Light-duty Engine Research Articles

Investigation of Cold Starting and Combustion Mode Switching as Methods to Improve Low Load RCCI Operation

Reactivity controlled compression ignition (RCCI) is an engine combustion strategy that utilizes in-cylinder fuel blending to produce low NOx and particulate matter (PM) emissions while maintaining high thermal efficiency. The current study investigates RCCI and conventional diesel combustion (CDC) operation in a light-duty multicylinder engine (MCE) using a transient capable engine test cell. The main focus of the work uses engine experiments to investigate methods which can improve low load RCCI operation. The first set of experiments investigated RCCI operation during cold start conditions. The next set of tests investigated combustion mode switching between RCCI and CDC. During the cold start tests, RCCI performance and emissions were measured over a range of engine coolant temperatures (ECTs) from 48 °C to 85 °C. A combination of open- and closed-loop controls enabled RCCI to operate at a 1500 rpm, 1 bar BMEP operating point over this range of coolant temperatures. At a similar operating condition, i.e., 1500 rpm, 2 bar BMEP, the engine was instantaneously switched between CDC and RCCI combustion using the same open- and closed-loop controls as the cold start testing. During the mode switch tests, emissions and performance were measured with high-speed sampling equipment. The tests revealed that it was possible to operate RCCI down to 48 °C with simple open- and closed-loop controls with emissions and efficiency similar to the warm steady-state values. Next, the mode switching tests were successful in switching combustion modes with minimal deviations in emissions and performance in either mode at steady state.

Evaluation of a Semiempirical, Zero-Dimensional, Multizone Model to Predict Nitric Oxide Emissions in DI Diesel Engines’ Combustion Chamber

In the present study, a semiempirical, zero-dimensional multizone model, developed by the authors, is implemented on two automotive diesel engines, a heavy-duty truck engine and a light-duty passenger car engine with pilot fuel injection, for various operating conditions including variation of power/speed, EGR rate, fuel injection timing, fuel injection pressure, and boost pressure, to verify its capability for Nitric Oxide (NO) emission prediction. The model utilizes cylinder’s basic geometry and engine operating data and measured cylinder pressure to estimate the apparent combustion rate which is then discretized into burning zones according to the calculation step used. The requisite unburnt charge for the combustion in the zones is calculated using the zone equivalence ratio provided from a new empirical formula involving parameters derived from the processing of the measured cylinder pressure and typical engine operating parameters. For the calculation of NO formation, the extended Zeldovich mechanism is used. From this approach, the model is able to provide the evolution of NO formation inside each burned zone and, cumulatively, the cylinder’s NO formation history. As proven from the investigation conducted herein, the proposed model adequately predicts NO emissions and NO trends when the engine settings vary, with low computational cost. These encourage its use for engine control optimization regarding NOxabatement and real-time/model-based NOxcontrol applications.

Black Box SCR Modeling and Control for Small CI Engines

Selective catalytic reduction (SCR) has become widely used to reduce NOx emissions especially for medium and heavy duty CI engines, while lean NOx traps (LNT) are a typical choice for light duty engines. In the field of small engines, SCR is usually not applied, because an expensive additional AdBlue supply is necessary and the emission limits can be also achieved with less complex methods. Nevertheless, if the engine is used as range extender of a hybrid electric vehicle, in engine-only operation it must also fulfill the Diesel emission legislation. There SCR is a sensible and maybe in view of future legislation only choice. A key problem of this choice, is that for small engines, typically the available space for the SCR is limited and leads to a strongly reduced storage capability of the catalyst. Some of the features of a small system render a purely data based approach feasible as system dynamics are faster and phenomenon like storage are less pronounced. Thus in this work a black box modeling approach is presented and combined with an NMPC strategy for closed loop SCR control. The proposed control strategy is validated in simulation and experiments on a testbench.

