Emission Control with Lean Operation Using Hydrogen-Supplemented Fuel

<div class="section abstract"><div class="htmlview paragraph">Well-mixed lean or dilute SI engine operation can provide efficiency improvements relative to that of traditional well-mixed stoichiometric SI operation. However, the realized gains depend on the ability to ensure stable, complete and fast combustion. In this work, the influence of fuel type is examined for gasoline, E30 and E85. Several enabling techniques are compared. For enhanced ignition stability, a multi-pulse (MP) transient plasma ignition system is compared to a conventional high-energy inductive spark ignition system. Combined effects of fuel type and intake-gas preheating are examined. Also, the effects of dilution type (air or N<sub>2</sub>-simulated EGR) on lean efficiency gains and stability limits are clarified. The largest efficiency improvement is found for lean gasoline operation using intake preheating, showing the equivalent of a 20% fuel-economy gain relative to traditional non-dilute stoichiometric operation. The reason for gasoline’s larger efficiency improvement is its lower octane number which facilitates the use of end-gas autoignition to produce mixed-mode combustion. For these conditions, such mixed-mode combustion is required for rapid completion of the inherently slow lean combustion event prior to piston expansion. The fuel-economy gains are somewhat smaller for both E30 and E85 because of higher resistance to end-gas autoignition under lean conditions.</div><div class="htmlview paragraph">To avoid knocking cycles when mixed-mode combustion is used, the deflagration-based combustion must be very repeatable to ensure consistent compression of the end-gas reactants. Multi-pulse transient plasma ignition is used beneficially to stabilize the combustion, especially for dilute operation which suffers from low flame speeds. However, even with an enhanced ignition system, the best fuel-economy gains of dilute stoichiometric operation with mixed-mode combustion are on the order of 11-12%, which is substantially less than for lean operation.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The introduction of alternative fuels is crucial to limit greenhouse gases. CNG is regarded as one of the most promising clean fuels given its worldwide availability, its low price and its intrinsic properties (high knocking resistance, low carbon content...). One way to optimize dedicated natural gas engines is to improve the CNG slow burning velocity compared to gasoline fuel and allow lean burn combustion mode. Besides optimization of the combustion chamber design, hydrogen addition to CNG is a promising solution to boost the combustion thanks to its fast burning rate, its wide flammability limits and its low quenching gap.</div><div class="htmlview paragraph">This paper presents an investigation of different methane/hydrogen blends between 0% and 40 vol. % hydrogen ratio for three different combustion modes: stoichiometric, lean-burn and stoichiometric with EGR. The main objectives are to identify the complex mechanisms involved in the combustion process and to define the optimal hydrogen ratio for each combustion mode.</div><div class="htmlview paragraph">The study combines engine tests and 0D modeling. Tests were carried out on a spark-ignited single-cylinder engine adapted to CNG operation with 2 different compression ratios 9,5:1 and 11,5:1. Computations allow studying separately the different phenomena linked to the progressive addition of hydrogen in the fuel. Hence, using 0D modeling, the effects due only to the combustion speed evolution, as a function of hydrogen ratio in the fuel, were then quantified using experimental results as comparison basis.</div><div class="htmlview paragraph">The engine test results reveal that the impact of hydrogen is limited in stoichiometric conditions except for CO₂ savings. A ratio of 10 to 20 vol. % of hydrogen seems to be optimal to reach interesting HC emissions reduction without an excessive lowering of the operation range. The results are more encouraging for lean-burn operation as the lean limit of equivalence ratio is extended for more than 0,125 with 40 vol. % of hydrogen. NOx emissions and consumption were significantly reduced (-92% for NOx) while maintaining constant HC and CO emissions compared to methane operation. Hydrogen stabilizes and speeds up combustion especially in very diluted mixtures. Furthermore, hydrogen increases EGR tolerance for the same reasons as in lean-burn mode: in comparison, identical very-low NOx levels were reached with smaller consumption gains. Finally, the engine test results show that the highest tested ratio of hydrogen (up to 40%) in methane for very diluted mixtures with air or EGR drastically reduce NOx emissions without penalty on engine performances.</div><div class="htmlview paragraph">Computations prove that the evolution in terms of thermodynamic properties of the fuel is not the most important contribution to the evolution of combustion. The effect of hydrogen addition contributes mainly to increase the combustion speed. Moreover, lean burn operation results demonstrate that the increase of combustion speed due to hydrogen addition is enhanced. This can only be explained by the increase of thermo-diffusivity which has an opposite and larger effect than the slowdown of laminar flame velocity conventionally described in the literature.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The development and improvement of efficient compressed natural gas (CNG) engines align with efforts to reduce greenhouse gas and pollutant emissions. The objective of this study is to evaluate the flame structure and compare the performance characteristics of an engine powered by compressed natural gas (CNG) under stoichiometric and lean combustion in wide open throttle. CFD simulation alongside experimental tests are performed. The experimental data were obtained using a Hyundai 2.5-liter HR engine, originally a Diesel engine, adapted for spark ignition operation. Lean and stoichiometric conditions were evaluated at compression ratio 14:1, operating at 1800 rpm in MBT spark timing. The results showed that increasing lambda (<i>λ</i>) had a significant effect on apparent heat release rate, laminar flame speed, flame thickness and flame surface area. While the flame speed decreased in a leaner operating condition, the flame thickness and surface area increased due to reduced reaction rates and extended combustion duration. By reducing the flame speed but increasing its surface area, the amount of unburned fuel does not experience a significant increase, while the heat losses to the cylinder walls are reduced. When comparing the total energy between the two conditions and the indicated thermal efficiency, the lean operation achieved an absolute increase of almost 1% in efficiency, from 37.41% in stoichiometric condition to 38.34% in lean condition. This highlights the need to explore lean operation to increase the efficiency of internal combustion engines using natural gas.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Emission compliance at the production level has been a challenge for vehicle manufacturers. Diesel oxidation catalyst (DOC) plays a very important role in controlling the emissions for the diesel vehicles. Vehicle manufacturers tend to ‘over design’ the diesel oxidation catalyst to ‘absorb’ the production variations which seems an easier and faster solution. However this approach increases the DOC cost phenomenally which impacts the overall vehicle cost.</div><div class="htmlview paragraph">The main objective of this paper is to address the high variation in CO tail pipe emissions which were observed on a diesel passenger car during development. This variation was posing a challenge in consistently meeting the internal product requirement/specification. This paper outlines a step by step process by following a DFSS (Design for Six Sigma) methodology in selecting an optimized DOC design in terms of tailpipe emission, engine performance and system cost for a given level of engine-out CO emission variation in a cheaper and faster way by combining concepts of virtual emission simulation, Taguchi design of experiments and multi parameter optimization.</div><div class="htmlview paragraph">In order to quantify the emission variation, engine-out & tail pipe emissions were measured on various development vehicles with the same level of hardware and calibration. Further, a parameter diagram (P-diagram) which identified all the control factors, input signal, and noise and error states was developed. The optimal values of control parameters were arrived by rationalizing the DOC design against DOC system cost and other performance criteria using multi parameter optimization methods.</div><div class="htmlview paragraph">The optimized DOC design had a 14% reduction in CO emissions and a ∼14% improvement in robustness based on signal to noise ratio when compared with the baseline design that was being used during development. Monte Carlo simulations predicted an 87% reduction in out-of-specification emissions for an additional 23% increase in cost when compared to baseline.</div></div>

