energy and a wide dispersion of ignition sources, thus improving combustion performance and realizing stable lean combustion. However, the ignition performance of the pre-chamber jets depends strongly on the pre-chamber combustion process and is sensitive to many factors. Therefore, this paper will explore the impact of spark timing on the pre-chamber combustion, turbulent jet characteristics, and main chamber combustion performance by CFD simulation based on an active pre-chamber natural gas engine. The in-cylinder flow and combustion processes of the engine are calculated with the fuel-air equivalence ratio of the main chamber maintained at 0.5, and the spark timing varied from 684°CA to 708°CA with a step of 3°CA (compression top dead center is 720°CA). The results show that, in the present engine operating point, the pre-chamber combustion heat release rate is improved when the spark timing is retarded from 696°CA to 705°CA, and the injection velocity of the pre-chamber jet accordingly increases. As the spark timing continues to be delayed until 708°CA, the pre-chamber combustion deteriorates, and the injection velocity of the pre-chamber jet decreases. Under the combustion phase CA50 no more than 725°CA and the combustion duration CA5-90 fixed around 30°CA, the IMEP will maintain a relatively stable value when the spark timing is delayed from 693°CA to 705°CA, in the meantime, the NOx emission decreases with the delay of spark timing. Therefore, on the premise of ensuring engine power performance, it is a feasible scheme to delay spark timing to reduce NOx emission for the natural gas engine with an active pre-chamber.

Experimental investigation on effect of misfire and postfire on backfire in a hydrogen fuelled automotive spark ignition engine

This study investigates the effect of misfire and postfire on backfire in a hydrogen-fuelled automotive spark ignition engine. Backfire is a preignition phenomenon and the flame propagates toward the engine's intake manifold during the suction stroke. Postfire is a post-ignition phenomenon occurring in the exhaust manifold during the exhaust stroke and the flame propagates towards the exhaust manifold or backflow to the combustion chamber or combined both. Misfire occurs when cranking the engine (starting), fouled spark plug, and unoptimized spark timing. Several misfire cycles lead to an increase in the accumulation of unburnt hydrogen-air charge inside the cylinder and 13% hydrogen leaves the exhaust manifold resulting in postfire occurrence in a subsequent cycle. The postfire in the current cycle acting as an external ignition source for the preignition of the accumulated hydrogen-air charge results in backfire in the immediate next cycle. The misfire, postfire and backfire stall the engine operation due to a drop in indicated mean effective pressure. The experimental data indicates the backfire limiting equivalence ratio (BLER) should decrease with an increase in the engine speed as the equivalence ratio varies from 0.91 at 2000 rpm to 0.4 at 4900 rpm. As too advancement of spark timing increases the probability of misfire leading to postfire and backfire, the engine must be operated at backfire limiting spark timing to avoid misfire, postfire, and backfire occurrence. An important point emerged from this study that misfire without postfire does not lead to backfire occurrence. Physical mechanisms and mitigative measures for misfire, postfire and backfire are discussed in detail.

Normal and knocking combustion of hydrogen: A numerical study

This work presents a numerical study of normal and knocking combustion of hydrogen in a cooperative fuel research (CFR) engine. It is noteworthy that this study is the first to simulate this problem in a CFR engine. This engine has a significant relevance to spark-ignition engines as it is used to examine knock susceptibility of different fuels and explore fuel-engine interactions under a controlled environment. Using the Reynolds Averaged Navier Stokes (RANS) framework, a single compression ratio and four different spark timings are considered to investigate the transition from normal to knocking combustion. The results are validated against the experimental pressure trace data for both normal and knocking combustion. The model has been rigorously validated without changing the model constants across all cases. It is shown that for knocking cases an initial auto-ignition hotspot appears near the exhaust valve, where the unburned temperature is higher than the rest of the domain. A pressure wave then propagates, forming a secondary auto-ignition spot and two auto-ignitive flames eventually merge. The propagation speed of the auto-ignitive flame front is found to be 6–10 times higher than that of the premixed flame. Using the resonance theory of Bradley, the auto-ignition events are found to be in the developing detonation region. Furthermore, zero-dimensional homogeneous reactor simulations are shown to be suitable to predict the occurrence of auto-ignition in such engine, while 3-D RANS results are needed to accurately predict the pressure trace and auto-ignition timing. The results of this work also demonstrate how temperature stratification impacts the auto-ignition events.