Study on combustion and emission characteristics of Polyoxymethylene Dimethyl Ethers/diesel blends in light-duty and heavy-duty diesel engines

Diesel and Polyoxymethylene Dimethyl Ethers (PODE3–4)/diesel blends with 10–30% PODE3–4 by volume were tested in a light-duty (LD) direct injection diesel engine without any modifications on the engine fuel supply system. Engine performance, combustion and emission characteristics were compared at various loads. The results show that diesel engines are able to work normally fueled by blend fuel ratio with lower than 30% PODE3–4. Adding PODE3–4 improve engine efficiency and reduce soot and CO emissions significantly without a serious impact on NOx emissions. P20 is the optimal choice among these blends because it has much lower soot emissions than diesel and P10 and slightly lower NOx emissions than P30. The European Stationary Cycle (ESC) was also carried out in a six-cylinder heavy-duty (HD) production diesel engine fueled with pure diesel and P20, and the results were similar to those of the LD engine. It is proved that PODE3–4, of which the mass production has been achieved recently, is a promising additive component for diesel fuel.

Experimental Investigation on CNG-Diesel Combustion Modes under Highly Diluted Conditions on a Light Duty Diesel Engine with Focus on Injection Strategy

In the last decades, emission legislation on pollutant emissions generated by road transportation sector has become the main driving force for internal combustion engine development. Approximately 20% of worldwide emissions of carbon dioxide from fuel combustion come from the transportation sector, and road vehicles contribute up to 80% of those emissions [1]. Light-duty methane gas engines are usually spark-ignited due to similar combustion characteristics for methane gas and gasoline. Since spark ignition requires a low compression ratio to avoid knock problems, gas engines have lower efficiency than diesel engines. Acombustion concept that has been successfully applied on large stationary engines and to some extent on heavy-duty engines is dual-fuel combustion, where a compression-ignited diesel pilot injection is used to ignite a homogeneous charge of methane gas and air. This dual-fuel combustion concept is well established for large stationary engines and exists as an after-market solution for heavy-duty engines but does not exist at all for light-duty engines. This concept offers a high degree of flexibility for the engine operation because dual fuel combustion does not require heavy modifications of the original diesel engine architecture so diesel operation could remain unaltered.This paper presents an initial study of how combustion characteristics in a multi-cylinder dual fuel methane-diesel light duty engine are altered by the injection control strategy adopted on different high substitution ratio operating points under highly diluted conditions (unthrottled). The measurements have been performed under steady state conditions but the impact of injection strategy on transient operation is discussed and analyzed based on emissions and brake thermal efficiency. Results show that high substitution ratios are difficult to operate at low loads regardless the operation mode selected. RCCI or PPCI combustion could be adopted to promote more stable and robust combustion, although those modes require lower substitution ratios to be achieved. This investigation does not aim for an optimization of the injection parameters in dual fuel combustion mode, but it aims to point out and understand the most relevant characteristics and behaviors of a light duty dual fuel CNG-Diesel engine operating under high substitution ratios.

Effects of Exhaust Gas Recirculation and Boost Pressure on Reactivity Controlled Compression Ignition Engine at High Load Operating Conditions

Reactivity controlled compression ignition (RCCI) at engine high load operating conditions is investigated in this study. The effects of exhaust gas recirculation (EGR) and boost pressure on RCCI combustion were studied by using a multidimensional computational fluid dynamics (CFD) code. The model was first compared with a previous CFD model, which has been validated against steady-state experimental data of gasoline–diesel RCCI in a multicylinder light duty engine. An RCCI piston with a compression ratio of 15:1 was then proposed to improve the combustion and emissions at high load. The simulation results showed that 18 bar indicated mean effective pressure (IMEP) could be achieved with gasoline–diesel RCCI at an EGR rate of 35% and equivalence ratio of 0.96, while the peak pressure rise rate (PPRR) and engine combustion efficiency could both be controlled at reasonable levels. Simulations using both early and late direct-injection (DI) of diesel fuel showed that RCCI combustion at high load is very sensitive to variations of the EGR amount. Higher IMEP is obtained by using early diesel injection, and it is less sensitive to EGR variation compared to late diesel injection. Reduced unburned hydrocarbon (HC), carbon monoxide (CO), soot and slightly more nitrogen oxides (NOx) emissions were seen for early diesel injection. HC, CO, and soot emissions were found to be more sensitive to EGR variation at late diesel injection timings. However, there was little difference in terms of peak pressure (PP), efficiencies, PPRR, and phasing under varying EGR rates. The effect of boost pressure on RCCI at high load operating conditions was also studied at different EGR rates. It was found that combustion and emissions were improved, and the sensitivity of the combustion and emission to EGR was reduced with higher boost pressures. In addition, cases with similar combustion phasing and reasonable PPRR were analyzed by using an experimentally validated GT-Power model. The results indicated that although higher IMEP was generated at higher boost pressures, the brake mean effective pressure (BMEP) was similar compared to that obtained with lower boost pressures due to higher pumping losses.