<div class="section abstract"><div class="htmlview paragraph">For gasoline engine, thermal efficiency can be improved by using lean burn. However, combustion instability occurs when gasoline engine is operated on lean condition. Hydrogen has features that can be used for improving combustion stability of gasoline engine. In this paper, an experimental study of hydrogen effect on lean limit was carried out using a four-cylinder 2.0L turbo gasoline direct injection engine. The engine torque was fixed at 110Nm on 1600RPM, 2000RPM and 2400RPM. The results showed that lean limit was extended and brake thermal efficiency was improved by hydrogen addition. Especially, at lower engine speed, the large improvement of lean limit was achieved. However, improvement of brake thermal efficiency was achieved at high speed. HC and CO<sub>2</sub> emissions were decreased and NO emissions increased with hydrogen addition. CO emissions were slightly reduced with hydrogen addition.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The pressing need to improve U.S. energy independence and reduce climate forcing fossil fuel emissions continues to motivate the development of high-efficiency internal combustion engines. A recent trend has been to downsize and turbocharge automotive spark-ignited engines coupled with direct fuel injection to improve engine efficiency while maintaining vehicle performance. In-line with recent trends in state-of-the-art engine technology, the focus of this study is lean and EGR dilute combustion in a gasoline direct injection (GDI) engine.</div><div class="htmlview paragraph">The lean and dilute operating limits are defined by combustion stability typically in terms of COV<sub>IMEP</sub> so experiments were carried out on an automotive size single-cylinder research engine to characterize combustion stability. From a 20,000 cycle sequence analysis, lean operating conditions exhibit binary high- to low-IMEP cycle sequences. This may be because the cycle-to-cycle feedback mechanisms are physically limited to one or two cycles. Longer sequences are observed with EGR likely because the EGR loop introduces a much longer transient feedback mechanism.</div><div class="htmlview paragraph">Results from a sensitivity study with induced variability show that COV<sub>IMEP</sub> is far less sensitive to ignition perturbation than to injection perturbation while the sensitivity is similar in terms of efficiency. This is true for both lean and EGR dilute operation; however, one difference that stands out with EGR is the sensitivity of COV<sub>IMEP</sub> to ignition perturbation. Increased sensitivity to ignition perturbation is likely the result of longer ignition delay which is critical for early flame kernel development.</div></div>