Precise Internal Turning of Axi-symmetric SS316 Thin-walled Component: Experimentations on ED-Machining Setup

ABSTRACT Axis-symmetric thin-walled cylindrical components like couplers and concentric reducers are needed in mechanical assemblies. These components do not have enough rigidity to hold in the chuck for conventional machining. It is difficult to control their radial dimensions accurately and cost-effectively. In this work, an attempt is made to enlarge the diameter of axis-symmetric thin-walled cylindrical components. Electric discharge machining (EDM) with a centreless turning attachment is utilised. Three variables were selected as input variables: impulse current (IP), pulse on time (Ton), and pulse off count (Toff count). Workpiece RPM, electrode gap, spark, lift, and machining time were constant parameters. Response surface methodology (RSM) was used in planning the experiments. The response variables were material removal rate (MRR), enlargement in diameter (EN), and circularity (Cir). It was found that MRR and EN increase with the increase in IP and Ton and decrease with the rise in Toff time. The values of optimum process parameters found at impulse current (15 A), pulse on time (490 µs) and pulse off count (6) were MRR (366 mg/min), enlargement in diameter (229 µm) and circularity (0.014 µm). Moreover, the sample’s topography changed as hardness and corrosion resistance increased.

Modelling the Impacts of Hydrogen–Methane Blend Fuels on a Stationary Power Generation Engine

To reduce greenhouse gas emissions from natural gas use, utilities are investigating the potential of adding hydrogen to their distribution grids. This will reduce the carbon dioxide emissions from grid-connected engines used for stationary power generation, and it may also impact their power output and efficiency. Promisingly, hydrogen and natural gas mixtures have shown encouraging results regarding engine power output, pollutant emissions, and thermal efficiency in well-controlled on-road vehicle applications. This work investigates the effects of adding hydrogen to the natural gas fuel for a lean-burn spark-ignited four-stroke, 8.9 liter eight-cylinder naturally aspirated engine used in a commercial stationary power generation application via an engine model developed in the GT-SUITETM modelling environment. The model was validated for fuel consumption, air flow, and exhaust temperature at two operating modes. The focus of the work was to assess the sensitivity of the engine’s power output, brake thermal efficiency, and pollutant emissions to blends of methane with 0–30% (by volume) hydrogen. Without adjusting for the change in fuel energy, the engine power output dropped by approximately 23% when methane was mixed with 30% by volume hydrogen. It was found that increasing the fueling rate to maintain a constant equivalence ratio prevented this drop in power and reduced carbon dioxide emissions by almost 4.5%. In addition, optimizing the spark timing could partially offset the increases in in-cylinder burned and unburned gas temperatures and in-cylinder pressures that resulted from the faster combustion rates when hydrogen was added to the natural gas. Understanding the effect of fuel change in existing systems can provide insight on utilizing hydrogen and natural gas mixtures as the primary fuel without the need for major changes in the engine.

A Preliminary Study of Spark-Ignition System for Free-Piston Linear Engine

In recent years, the free-piston linear engine (FPLE) has attracted increasing interest from researchers worldwide. With the development of computer control technology, internal combustion engine technology, and material science, there have been significant advances in the aspects of FPLE simulation, experimental techniques, as well as systems FPLE control. This paper presents a model of a two-stroke, spark-ignition free-piston engine converted from two small two-stroke engines. It has a bore size of 34 mm and a maximum stroke of 28 mm. The linear engine uses gasoline fuel that is available on the market. The purposes of the research show a model of the starting system, investigation the effects of spark timing, and effective pressure. A premixed air-fuel charge is conducted by a carburetor then it is directly supplied into each cylinder. The spark timing was varied at 1 mm and 2 mm away from the maximum top dead center with the speed starting at 10 Hz. The model successfully ignited with a maximum pressure of 7.5 kg/cm2 at the ignition of 1 mm before top dead center (TDC) and 9.5 kg/cm2 at the ignition of 2 mm before TDC. The research has completed the initial intentions such as a theoretical investigation, calculation, determination of the engine model, and starting mechanism. Preliminary results have confirmed the feasibility of proposing the FPLE model.

