Retarded Spark Timing Research Articles

Influence of steam induction on the performance and hydrogen knock limit of a hydrogen-gasoline spark ignition engine

This study examines the effect of steam induction on the performance and hydrogen knock limit of a hydrogen-gasoline dual-fuel Spark Ignition (SI) engine. The experimental setup includes gasoline direct injection, along with steam and hydrogen port induction. Steam-to-fuel ratios of 7.5 %, 15 %, and 22.5 % were used, and hydrogen was introduced in step sizes of 2 LPM until knock onset. The extension of the hydrogen knock limit was achieved through steam induction and retarding spark timing. Under the default configuration, the maximum achievable hydrogen flow rate was 8 LPM, which increased to 20 LPM with retarded spark timing and 22.5 % steam proportion. Steam induction initially increased and then decreased brake thermal efficiency, brake mean effective pressure, in-cylinder pressure, and heat release rate. In contrast, advancing spark timing and hydrogen enrichment consistently improved performance and combustion characteristics. Cyclic variation showed a decreasing trend with the introduction of steam and hydrogen. Unlike hydrogen enrichment, steam addition reduced CO and NOX emissions.

Influence of ethanol–gasoline–hydrogen and methanol–gasoline–hydrogen blends on the performance and hydrogen knock limit of a lean-burn spark ignition engine

This study investigates the effects of ethanol–gasoline and methanol–gasoline blends on the performance of a lean-burn spark ignition engine and the hydrogen knock limit of the engine with hydrogen-enriched fuel. The experimental setup includes liquid in-cylinder fuel injection and hydrogen port induction. Ethanol and methanol are blended with pure gasoline up to 50% by volume (20%, 35% and 50%) and all fuels are drip-fed with hydrogen until combustion knock is detected in step size of 2LPM. The hydrogen knock limit extension is achieved with ethanol–gasoline and methanol–gasoline blends and is further extended by spark-timing retardation. Retarded spark timing and ethanol–methanol blended fuels reduce the brake thermal efficiency, brake mean effective pressure, and peak in-cylinder pressure. The cyclic variation increases with ethanol and methanol addition and decreases with spark-timing retardation and hydrogen enrichment. Unlike hydrogen enrichment, ethanol and methanol addition reduce the CO2 and NOx emissions but increase the CO emission.

Divided Exhaust Period Assessment for Fuel-Enrichment Reduction in Turbocharged Spark-Ignition Engines

<div>Turbocharged spark-ignition (SI) engines, owing to frequent engine knocking events, utilize retarded spark timing that causes combustion inefficiency, and high turbine inlet temperature (Trb-In T) levels. Fuel enrichment is implemented at high power levels to prevent excessive Trb-In T levels, resulting in an additional fueling penalty and higher CO emissions. In current times, fuel-enrichment reductions are of high strategic importance for engine manufacturers to meet the imminent emissions regulations. To that end, the authors investigated the divided exhaust period (DEP) concept in a 2.2 L turbocharged SI engine with a geometric compression ratio of 14 by decoupling blowdown (BD) and scavenge (SC) events during the exhaust process. Using a validated 1D engine model, the authors first analyzed the DEP concept in terms of pumping mean effective pressure (PMEP) and engine knocking (KI) reduction. Subsequently, the authors examined the effectiveness of the DEP concept using a “low-restriction exhaust flowpath” and varying late intake valve closing (LIVC) duration.</div> <div>First, using DEP, significant PMEP and KI reductions benefits were observed at high power engine conditions along with a large increase in Trb-In T from the early blowdown event. Subsequently, use of a low restriction exhaust flowpath and a shortened LIVC duration further elevated the DEP benefits, including Trb-In T reduction that facilitated enrichment reduction. At 4,000 RPM/20 bar BMEP, ~70% lower PMEP and a 2.2 point increase in ITEg were noted relative to the base engine. However, the 2,000 RPM peak torque engine condition was compromised using DEP, due to knock limitation and deteriorated stock turbocharger performance. Finally, DEP design integrated with an off-the-shelf (new) turbocharger system remedied the low-end torque challenges and demonstrated a notable enrichment reduction and thermal efficiency benefits at the full load engine curve including the 200 kW rated condition.</div>

Hydrocarbon and particulate matter evolution in the exhaust manifold of a spark-ignited engine under cold-start operation

Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon, and particulate matter (PM) emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster three-way catalyst light-off, and engine out emissions during that period. In this study, various exhaust gas and PM species were measured at three locations in the exhaust manifold using advanced hydrocarbon and PM speciation methods in addition to standard exhaust-gas-analyzers to characterize how or if these species evolve downstream of the exhaust port during cold-start operation. A gasoline direct injected spark ignited (DISI) single cylinder engine was run at 2-bar net indicated mean effective pressure (NIMEP) at spark timings ranging from normal-SI operation relevant early spark timing of -10 degrees after top dead center firing (dATDCf) to more cold-start-relevant retarded spark timing of 25dATDCf. At the retarded spark timings, the exhaust manifold gas temperature increased downstream of the exhaust port indicating the presence of oxidation reactions that counteract heat transfer losses; a trend also supported by oxidation of total hydrocarbons (THC), CO, and H2 observed downstream of the exhaust port. Additionally, increase in NOx emissions downstream of the exhaust port indicated presence of high temperature required to drive NOx chemistry. Aromatics were the largest exhaust hydrocarbon species group detected at all spark timings, while the paraffins were under-represented from their fuel composition fraction. Organic carbon accounted for more than 95% of the PM mass at exhaust port for all spark timings. At retarded spark timings, the PM mass reduced downstream of the exhaust port primarily driven by organic carbon oxidation. Particle number and size measurements at retarded spark timings indicated a reduction in particle count downstream of the exhaust port with an accompanying increase in particle size possibly due to agglomeration.

Numerical investigation on combustion system optimization for direct injection of aviation kerosene in a two-stroke SI engine for unmanned aerial vehicle

In recent years, the transition from gasoline to heavy fuel has received more and more attention in the application of unmanned aerial vehicles (UAVs). This study aims to convert a two-stroke port fuel injection (PFI) gasoline engine as the prototype engine to a direct injection (DI) aviation kerosene engine by numerical simulations. The direct-injection combustion system was designed, and then the effects of fuel injection timing and ignition strategy on combustion and knock of a two-stroke direct injection spark-ignition (DISI) engine with aviation kerosene as fuel were evaluated. The results show that the direct-injection combustion system can increase the airflow velocity, thereby accelerating fuel diffusion and flame propagation. The knock intensity (KI) and indicated mean effective pressure (IMEP) all decrease with the retardation of the injection timing and spark timing. Injection timing has a greater impact on IMEP than spark timing. For different injection timings, spark timing has a more obvious impact on KI when injection timing is advanced. The coordinated control strategy of advancing injection timing and retarding spark timing can effectively suppress the tendency of knock and broaden its load range, which can make the power recovery rate reach 88.57% compared to the baseline engine.

Prediction of knock propensity using stochastic modeling in a spark-ignition engine

To comply with stringent CO2 regulations, enhanced thermal efficiency has been prioritized in internal combustion engine development; however, this has strongly driven the development of engines with operating conditions more prone to knock. Current knock sensors have its limitations to decompose knock signal by degradation so that it required a cross-referencing signal. In addition, knock control intervention is currently preceded by the occurrence of the knock, leading to decrease in thermal efficiency by retarding spark timing. In the present work, a novel prediction model for knock propensity (incidence) is presented, aiming to enable active control of knock or autoignition, and to support conventional knock sensor for cross-referencing by facilitating virtual knock sensor. A zero-dimensional model-based prediction of the in-cylinder pressure is demonstrated to prevent using in-cylinder pressure transducer, along with other incorporated predictive sub-models for the residual gas fraction, heat loss, burn duration, and heat release rate. Ignition delay correlation and Livengood-Wu relation are used to predict the onset of knock, and a burn point-based criterion is newly proposed for application in stochastic modeling for determining the knock propensity. The predicted knock propensity from the combined holistic model shows a remarkable agreement with experimental results.