<div class="htmlview paragraph">Single-cylinder engine tests, an analytical engine cycle simulation, and automobile tests were employed to study the effects of supplementing gasoline with water for use in spark ignition engines. Factors examined include: the method of water addition (both water-in-gasoline emulsions and direct manifold water addition), antiknock characteristics with water addition, MBT spark requirement, indicated engine efficiency, engine cooling requirement, exhaust emissions, volumetric efficiency, lean operating limit, smoke level, exhaust temperature, and vehicle driveability. Among the negative aspects of water addition were increased hydrocarbon emissions and decreased vehicle driveability. Also, the polyoxyethylene type of emulsifier used in the water-in-gasoline emulsions, gave poor fuel stability and caused a rapid buildup of engine deposits. However on the positive side, water-gasoline fuels have higher octane ratings and decrease nitric oxide emissions.</div>

<div class="section abstract"><div class="htmlview paragraph">Combustion simulations and single cylinder engine tests show a clear potential when coupling the Variable Compression Ratio (VCR) engine with the Variable Valve Actuation (VVA) technologies.</div><div class="htmlview paragraph">Simulations demonstrate the thermodynamic benefit from increasing the geometric Compression Ratio (CR>18:1) in combination with VVA compared to VVT strategies, thanks to the use of Atkinson / Miller Cycles. 3D combustion simulations of high compression ratio combustion chamber geometries used with Early or Late Intake Valve Closing strategies have been carried out with IFP-C3D™. They show an indicated efficiency increase up to 12 or 13% between compression ratio 10:1 and 18-20:1 at low loads (BMEP < 8 bar).</div><div class="htmlview paragraph">Single cylinder engine tests have been performed with specific combustion chambers up to CR 23:1 and have confirmed the simulation results.</div><div class="htmlview paragraph">0D GT-POWER™ simulations have been correlated to the engine tests and used to extrapolate them to a 3 cylinders 1.1L TGDI VCR-VVA engine, for both EIVC and LIVC intake valve lift strategies.</div><div class="htmlview paragraph">Finally, simulations and tests show correlated thermodynamic benefits of the association of VCR and VVA, improving fuel consumption on driving cycles between 8 and 11% compared to a 10.5:1 fixed compression ratio engine equipped with 2 VVT. Combining the VCR and VVA optimizes each potential far more than when separated (alone). Furthermore, the fuel consumption benefit is robust through driving cycles and downsizing level. </div></div>