Effects of knock intensity measurement technique and fuel chemical composition on the research octane number (RON) of FACE gasolines: Part 2 – Effects of spark timing

The Research and Motor Octane Number (RON, MON) characterize a fuel’s knock resistance by rating the knock intensity of a sample fuel relative to that of Primary Reference Fuels (PRF) in a Cooperative Fuel Research (CFR) Engine. A fuel’s octane number is regulated to prevent damage from autoignition leading to knocking combustion in spark-ignition engines. The operational differences between the standard RON rating and modern engine operation are explored in a three-part publication series. The previous study focused on the effects of lambda and knock characterization. This second study primarily focuses on the effects of spark timing on RON determination. Following the findings from the first publication, the knock intensity was captured by the knockmeter and by the maximum amplitude of pressure oscillations (MAPO) at the lambda of peak knock intensity and stoichiometry. Knock-limited spark advance tests were conducted for a set of seven Fuels for Advanced Combustion Engines (FACE) from the Coordinating Research Council (CRC) with varying chemical composition, PRFs, and Toluene Standardization Fuels (TSFs). For retarded spark timings, pre-spark low-temperature heat release was found for low RON PRFs. Low RON PRFs also showed knocking characteristics before reaching the center of combustion suggesting that the use of knock-limited spark advance (KLSA) was preferred over the knock-limited combustion phasing. Primarily paraffinic fuels tended towards increased pressure oscillations while dominantly aromatic fuels experienced higher pressure rise rates. A MAPO-based KLSA correlated best to Octane Index at a negative K-factor suggesting beyond RON operation despite being at otherwise RON conditions. At stoichiometry, the MAPO-based KLSA did neither correlate to RON nor Octane Index. Good agreement was found between KLSA-based effective RON from this study to the MAPO-based effective RON from the first study.

Thermal efficiency improvement of a spark ignition engine by stratified water distribution

The stratified water distribution was introduced on a single cylinder direct injection spark ignition engine by changing the direct Water Injection Timing (WIT) and Water Fuel Ratio (WFR) to control the water distribution states before ignition. Experiments were conducted to fundamentally understand the stratified water effects on combustion process control. The results show that different water injection timing could result in wall wetting state, homogeneous state, and stratified state. Stratified water distribution has more obvious suppression effects on knock combustion than other states. Furthermore, optimized combustion process of stratified water distribution case by advancing spark timing is with higher thermal efficiency than homogeneous case.Finally, with the experiment of increasing water injection amounts at stratified state, thermal efficiency increasing was realized by 2.1 %. The high correlation between ignition delay and knocking combustion was demonstrated, which substantiate that water stratified injection has much talent on knock combustion suppressing and thermal efficiency increasing. In further research, the stratified water effects by split injection strategy is hopeful to reduce the water amounts and avoiding oil dilution.

Knock probability determination in a turbocharged gasoline engine through exhaust gas temperature and artificial neural network

In the present study, a new combination of different available engine sensors along with an exhaust gas temperature sensor is used as the input of an artificial neural network to recognize knock incidents probability. In this regard, comprehensive experimental test trips on a turbocharged gasoline-powered vehicle are defined, and about 5 million data sets are extracted. These data are filtered, and then the optimization process is conducted on the network to minimize errors in the presented network. The output of the presented network would be the probability of knock occurrence in different operating conditions which a probability of more than 50% would be recognized as a knock occurrence. The results reveal that the neural network can detect knocking by traditional engine sensors plus exhaust gas temperature sensors with 92% precision. The exhaust gas temperature increases in most knock occurrences due to spark time retarding. The network reveals the little effect of the air temperature sensor on knock incidence, while the strong correlation of intake manifold pressure on the knock occurrence is shown. The spark timing, engine speed, intake temperature, and pressure sensor have the most considerable effect on knock detection, while the camshaft angle sensor has an almost negligible effect on knock detection. The current network promotes knock detection methods by introducing the knock probability, and additional improvement on the presented method can lead to a reliable procedure for knock detection.