Structural evolution of soot particles during diesel combustion in a single-cylinder light-duty engine

The structural evolution of soot particles in a single-cylinder, light-duty diesel engine has been investigated by conducting thermophoretic soot sampling and subsequent transmission electron microscope (TEM) imaging. The location of TEM grid with respect to a diesel flame is varied so that soot particles are sampled at three different combustion stages including (1) when the impingement of flame on the wall occurs, (2) after the flame impingement, and (3) during the late-cycle burn-out. For comparison purposes, engine-out soot particles are also collected at the same operating conditions. The results show that diesel soot particles are aggregates of varying numbers of primary particles. It is found that the flame impingement on the wall makes a significant impact on the soot aggregate structures, evidenced by the decreased mean radius of gyration of the aggregates from 38 to 26nm between the wall-impinging and post-impingement stages. This was due primarily to the fragmentation of large soot aggregates while the mean diameter of primary particles remains the same. From the post-impingement to late-cycle burn-out stages, most of the soot aggregates disappear due to the oxidation leaving only highly agglomerated substructures. As a result, soot aggregates show higher fractal dimension in the late-cycle burn-out stage than that in the previous stages. The intensive soot oxidation also reduces primary particle diameter from 19 to 15nm through surface oxidation. The engine-out soot samples show similar particle size and structure to the late-cycle samples, suggesting that the late-cycle soot particles experienced little oxidation before exiting through the exhaust. This leads to a conclusion that the highly agglomerated substructures of soot aggregates can survive the late-cycle burn-out and become a major contributor to exhaust soot emissions.

Visualizations of combustion and emissions characteristics in a light-duty diesel engine with achieved premixed low temperature combustion

This paper presents a study on the feasibility of premixed low temperature combustion (PLTC) in a light-duty engine, employing moderate early injection (MEI) and high level exhaust-gas recirculation (EGR). Tests were carried out under constant speed and low load. In-cylinder pressure was measured for heat release rate analysis and exhaust emissions were measured in the exhaust pipe. To capture spray and combustion images, an optical diesel engine equipped with an endoscope and a color CCD camera was used. In addition, the AVL-Thermo Vision software was applied into the measurement of temperature and soot distribution of diffusion flame. The influence of injection timing and oxygen concentration on combustion and emissions characteristics were studied. With moderate advanced injection, premixed combustion was observed from the heat release rate and combustion images. Diffusion flame and soot emissions reduced evidently while NOx emissions increased and combustion phase occurred earlier. The introduction of EGR delayed combustion phasing to approach TDC, thus enhancing combustion thermal efficiency. The NOx decreased monotonically with increasing level of EGR and Soot emissions decreased under the condition of very low oxygen concentration. MEI coupled with high level EGR have high potential to decrease Soot and NOx simultaneously.