<div class="section abstract"><div class="htmlview paragraph">The increased availability of natural gas (NG) in the United States (US) and its relatively low cost compared to diesel fuel has heightened interest in the conversion of medium duty (MD) and heavy duty (HD) engines to NG fueled combustion systems. The aim for development for these NG engines is to realize fuel cost savings and reduce harmful emissions while maintaining durability. Transforming part of the vehicle fleet to NG is a path to reduce dependence on crude oil.</div><div class="htmlview paragraph">Traditionally, port-fuel injection (PFI) or premixed NG spark-ignited (SI) combustion systems have been used for MD and HD engines with widespread use in the US and Europe. But this technology exhibits poor cycle efficiency and is load limited due to knock phenomenon. Direct Injection of NG during the compression stroke promises to deliver improved thermal efficiency by avoiding excessive premixing and extending the lean limits which helps to extend the knock limit.</div><div class="htmlview paragraph">In this work, a single cylinder engine with 14:1 compression ratio (CR) was used to investigate spark ignited direct injection (SIDI) NG combustion using an integrated spark injector-igniter. Two parameters controlling dilution were investigated (i) increased air charge resulting in an increased air-fuel ratio (AFR) and (ii) exhaust gas recirculation (EGR). The impact of these parameters on fuel consumption, combustion stability, phasing, knock, and emissions of NOx, HC, CO is investigated and reported in this work. Partially stratified combustion (PSC) SOI and SPK timings from previous work will be used as a starting point to investigate the effects. Overall, both AFR and EGR were effective in controlling knock and NOx emissions; however, EGR required lower levels to obtain the desired effect. The use of charge dilution in the PSC range showed promise of trading off knock and combustion stability to within acceptable limits, thus demonstrating potential for increased load operation.</div></div>

<div class="htmlview paragraph">Regulated and non-regulated emissions from five current European diesel passenger cars and one light-duty diesel truck were measured to assess the environmental impact of diesel vehicles and to help determine the emission characteristics of the two types of combustion systems: indirect injection (IDI) and high speed direct injection (HSDI). The vehicle emissions were measured using the European Motor Vehicle Emissions Group (MVEG) cycle and the U.S. Federal (FTP 75) test procedures. Measured emissions included HC, CO, NO<sub>x</sub> and particulate mass (PM), C<sub>1</sub> to C<sub>12</sub> hydrocarbon species (here called light hydrocarbon or LHC), aldehydes, particulate composition and particle size distribution. The particulate composition measurements included soluble organic fraction (SOF), its oil and fuel sub-fractions, and the sulfate fraction. All passenger cars and the light-duty commercial vehicle tested complied with the current European Emissions Directive 91/441/EEC. Two passenger cars achieved the EEC Stage 2 levels, and one nearly met the 1994 Tier I U.S. Federal standards. The LHC accounted for between 35 to 78% of the total HC measured by the heated FID analyzer. Fuel and oil comprised between 12 and 30% of the PM emissions. The non-methane organic gases (NMOG) emissions and the LHC ozone reactivity from diesel cars were both about 50% less than those from gasoline cars. Of the non-regulated emissions, formaldehyde was generally below 0.009 g/km, and benzene emissions were below 0.0035 mg/km. The results were compared with European gasoline vehicles and the Current Gasoline Vehicle fleet of the U.S. Air Quality Improvement Program (AQIRP), and an assessment was made of the relative environmental impacts of gasoline and diesel vehicles.</div> <div class="htmlview paragraph">Over the last 20 years, there has been a substantial effort to lower the exhaust emissions from both diesel and gasoline passenger vehicles. Over the same period, the percentage of diesel passenger vehicles purchased in Europe has been increasing steadily(<span class="xref">1</span>)<span class="xref">*</span>. Lower operating(<span class="xref">2</span>) and maintenance costs, and better durability with equivalent drive performance appear mainly responsible for the increased diesel sales. However, even though both diesel and gasoline vehicles meet the current emission standards, questions have arisen about their relative impact on the environment(<span class="xref">3</span>). In addition, with future requirements for lower emissions, these questions will undoubtedly continue.</div> <div class="htmlview paragraph">The relative environmental impact of diesel and gasoline vehicles is still uncertain because there are relatively few published data on the emissions of current diesel vehicles and because the environmental impacts of the expected emissions are not clearly understood. Data on the regulated emissions for diesel passenger vehicles sold in Europe are available from the German Government:(<span class="xref">4</span>) starting in 1991. There are also published reports on regulated emissions from late 1980 and early 1990 diesel cars in the literature(<span class="xref">5</span>,<span class="xref">6</span>,<span class="xref">7</span>). Still there are few reports on the non-regulated emissions from current diesel vehicles(<span class="xref">8</span>,<span class="xref">9</span>,<span class="xref">10</span>).</div> <div class="htmlview paragraph">On the other hand, there are substantial published data on the regulated emissions of current gasoline vehicles(<span class="xref">11</span>). In addition, there are substantial data on the non-regulated emissions of gasoline cars, especially from the U.S. Air Quality Improvement Research Program (AQIRP)(<span class="xref">12</span>). The AQIRP emissions data included measurements of over 150 individual hydrocarbon and aldehydic compounds which allow estimates of the amount of urban ozone formed from the exhaust and of the atmospheric toxic compound levels. Diesel vehicles were not included in AQIRP.</div> <div class="htmlview paragraph">This paper reports on detail regulated and non-regulated emissions measurements for six 1992/93 model year diesel vehicles, including two Ford and four competitor vehicles. The emissions were measured on both the 1993 European MVEG cycle and the U. S. Federal test procedure. The U. S. AQIRP analytical methods were used for hydrocarbon and aldehydic speciation. The report discusses the regulated emissions from the six diesel vehicles compared to emissions standards, their contribution to urban ozone formation, toxic levels and global warming. It also compares the exhaust emissions of current diesel and gasoline vehicles to help clarify their relative environmental impact.</div>