Experimental study of knock combustion and direct injection on knock suppression in a high compression ratio methanol engine

Methanol is a competitive low-carbon fuel for spark ignition engines. Though it has higher knock resistance than gasoline fuel, knocking combustion is still an obstacle for the application of methanol in spark ignition engines with relatively higher compression ratios. In this work, experimental investigations into knocking combustion and suppression were conducted on a single-cylinder, naturally aspirated, SI engine with a compression ratio of 15. Firstly, the knocking characteristics of the methanol engine with stoichiometric mixture under port fuel injection mode were evaluated. Results showed that knocking combustion occurred under medium and high loads. Especially, under the condition of indicated mean effective pressure (IMEP) = 0.7 MPa, some random heavy knock cycles with ultra-high knock intensity were observed. The frequency of heavy knock was 2.5% and the highest maximum amplitude of pressure oscillations reached 2.39 MPa. This heavy knock was similar to the super-knock phenomenon in boosted direct injection gasoline engines, and it can not be eliminated by retarding spark timing or adopting fuel-lean combustion. Then, the mechanism of the heavy knock was studied by thermodynamic condition analysis. Results showed that the heavy knock was triggered by pre-ignition which was induced by some hot spots in the combustion chamber. Finally, to make the best use of the charge cooling effect, the methanol direct injection strategy was applied to suppress the knocking combustion. When the engine worked with full opening throttle and adopt a single injection, the maximum knock intensity decreased to 0.43 MPa×°CA at −350 °CA ATDC start of injection which was 5.1% of the maximum value during port fuel injection mode. With the co-optimization of the start of injection and spark timing, the engine with a stoichiometric mixture could operate within the knock intensity limit at full load. Under this operating condition, the crank angle of 50% mass fraction burned located at 12 °CA ATDC and IMEP = 1.05 MPa was achieved. What’s more, adopting the optimal split injection instead of a single injection, the knock intensity was further reduced by 14.3% with a slight reduction of 0.02 MPa in IMEP.

Numerical Study on the Performance and NOx Emission Characteristics of an 800cc MPI Turbocharged SI Engine

The main purpose of this study is to optimize engine performance and emission characteristics of off-road engines with retarded spark timing compared to MBT by repurposing the existing passenger engine. This study uses a one-dimensional (1D)-simulation to develop a non-road gasoline MPI turbo engine. The SI turbulent flame model of the GT-suite, an operational performance predictable program, presents turbocharger matching and optimal operation design points. To optimize the engine performance, the SI turbulent model uses three operation parameters: spark timing, intake valve overlap, and boost pressure. Spark timing determines the initial state of combustion and thermal efficiency, and is the main variable of the engine. The maximum brake torque (MBT) point can be identified for spark timing, and abnormal combustion phenomena, such as knocking, can be identified. Spark timing is related to engine performance, and emissions of exhaust pollutants are predictable. If the spark timing is set to variables, the engine performance and emissions can be confirmed and predicted. The intake valve overlap can predict the performance and exhaust gas by controlling the airflow and combustion chamber flow, and can control the performance of the engine by controlling the flow in the cylinder. In addition, a criterion can be set to consider the optimum operating point of the non-road vehicle while investigating the performance and exhaust gas emissions accompanying changes in boost pressure With these parameters, the design of experiment (DoE) of the 1D-simulation is performed, and the driving performance and knocking phenomenon for each RPM are predicted during the wide open throttle (WOT) of the gasoline MPI Turbo SI engine. The multi-objective Pareto technique is also used to optimize engine performance and exhaust gas emissions, and to present optimized design points for the target engine, the downsized gasoline MPI Turbo SI engine. The results of the Pareto optimal solution showed a maximum torque increase of 12.78% and a NOx decrease of 54.31%.

The challenges of using detailed chemistry model for simulating direct injection spark ignition engine combustion during cold-start