Numerical investigation of a large bore, direct injection, spark ignition, hydrogen-fuelled engine

This paper presents Unsteady Reynolds Averaged Navier Stokes (URANS) simulations of a large bore, hydrogen-fuelled direct injection spark ignition (DISI) engine at different spark and start of injection (SOI) timings. Six cases are simulated, including three with various spark timings at a low boost level and three with advanced to late injection timings at a higher boost level. The numerical simulations are validated with experimental data for four out of six cases, while the other two are considered blind computational fluid dynamics (CFD) simulations. It is shown that the autoignition occurs with advanced spark timing due to high in-cylinder pressure and unburnt temperature. For different SOIs, it is demonstrated that flame propagation involves a spark-initiated flame combined with an autoignition generated flame. The case with the late injection timing features poor mixing and slower combustion due to the presence of lean mixtures near the spark plug. As a result, this case features the lowest thermal efficiency when SOI is varied. In all cases, both mixture and temperature stratification are present. Simulations of zero-dimensional chemical reactors demonstrate that this stratification must be correctly captured for accurate prediction of autoignition timing.

ZnO quantum dots decorated carbon nanotubes-based sensors for methanol detection at room temperature

In this work, a highly sensitive methanol gas sensor at room temperature is reported based on ZnO quantum dots (QDs) decorated carbon nanotubes (CNTs) systesized via thermal vapor deposition process following by metal sparking technique with varying sparking times. The FE-SEM, TEM and XPS characterizations confirm a high quality of ZnO QDs decoration (average particle size of ~2.5 nm) on CNTs surfaces (average diameter of ~30 nm). The gas-sensing results show that the ZnO QDs decorated CNTs with the sparking time of 30 s own the highest response to methanol compared with those of other the sparking times and undecorated one as well as high selectivity to methanol against acetone, ammonia, dimethylformamide, ethanol, formaldehyde and toluene at room temperature. The methanol-sensing mechanism of ZnO QDs decorated CNTs sensor can be discussed based on the low-temperature reducing reaction process enhanced via CNTs-ZnO QDs (p-n) heterojunctions and quantum-size effects.

Low thermal inertia thermal barrier coatings for spark ignition engines: An experimental study

Application of thermal barrier coatings in spark ignition engines have historically been avoided due to the knock penalty associated with higher surface temperatures induced by the ceramic layer. However, advances in low thermal inertia coatings (i.e. temperature swing coatings) that combine low thermal conductivity with low volumetric heat capacity can prevent excessively high surface temperatures during the intake stroke and reduce or avoid knock while improving performance and efficiency. In this study, a novel coating material was tested in a low compression ratio spark ignition engine to evaluate the performance of an advanced low thermal inertia coating during steady and cold-start conditions. A total of four pistons with this novel material was tested, with an additional piston coated with gadolinium zirconate. Spark timing sweeps demonstrated a maximum 0.8% relative thermal efficiency gain with a thin coating of the novel material. The novel material coated above 200-microns showed a deterioration in performance and efficiency due to charge heating increasing knock propensity. Cold-start tests demonstrated that charge heating is beneficial for reducing unburned hydrocarbons and particle matter emissions.