<div class="htmlview paragraph">Direct injection natural gas engines need to produce in the mixing process between the fuel jet and the air in the cylinder a “stratified” fuel-air mixture, with an easily ignitable composition near the spark plug at the time of ignition.</div> <div class="htmlview paragraph">Stratified-charge engines have a tendency to produce high NOx emissions due to the high temperature of burning areas at the start of combustion since the fuel-air mixture is not uniform. Therefore, it is necessary to reduce NOx emissions from direct injection natural gas engines.</div> <div class="htmlview paragraph">The objective of this study is to investigate measures to reduce emissions, especially NOx emissions, from direct injection natural gas engines. A single cylinder test engine was equipped with a newly developed high-pressure electromagnetic injector and a spark plug.</div> <div class="htmlview paragraph">The possibility of reducing emissions, especially NOx emissions, while maintaining high thermal efficiency was investigated by means of multiple stage injection with a test engine using an electromagnetic injector, and by means of control of oxygen concentrations in intake air by adding nitrogen (a method like EGR control).</div>

Increasing on gaseous fuels as clean, economical and abundant fuels encourages the search for optimum conditions of gas-fueled internal combustion engines. This paper presents the experimental results on the lean operational limits of Recardo E6 engine using gasoline, LPG, NG and hydrogen as fuels. The first appearance of almost motoring cycle was used to define the engine lean limit after the fuel flow was reduced gradually. The effects of compression ratio, engine speed and spark timing on the engine operational limits are presented and discussed in detailed. Increasing compression ratio (CR) extend the lean limits, this appears obviously with hydrogen, which has a wide range of equivalence ratios, while for hydrocarbon fuel octane number affect gasoline, so it can' t work above CR=9:1, and for LPG it reaches CR=12:1, NG reaches CR=15:1 at lean limit operation. Movement from low speeds to medium speeds extended lean misfire limits, while moving from medium to high speeds contracted the lean misfiring limits. NOx, CO and UBHC concentrations increased with CR increase for all fuels, while CO 2 concentrations reduced with this increment. NOx concentration increased for medium speeds and reduced for high speeds, but the resulted concentrations were inconcedrable for these lean limits. CO and CO 2 increased with engine speed increase, while UBHC reduced with this increment. The hydrogen engine runs with zero CO, CO 2 and UNHC concentrations, and altra low levels of NOx concentrations at studied lean misfire limits