Computational Fluid Dynamics (CFD) modeling of gasoline spark-ignited engine combustion has been extensively discussed using both detailed chemistry mechanisms (e.g., SAGE) and flamelet models (e.g., the G-equation). The models have been extensively validated under normal operating conditions; however, few studies have discussed the capability of these models in capturing DISI combustion under cold-start conditions. A cold-start differs from normal operating conditions in various respects, such as (1) having highly retarded spark timing to help generate a high heat flux in the exhaust for a rapid catalyst light-off; (2) having split-injection strategies to ensure a favorable stratification at the vicinity of the spark plug and reduced film formation; and (3) having optimized valve timings for reduced NOx emissions via increased internal residuals and reduced hydrocarbon (HC) emissions via prolonged oxidation of the combustion products. The retarded spark timing introduces the adverse effect of a decaying turbulence field, which results in a reduced turbulent flame speed. The analysis of all these factors happening inside the cylinder appears complicated at first glance; however, it could be made possible by efficient use of the existing CFD models. The current study explored the capability of the SAGE detailed chemistry model in capturing cold-start flame travel in a DISI engine. The results were then compared against the G-equation-based GLR model, which has been validated for excellent predictions of the DISI cold-start combustion as shown by Ravindran et al. The flame travel was captured on a Borghi-Peters diagram to find that the flame travels through corrugated, wrinkled, and laminar regimes. In order to fully evaluate the capability of the detailed chemistry model in predicting such changing turbulence-chemistry interactions, it will need to be studied individually in each regime; however, the scope of the current paper is limited to the study of the model behavior in the laminar regime, which will be shown to be important for DISI engine cold-start. The SAGE detailed chemistry model, with a toluene reference fuel (TRF) mechanism validated for gasoline laminar flame speeds, was found to significantly under-predict the flame propagation speeds because of the effects of numerical viscosity and discrepancies in capturing molecular diffusion. The causes and effects of this under-prediction and the ways in which this can be improved are presented in the paper.

Experimental investigation of a heavy-duty natural gas engine performance operated at stoichiometric and lean operations

There is a need for decarbonization in power generation and transportation. Natural gas can replace conventional petroleum fuels due to its low carbon-to-hydrogen ratio, especially in existing diesel engines. This paper was based on the hypothesis that “ideal” natural gas engines would operate both stoichiometric and lean, as needed. Therefore, the need to identify the effect of leaning the mixture on several parameters not usually shown in the literature. This paper compared the performance and emissions of a heavy-duty diesel engine converted to natural gas spark ignition operation under stoichiometric (equivalence ratio, ϕ = 1.0) and lean (ϕ = 0.8) operation. The original cylinder head and piston were maintained, and no exhaust gas recirculation was used. The results showed that lean operation decreased peak cylinder pressure and maximum pressure rise rate by 10–15% and 1 bar/°CA, respectively, and increased the volumetric efficiency from ~72% to ~74%. While it also increased the ignition lag, which translated in up to 5°CA delay in the location of peak pressure and crank angle associated with 50% of energy release at the same spark timing and a ~ 5°CA advance in the location of maximum indicated mean effective pressure, it had a negligible effect on the combustion duration due to distinguishing characteristics of gas and flame motion in the bowl-in-piston chamber. Lean operation increased unburned hydrocarbon and nitrogen oxides emissions by up to 15% and 300%, respectively, and carbon monoxide emissions were ~ 20× lower. Lean operation improved indicated thermal efficiency by two percentage points due to a 15% decrease in the heat losses but decreased the exhaust temperature by ~ 50 °C, which would affect the aftertreatment performance. Stoichiometric operation reduced the combustion fluctuations. However, the increased turbulence inside the “fast-burn” bowl-in-piston chamber compensated for the lower natural gas flame speed, with a variation of the indicated mean effective pressure below 2.5% even at ϕ = 0.8. Finally, important differences were observed compared to a traditional spark ignition engine. For example, diesel engine conversation increased nitrogen oxides emissions under lean burn but lowered unburned hydrocarbon and carbon oxide emissions when retarding spark timing from the optimum value. These findings suggest that more studies are needed to better understand the optimization of dedicated natural gas engines converted from diesel, under both lean and stoichiometric operations.

Effects of engine restart strategy on particle number emissions from a hybrid electric vehicle equipped with a gasoline direct injection engine

Hybrid electric vehicle (HEV) tend to emit large amount of gaseous and particle emissions right after engine restart (ER). In this study, on-board particulate number (PN) measurement test and chassis dynamometer tests were conducted to analyze the effects of the ER combustion strategy on the gaseous and particle emission characteristics of a gasoline direct injection (GDI) HEV. The on-board PN measurement tests were conducted to examine the effect of a parameter sweep such as injection pressure, end of injection (EOI), spark timing of ER. It was measured by the pegasor particle sensor (PPS)-M, a device that measures the number of particles with a size from 23 nm to 25 μm, and the ES-582.1 module that can acquire electronic control unit (ECU) data. In the chassis dynamometer test, particle emissions, gaseous emissions and fuel economy of the reference case and the Combination Case 2 were compared and analyzed in the worldwide harmonized light vehicles test cycles (WLTC) mode test using Horiba, MEXA-ONE and MEXA-2000 solid particle counting system (SPCS). Reference case refers to a control strategy that does not touch anything in the vehicle's basic control strategy, and Combination Case 2 is the largest PN reduction case combined by calibrating the parameters. On-board PN measurement tests show that in reference case, ER PN accounted for about 70% of the total PN. Compared to the reference case, the sum of ER PN averages tended to decrease with higher injection pressure, advanced EOI, and retarded spark timing. The results of Combination Case 2 indicate that the sum of ER PN averages decreased by 88.7% compared to the reference case. In the WLTC mode test, THC, CO emissions and fuel economy were almost the same, and NOx was reduced by 85.6%. In both PPS and SPCS, the sum of ER PN average ratios decreased by 20%.