Response Characteristics of PMP Compliant Condensation Particle Counters Toward Various Calibration Aerosols

Within the European legislation, a new limit for particle emissions of light and heavy duty engines based on the particle number (PN) was established in 2011. For PN determination, solid exhaust particles are quantified by means of a condensation particle counter (CPC). In literature, deviations in PN of up to 30% are reported for a comparison of different measurement set-ups. Among others variations in the counting efficiency (CE) of different CPCs have to be considered as possible error sources that contribute to the overall deviation in PN. Thereby the uncertainties in CE may result from variations in the calibration procedure of different manufacturers (e.g., calibration aerosol). To investigate this circumstance, devices from three different manufacturers were directly compared according to their CE for model aerosols. The subject CPCs exhibited differences of up to 17% (23 nm particles) in the counting efficiency when measuring simultaneously the same test aerosol. Depending on the PN size distribution in real exhaust, this might result in an error (∼9%) in the finally determined PN. Additionally, the CPC response for selected volatile exhaust components was investigated. In this way, we found out that the fraction of detected nucleation mode particles increases approximately by factor 3 in case particles consist of or contain volatile material (e.g., sulfuric acid).Copyright 2015 American Association for Aerosol Research

Potential for using a tire pyrolysis liquid-diesel fuel blend in a light duty engine under transient operation

A tire pyrolysis liquid (TPL) has been blended in 5vol.% with commercial diesel fuel (5TPL) and tested in a light-duty diesel Euro 4 engine (with all technologies for meeting Euro 5) under transient operation by means of Road Load Simulation (RLS) and simulating the New European Driving Cycle (NEDC). Commercial diesel fuel has also been tested for comparative purposes. In order to characterize engine operation, parameters such as relative fuel/air ratio, exhaust gas recirculation (EGR) valve opening and coolant temperature have been registered. Regulated (THC, NOx, CO) and unregulated gaseous emissions (CH4, C2H4, C3H6 and SO2), smoke opacity and particulate matter (PM) emissions have been monitored for both fuels (5TPL and diesel fuels) during the tests. The EGR valve opening has resulted to be slightly higher for 5TPL than that for diesel fuel. Although the EGR valve opening has some influence on the gaseous emissions, both properties and composition of the 5TPL also showed an important effect. In this regard, these results have demonstrated the potential usage of the TPL for being blended with commercial diesel fuel for light-duty diesel engines without constructive modifications although some properties of TPL should be improved if the blending percent is intended to be increased. Thus, the reduction of sulfur content seems to be one of the major issues to be overcome if both lower THC and PM emissions, and marginal sulfur poisoning of the catalyst are wished.

System comparison for PMP Particle number determination

The relevance of a reliable and accurate determination of the particle number in engine exhaust steadily increases due to the expansion of particle number limits from light-duty diesel- over heavy-duty diesel- through to light-duty gasoline-diesel engines, but also as a reference for a future mobile determination of the particle number. At the Institute for Internal Combustion Engines of the Technische Universitat Munchen, a comparison of four parallel-operated partial flow dilution- and particle counting systems for particle number determination on a heavy-duty engine was conducted as part of a FVV project.

Experimental Investigation of Piston Heat Transfer in a Light Duty Engine Under Conventional Diesel, Homogeneous Charge Compression Ignition, and Reactivity Controlled Compression Ignition Combustion Regimes

Abstract : An experimental study has been conducted to provide insight into heat transfer to the piston of a light-duty single-cylinder research engine under Conventional Diesel (CDC), Homogeneous Charge Compression Ignition (HCCI), and Reactivity Controlled Compression Ignition (RCCI) combustion regimes. Two fast-response surface thermocouples embedded in the piston top measured transient temperature. A commercial wireless telemetry system was used to transmit thermocouple signals from the moving piston. A detailed comparison was made between the different combustion regimes at a range of engine speed and load conditions. The closed-cycle integrated and peak heat transfer rates were found to be lower for HCCI and RCCI when compared to CDC. Under HCCI operation, the peak heat transfer rate showed sensitivity to the 50% burn location.