<div class="section abstract"><div class="htmlview paragraph">To comply with the ambitious CO<sub>2</sub> targets of the European Union, greenhouse gas emissions from the transport sector should be eliminated by 2050. Incremental powertrain improvement and electrification are only a part of the solution and need to be supplemented by carbon-neutral fuels. Due to the high technology readiness level, biofuels offer a short-term decarbonization measure. The high process energy demand for transesterification or hydrotreating however, hinders the well-to-wheel CO<sub>2</sub> reduction potential of current market biodiesels. An often-raised, economically and energetically feasible alternative is to use unprocessed oils with viscosity and cold-properties improvers instead. The present work investigates the suitability of one such biofuel (Plantanol<sup>TM</sup>) for advanced common rail engines operating in a partially premixed compression ignition mode. Preliminary investigations are carried out on a Euro VIb light-duty car engine. The main focus is on the influence of the fuel blend on the soot/NO<sub>X</sub> emission trade-off without changing the engine control maps. Single-cylinder engine tests are then focused on the optimization potential of injection parameters and external EGR to reach optimum performance-emissions trade-off on the new fuel. The results highlight that at the factory map setting, without EGR, biofuel offers slightly reduced thermal efficiency with respect to diesel, as a joint effect of retarded combustion and elevated THC and CO emissions. NO<sub>X</sub> emissions are reduced by 20% at both non-EGR and to 25% EGR operation. With injection parameters optimization, the combustion phasing can be adjusted to diesel-like values while keeping the NO<sub>X</sub> reduction benefits. The tested bio-oil blend is however sensitive to EGR, where increasing the recirculation rate retards the combustion while the soot emissions increase almost five-fold over the non-EGR baseline.</div></div>

<div class="htmlview paragraph">The objective of this study was to develop an innovative microwave-induced plasma ignition system to improve the fuel economy of a current engine and achieve a higher efficiency without any configuration modifications. A new plasma generation technique was proposed for a stable and intense ignition source. A microwave plasma combustion system was developed consisting of a spark plug, microwave transfer system, and control system. A magnetron, like that found in a microwave oven, was used as a microwave oscillator. The spark plug had a microwave antenna inside that generated plasma in the engine cylinders. The microwave transfer system transmitted microwave power from the oscillator to the antenna. Combustion experiments were performed using a single-cylinder research engine. The microwave plasma expanded the range of lean operating conditions. The single-cylinder engine had an indicated mean effective pressure (IMEP) of 275 kPa at an engine speed of 2000 rpm. The threshold of the lean limit was defined as a coefficient of variation (COV) of 5% at the IMEP. For the plasma ignition case, the combustion was stable even in the lean condition, and the COV remained under 2% up to an air-to-fuel ratio (A/F) of 22%. The lean limit improved from 19.3 to 24.1 with the plasma ignition.</div>

<div class="section abstract"><div class="htmlview paragraph">Electrical power and efficiency are decisive factors to minimise payoff time of cogeneration units and thus increase their profitability. In the case of (small-scale) cogeneration engines, low-NO<sub>x</sub> operation and high engine efficiency are frequently achieved through lean burn operation. Whereas higher diluted mixture enables future emission standards to be met, it reduces engine power. It further leads to poor combustion phasing, reducing engine efficiency.</div><div class="htmlview paragraph">In this work, an engine concept that improves the trade-off between engine efficiency, NO<sub>x</sub> emissions and engine power, was investigated numerically. It combines individual measures such as lean burn operation, overexpanded cycle as well as a power- and efficiency-optimised intake system.</div><div class="htmlview paragraph">Miller and Atkinson valve timings were examined using a detailed 1D model (AVL BOOST). Indicated specific fuel consumption (ISFC) was improved while maintaining effective compression ratio constant. However, brake specific fuel consumption (BSFC) rises due to lower IMEP. In order to take advantage of the reduced ISFC, the intake section was optimised through virtual Design of Experiments (DoE). Subsequently, intake swirl was reduced, leading to further benefits in charging and engine efficiency. For both Miller and Atkinson cycle the efficiency was increased, while meeting the reference engine's baseline NO<sub>x</sub> emissions and IMEP.</div></div>