Combustion and emissions behaviors of a stoichiometric GDI engine with simulated EGR (CO2) at low load and different spark timings

Exhaust gas recirculation (EGR) is one of the most effective measure to control NOX emissions in the engines. CO2 was introduced to intake as simulated EGR (CO2), the combustion and emissions behaviors of a stoichiometric GDI engine with simulated EGR (CO2) at engine speed of 1500 rpm, engine load of 25% and different spark timings were studied experimentally. Experimental results show that EGR and retarded spark timing would slow the combustion. At the same EGR rate, the effect of actual EGR on combustion parameters is much greater than that of simulated EGR (CO2). A large amount of inert gas in EGR will greatly aggravate combustion, leading to increase COVimep. The order of COVimep is actual EGR rate = 15% ≫ simulated EGR (CO2) rate = 15% > EGR rate = 0%. Spark timing has little effect on BSCO and BSHC for with/without EGR at low load. At any constant spark timing, BSCO actural EGR rate = 15% ≫ BSCO simulated EGR (CO2) rate = 15%> BSCO EGR rate = 0%. BSNOX and soot emissions decrease significantly with retarding spark timing for with/without EGR. BSNOX and soot emissions show same tendencies with retarding spark timing and increasing EGR rate. BSNOX emissions is actual EGR > simulated EGR (CO2) ≈ retarded spark timing. At a constant spark timing, soot actual EGR rate = 15%< soot simulated EGR (CO2) rate = 15%< soot EGR rate = 0%. EGR reduces reaction rate of soot formation and rises the oxidation rate of soot.

Improving computational fluid dynamics modeling of Direct Injection Spark Ignition cold-start

Developing a profound understanding of the combustion characteristics of the cold-start phase of a Direct Injection Spark Ignition (DISI) engine is critical to meeting increasingly stringent emissions regulations. Computational Fluid Dynamics (CFD) modeling of gasoline DISI combustion under normal operating conditions has been discussed in detail using both the detailed chemistry approach and flamelet models (e.g. the G-Equation). However, there has been little discussion regarding the capability of the existing models to capture DISI combustion under cold-start conditions. Accurate predictions of cold-start behavior involves the efficient use of multiple models - spray modeling to capture the split injection strategies, models to capture the wall-film interactions, ignition modeling to capture the effects of retarded spark timings, combustion modeling to accurately capture the flame front propagation, and turbulence modeling to capture the effects of decaying turbulent kinetic energy. The retarded spark timing helps to generate high heat flux in the exhaust for the faster catalyst light-off during cold-start. However, the adverse effect is a reduced turbulent flame speed due to decaying turbulent kinetic energy. Accordingly, developing an understanding of the turbulence-chemistry interactions is imperative for accurate modeling of combustion under cold-start conditions. In the present work, combustion characteristics during the cold-start, fast-idle phase is modeled using the G-Equation flamelet model and the RANS turbulence model. The challenges associated with capturing the turbulent-chemistry interactions are explained by tracking the flame front travel along the Borghi-Peters regime diagram. In this study, a modified version of the G-Equation combustion model for capturing cold-start flame travel is presented.