Ethanol effect as premixed fuel in dual-fuel CI engines: Experimental and numerical investigations

Dual fuel configurations in compression ignition engines are considered as a promising solution to rely on alternative fuels that allows to respect at the same time the strict regulations on pollutants emissions. Looking at ethanol as one of the future transport biofuels, the authors investigate on the use of ethanol as the premixed fraction in a dual fuel engine. The activity is specifically focused on a light duty engine, since the dual fuel concept application, already implemented in heavy duty vehicles, was recently taken into account for smaller engines in automotive applications too.In the present paper the results of two research activities are reported and compared: tests on an optical single cylinder research engine and numerical simulations, so achieving a combined approach to the study of dual-fuel configuration.Optical diagnostics has been applied in a transparent direct injection diesel engine equipped with the head of an Euro5 commercial engine and the latest generation common rail injection system. Pure ethanol is injected in the intake manifold, while n-heptane is directly injected in the cylinder. UV digital imaging is applied to the optical engine allowing to detect crucial chemical intermediates, like OH, HCO, and CO, in terms of their spatial distribution and temporal evolution. This analysis allows to identify in-cylinder zones with high reactivity of mixed fuels and to investigate the effect of the presence of ethanol on the burning dynamics of the directly injected fuel.Numerical simulations are carried out by means of the OpenFOAM® library, that represents the closed valve phase of the engine cycle. Thanks to the adoption of detailed reaction kinetics, the predicted spatial distributions of the selected reaction intermediates are compared with the images provided by optical diagnostics. Moreover, the integrated emission intensity from the chosen chemical species is compared to the corresponding total concentration calculated histories, in order to verify the coherence of the numerical results also in terms of temporal evolution.

Comparison of Low Temperature Combustion Strategies for Advanced Compression Ignition Engines with a Focus on Controllability

In the present study, various low temperature combustion strategies were investigated using single cylinder engine experiments. The combustion strategies that were investigated premix the majority of the fuel and do not require exhaust gas recirculation (EGR) to achieve ultra-low NOx and soot emissions for low- to mid-load engine operation. These types of advanced compression ignition combustion strategies have been shown to have challenges with combustion phasing control. The focus of the study was to compare engine performance and emissions, combustion sensitivity to intake conditions, and the ability to control any observed sensitivity through the fuel injection strategy. Even though these are steady state engine experiments, this will demonstrate a given combustion strategies controllability on a cycle-to-cycle basis. The combustion strategies that were investigated are fully premixed dual-fuel homogeneous charge compression ignition (HCCI), dual-fuel reactivity controlled compression ignition (RCCI), and single-fuel partially premixed combustion (PPC). The baseline operating condition was an engine load representative of a light-duty engine: 5.5 bar gross indicated mean effective pressure (IMEP) and 1500 rev/min. At the baseline operating condition, in which the boundary conditions were chosen to yield near optimal engine performance, all three combustion strategies demonstrated high gross indicated efficiency (∼47%) and ultra-low NOx and soot emissions. By perturbing the intake conditions, it was found that all three combustion strategies display similar combustion phasing sensitivities. Both dual-fuel HCCI and RCCI were able to readily correct the observed sensitivities through the global fuel reactivity with no negative implications on the NOx emissions. However, single-fuel PPC was unable to correct for the observed combustion phasing sensitivity and, in some cases, had negative implications on the NOx emissions.

The Effects of Injection Parameters on the Performance of Common Rail Light Duty Engine Fueled with Palm Oil Biodiesel

It is in the interest of proponents of biodiesel to increase the utilization of the renewable fuel. The similarities of the methyl ester properties to diesel fuel and its miscibility proved to be an attractive advantage. It is however generally accepted that there are some performance and emissions deficit when a diesel engine is operated with biodiesel. There are research efforts to improve the diesel engine design to optimize the combustion with biodiesel. Since the common rail engines operates on flexible injection strategies, there exist an opportunity to improve engine performance and offset the fuel economy deficit by means of optimizing the engine control strategies. This approach may prove to be more practical and easily implemented. This study investigated the effects of the fuel injection parameters - rail pressure, injection duration and injection timing - on a common rail passenger car engine in terms of the fuel economy. Palm oil based biodiesel up to 30% blend in diesel was used in this study. The end of injection, (EOI), was found to be the most important parameter for affecting fuel consumption and thermal efficiency.