Direct Numerical Simulation of Partial Fuel Stratification Assisted Lean Premixed Combustion for Assessment of Hybrid G-Equation/Well-Stirred Reactor Model

Abstract Partial fuel stratification (PFS) is a promising fuel injection strategy to stabilize lean premixed combustion in spark-ignition (SI) engines. PFS creates a locally stratified mixture by injecting a fraction of the fuel, just before spark timing, into the engine cylinder containing homogeneous lean fuel/air mixture. This locally stratified mixture, when ignited, results in complex flame structure and propagation modes similar to partially premixed flames and allows for faster and more stable flame propagation than a homogeneous lean mixture. This study focuses on understanding the detailed flame structures associated with PFS-assisted lean premixed combustion. First, a two-dimensional direct numerical simulation (DNS) is performed using detailed fuel chemistry, experimental pressure trace, and realistic initial conditions mapped from a prior engine large-eddy simulation (LES), replicating practical lean SI operating conditions. DNS results suggest that the conventional triple flame structure is prevalent during the initial stage of flame kernel growth. Both premixed and nonpremixed combustion modes are present with the premixed mode contributing dominantly to the total heat release. Detailed analysis further reveals the effects of flame stretch and fuel pyrolysis on flame displacement speed. Based on the DNS findings, the accuracy of a hybrid G-equation/well-stirred reactor (WSR) combustion model is assessed for the PFS-assisted lean operation in the LES context. It is found that the G-equation model qualitatively captures the premixed branches of the triple flame, while the WSR model predicts the nonpremixed branch of the triple flame. Finally, potential needs for improvements to the hybrid G-equation/WSR modeling approach are discussed.

Numerical Optimization of Spray-Guided Spark Assistance for Cold Idle Operation in a Heavy-Duty Gasoline Compression Ignition Engine

This article describes the results of a response surface model (RSM)-based numerical optimization campaign for spray-guided spark assistance at cold operations in a heavy-duty gasoline compression ignition (GCI) engine. On the basis of an earlier work on spark-assisted GCI cold combustion, a space-filling design of experiments (DoE) method was first undertaken to investigate a multitude of hardware design variables and engine operating parameters. The main design variables included the number of injector nozzles, fuel split quantities and injection timings, and spark timing. The objective variables were engine combustion efficiency (ŋc), maximum pressure rise rate (MPRR), and engine-out nitrogen oxide (NOx) emissions. A total of 150 design candidates were automatically generated using the Sobol sequence method provided by the commercial software package, CAESES. Then, closed-cycle computational fluid dynamic (CFD) spark-assisted GCI simulations under cold idling operations were performed. The outcomes from the CFD-DoE design campaign were utilized to construct high-fidelity RSMs that allowed for further design optimization of the spark plug- and fuel injector-related design variables, along with fuel injection strategy parameters. A merit function with respect to objective variables was formulated with an appropriate weight assignment on each objective variable. Finally, the best design candidate was identified from the RSM-based optimization process and further validated in the CFD analysis. The best design candidate showed the potential to significantly improve combustion efficiency (ŋc > 90%) over the baseline at cold idle while satisfying MPRR and NOx emissions constraints (MPRR < 5 bar/CAD and NOx < 4.5 g/kWh).

Syngas production from biogas in a polygeneration process: Simultaneous partial oxidation and dry reforming in a piston engine

This work experimentally investigates the fuel-rich combustion of CH4/CO2/O2 mixtures in a piston engine. The focus of the experiments is to determine suitable operating parameters in terms of stable engine operation, syngas production, CO2 conversion, and avoiding soot emissions. In particular, the spark timing, CO2 intake mole fraction, equivalence ratio, and compression ratio were varied. Results show stable spark-ignition operation over a wide range of the investigated parameters at a compression ratio of 10. Acceptable operation could be achieved within the spark timing limits of -38° to 10 °CA after top dead center, 7 to 27% CO2 in the inlet and equivalence ratios from 2 to 2.5. A maximum H2 yield of 62% could be achieved at an equivalence ratio of 1.9 and a CO2 intake mole fraction of 4% at a compression ratio of 4.5. Spark time advancing from -10 to -38 °CA enhanced the dry reforming reaction and increased the hydrogen yield per methane from 38 to 45%. A significant influence of compression ratio on the amount of soot in the product gas was observed, showing that higher compression ratios increase soot formation.