A Comparison Study on Emission Characteristics of Using Higher Alcohol Oxygenates with Gasoline in a Multipoint Fuel Injection Spark-Ignition Engine

Abstract Usage of oxygenates has become common practice for improving gasoline properties. In this study, two oxygenates, one from the ether family (diisopropyl ether (DIPE)) and one from the alcohol family (n-butanol), were mixed with gasoline at 5, 15, and 25 % by volume to get D5, D15, D25, N5, N15, and N25 blends. Blends of DIPE (D5, D15, and D25) and n-butanol (N5, N15, and N25) were tested in a four-stroke four-cylinder multipoint fuel injection spark-ignition engine at 0.33 MPa (brake mean effective pressure) over a speed range of 1,400 to 2,800 r/min with 200 r/min increments. The performance and emission behavior obtained from blends of DIPE and n-butanol were compared with base gasoline. Lower hydrocarbon and carbon monoxide emissions are observed for oxygenate blends than for gasoline. However, blends of DIPE and butanol emitted higher nitrogen oxide (NOx) than gasoline. The retarded spark timing from 14° before top-dead-center (bTDC) to 12° bTDC reduced NOx emissions from blends. The study also concludes that DIPE is a suitable and comparable oxygenate additive to n-butanol and offers high knock resistance equal to n-butanol.

In-line adsorption system for reducing cold-start ammonia emissions from engines fueled with ammonia and hydrogen

Ammonia-free emissions from an engine system fueled with ammonia and hydrogen during cold-start and warm-up periods are demonstrated. The fuels are supplied into a single-cylinder test engine under constant-speed conditions. The exhaust system consists of a redox catalyst followed by an in-line adsorber, the latter of which stores the ammonia that flows through the former. The results show that all adsorbers, H-ZSM-5, Cu-ZSM-5, and Pt-ZSM-5, can adsorb ammonia during cold-start conditions although the engine should be operated with retarded spark timing and a high hydrogen ratio because of low combustion efficiency at low coolant temperatures. Cu-ZSM-5 and Pt-ZSM-5 are regenerated after adsorption through their catalytic reactions without ammonia slip. Cu-ZSM-5, which has the largest adsorption capacity among the tested adsorbers, favors lean burn operation for regeneration. Pt-ZSM-5 has the advantage of simple regeneration control.

Experimental Investigation for NOx Emission Reduction in Hydrogen Fueled Spark Ignition Engine Using Spark Timing Retardation, Exhaust Gas Recirculation and Water Injection Techniques

The experimental tests were carried out on a single cylinder hydrogen fueled spark ignition (SI) generator set with different spark timings (4-20°CA bTDC), exhaust gas recirculation (EGR) up to 28% by volume and water injection up to 1.95 kg/h (maximum water to fuel mass ratio of 8:1). The engine speed was kept constant of 3000 r/min. The NOx emission and thermal efficiency of engine with gasoline and hydrogen fuel operation at 1.4 kW power output are 5 g/kWh and 12.1 g/kWh, and 15% and 20.9% respectively. In order to reduce the NOx emission at source level, retarding spark timing, exhaust gas recirculation (EGR), and water injection techniques were studied. NOx emission decreased with spark timing retardation, EGR, and water injection. NOx emission with hydrogen at 1.4 kW power output decreased from 12.1 g/kWh with maximum brake torque (MBT) spark timing (10°CA bTDC) to 8.1 g/kWh with retarded spark timing (4°CA bTDC) due to decrease in the in-cylinder peak pressure and temperature. The NOx emission decreased to 6.1 g/kWh with 20% EGR due to thermal and chemical dilution effect. However, thermal efficiency decreased about 33% and 17% with spark timing retardation and 20% EGR respectively as compared to that of MBT spark timing. But, in the case of water injection, the NOx emission decreased significantly without affecting the thermal efficiency of the engine and it is 5.6 g/kWh with water-hydrogen ratio of 4:1 (water flow rate of 0.92 kg/h). Water injection is the best suitable method to reduce the NOx emission in a hydrogen fueled engine compared with the spark timing retardation and EGR technique.

Back pressure effect on three-way catalyst light-off

The effect of back pressure on the light-off of a modern spark ignition engine three-way catalyst has been assessed by measuring the hydrocarbon conversion efficiency in a hot flow bench and in the cold-idle period in an engine. In the flow bench experiment, a small amount of propane/air mixture is used as a surrogate for the hydrocarbon mixture. The conversion efficiency is found to be only a function of temperature. The efficiency is independent of pressure, space velocity, and the equivalence ratio of the hydrocarbon mixture for λ ≥ 1. In the engine test, while the engine-out exhaust gas temperature is higher at a higher back pressure, there is little difference between the gas temperatures at the catalyst entrance for different back pressures at retarded spark timing. This observation is attributed to the larger amount of exhaust hydrocarbon conversion oxidation between the engine exit and the catalyst entrance with the lower back pressure. The heat release from this oxidation compensates for the lower engine-out exhaust temperature at the lower back pressure. The catalyst temperature increases modestly and light-off time shortens correspondingly at the higher back pressure. This observation is attributed solely to the increase in mass flow rate (and thus exhaust sensible enthalpy flow rate) of the engine needed to overcome the additional pumping loss due to the throttling of the exhaust. These results have been confirmed with a simple one-dimensional catalyst model.