Reactivity controlled compression ignition and conventional diesel combustion: A comparison of methods to meet light-duty NOx and fuel economy targets

This study compares conventional diesel combustion and reactivity controlled compression ignition combustion in a light-duty engine at NOx levels equivalent to US Tier 2 Bin 5 and proposes a simple method to account for the added fluid consumption required to meet NOx constraints using aftertreatment. Reactivity controlled compression ignition and conventional diesel combustion are compared assuming that the conventional diesel combustion mode uses selective catalytic reduction to meet NOx constraints. The results show that reactivity controlled compression ignition is capable of meeting cycle-averaged NOx targets (equivalent to Tier 2 Bin 5) without NOx aftertreatment. In addition, efficiency comparisons show that reactivity controlled compression ignition offers a 4% improvement in fuel consumption and a 7.3% improvement in total fluid consumption (fuel + diesel exhaust fluid) over conventional diesel combustion with selective catalytic reduction. The fuel consumption improvement is due primarily to lower heat transfer losses. Additionally, it was found that the efficiency of reactivity controlled compression ignition can be further improved by careful selection of operating conditions and the combustion chamber configuration. The modeling shows that over 52% gross indicated efficiency can be achieved in the light-duty engine while meeting NOx targets in-cylinder.

Use of Low-Pressure Direct-Injection for Reactivity Controlled Compression Ignition (RCCI) Light-Duty Engine Operation

Use of Low-Pressure Direct-Injection for Reactivity Controlled Compression Ignition (RCCI) Light-Duty Engine Operation

Effect of Piston Bowl Geometry on Dual Fuel Reactivity Controlled Compression Ignition (RCCI) in a Light-Duty Engine Operated with Gasoline/Diesel and Methanol/Diesel

Effect of Piston Bowl Geometry on Dual Fuel Reactivity Controlled Compression Ignition (RCCI) in a Light-Duty Engine Operated with Gasoline/Diesel and Methanol/Diesel

Impact of alternative fuels on performance and pollutant emissions of a light duty engine tested under the new European driving cycle

Two alternative fuels, a gas to liquid (GTL) fuel from a low temperature Fischer–Tropsch process and a biodiesel produced from animal fats, have been tested using a light duty diesel engine with road load simulation (RLS) under the New European Driving Cycle (NEDC). The engine used has a variable geometry turbocharger (VGT), exhaust gas recirculation with cooling (EGR), common rail with split fuel injection and diesel oxidation catalyst (DOC). Regulated emissions have been evaluated and noticeable reductions in THC and CO were observed with both alternative fuels whereas only slight decrease was obtained in NOx emissions with biodiesel. With respect to results on particle matter, important reductions in both particle number and particle mass were obtained with both alternative fuels.

Effects of EGR, swirl augmentation techniques on combustion of biodiesel/ethanol and their blends in a diesel engine

The diminishing resources and continuously increasing cost of petroleum in association with their alarming pollution levels from diesel engines have caused an interest in finding alternative fuels to diesel which are renewable and sustainable. Emission control and engine efficiency are two most important parameters in current engine design. The impending introduction of emission standards such as Euro IV and Euro V is forcing the research towards developing new technologies for combating engine emissions. The classification of Euro IV and V norms is applicable to heavy-duty engines in Europe, where as Euro 5 is applicable to light-duty engines. This paper presents the effects of exhaust gas recirculation (EGR), swirl augmentation techniques and ethanol addition on the combustion of Honge oil methyl ester (HOME) and its blends with ethanol in a diesel engine. From the experimental work conducted, it is found that the combustion of HOME plus up to 15% ethanol blend in a diesel engine operated with optimised parameters of injection timing 23° Before Top Dead Centre and compression ratio 17.5 results in acceptable combustion emissions and improved brake thermal efficiency (BTE). The addition of ethanol increased BTE with reduced hydrocarbons (HCs), CO and smoke emissions. However, NO x emissions increased dramatically. Use of appropriate EGR reduces NO x to acceptable levels. The implementation of swirl augmentation techniques further resulted in increased BTE and considerable reduction in tail pipe emissions such as smoke, HCs, CO and NO x . The effect of swirl by providing grooves on the piston was taken into consideration to find the overall biodiesel engine performance, which gives scope for further studies.