Experimental investigation on effects of knocking on backfire and its control in a hydrogen fueled spark ignition engine

The experimental study was carried out on a multi-cylinder spark ignition engine fueled with hydrogen for analyzing the effect of knocking on backfire and its control by varying operating parameters. The experimental tests were conducted with constant speed at varied equivalence ratio. The equivalence ratio of 0.82 was identified as backfire occurring equivalence ratio (BOER). The backfire was identified by high pitched sound and rise in in-cylinder pressure during suction stroke. In order to analyze backfire at equivalence ratio of 0.82, the combustion analysis was carried out on cyclic basis. Based on the severity of in-cylinder pressure during suction stroke, the backfire can be divided into two categories namely low intensity backfire (LIB) and high intensity backfire (HIB). From this study, it is observed that there is frequent LIB in hydrogen fueled spark ignition engine during suction stroke, which promotes instable combustion and thus knocking at the end of compression stroke. This knocking creates high temperature sources in the combustion chamber and thus causes HIB to occur in the subsequent cycle. A notable salient point emerged from this study is that combustion with knocking can be linked with backfire as probability of backfire occurrence decreases with reduction in chances of knocking. Retarding spark timing and delaying injection timing of hydrogen were found to reduce the chances of backfire occurrence. The backfire limiting spark timing (BLST) and backfire limiting injection timing (BLIT) were found as 12 0bTDC and 40 0aTDC respectively.

Effect of spark timing on performance of a hydrogen-gasoline rotary engine

This paper aimed to study the effect of spark timing on performance of a hydrogen-gasoline dual-fuel rotary engine. For this aim, a modified rotary engine equipped with a dual-fuel port injection system was developed. An electronic management module (ECM) was specially made to command the fuel injection, excess air ratio and hydrogen volumetric fraction. In this study, the engine was operated at 4500rpm with a manifold absolute pressure (MAP) of 35kPa. Hydrogen volumetric percentage of total intake was kept at 0%, 3% and 6%, severally. When the hydrogen volumetric percentage was changed, the gasoline fraction was also adjusted to keep the mixture at the stoichiometric. For a specified hydrogen volumetric fraction, the ignition timing was varied from 24 to 42°CA BTDC (before top dead center) with a fixed interval of 2°CA. Experimental results showed that for a specific hydrogen volumetric percentage, the peak combustion pressure and chamber temperature were increased, brake thermal efficiency was first increased and then decreased with the increase of spark advance. Advancing spark timing caused the increased flame development period, the decreased flame propagation period and exhaust temperature. Cyclic variation was initially weaken and then deteriorated after raising spark advance. HC and NOx emissions were reduced after retarding spark timing. Spark timing had little effect on CO emission.

The interactions between IC engine thermodynamics and knock

The development of high efficiency spark-ignition internal combustion engines is often constrained by the occurrence of knock. Knock may result in engine damage, lower performance, and lower efficiency. The options for preventing knock often involve lower compression ratios, lower boost, retarded spark timing, and other design choices that are detrimental to engine performance and efficiency. Since knock is largely a function of the thermodynamic state of the unburned zone, the occurrence of knock is expected to be a strong function of the engine thermodynamics. The purpose of the current work is to couple a simple knock model with a comprehensive engine cycle simulation to determine the interactions between the engine thermodynamics and knock. This work has explored the effects of engine parameters such as compression ratio (4–12), engine speed (500–2500rpm), inlet pressure (50–100kPa), exhaust gas recirculation (0–25%), combustion duration and heat transfer on knock. In each case, the occurrence of knock is connected to the cylinder pressures and the gas temperatures of the unburned zone. For example for a compression ratio of 12, to avoid knock the brake thermal efficiency decreased from 36.5% to 34% due to retarding the combustion.