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This paper gives a thorough review of the HC/CO emissions challenge and discusses the effects of different diesel oxidation catalyst designs in a pre turbine and post turbine position on steady state and transient turbo charger performance as well as on HC and CO tailpipe emissions, fuel economy and performance of modern Diesel engines. Results from engine dynamometer testing are presented. Both classical diffusive and advanced premixed Diesel combustion modes are investigated to understand the various effects of possible future engine calibration strategies.

Using a 3 liter, 4 valves per cylinder, V6 Diesel engine model, this study investigates late intake valve closing (LIVC) time in an effort to reduce the fuel consumption of the engine. Two different intake cam duration technologies for diesel engines are evaluated using a 1-D engine simulation software code. The first method utilized for duration control delays the effective closing of the intake valve by moving one intake cam lobe with respect to the other baseline intake cam lobe. In the second method, the closing of both intake valves is delayed by the introduction of an adjustable dwell period during the closing portion of the valve motion. During this mid-lift dwell period, the lift is held at a constant value until it goes into the closing phase. The systems are evaluated and compared at 4 operating points of varying engine speed and load. At each operating point, while engine load is held constant, intake valve closing time is varied.

A 1-D GT-Power model based investigation has been carried out to identify the impact of late intake valve closing (LIVC) on fuel economy and emission reduction of a modern small bore diesel engine. The diesel engine examined employed a variable turbine geometry (VTG) turbocharger with air-to-air charge cooler, cooled low pressure exhaust gas re-circulation (LP-EGR), and cooled high pressure exhaust gas re-circulation (HP-EGR). The LIVC system investigated varied the closing time of the intake valve by increasing or decreasing the dwell at the maximum valve lift point. This paper describes how the fuel economy and NOx emission of the diesel engine were affected by varying the intake valve closing time. The intake valve closing time was delayed by as much as 60 degrees.

The thermal management of vehicles has increased in importance due to the significant role of friction and auxiliary losses in engine operation on CO2 emissions. To evaluate different system and component concepts regarding their influence on fuel consumption, simulation offers a wide range of opportunities. In this paper a fully integrated model is presented utilizing the GT-Suite commercial code. It contains a diesel engine system model, a cooling circuit including a simplified model for the cooler package in the vehicle front end and a vehicle model. The purpose of this model is the investigation of cooling system components and control strategies with different engine inputs. A significant run time advantage is achieved by using a mean value engine model, which has a reduced number of input parameters. The simulation using the integrated model can be carried out within an acceptable time frame which enables vehicle drive cycle analysis.

Prior work with the concept of dividing the exhaust process into an early and late phase has shown the potential of applying only the early stage (blow-down) of the exhaust period directly to a turbocharger or turbocharger system, and the later stage (scavenge) arranged to bypass the turbine. In this manner, the exhaust backpressure required to extract high turbine work from the engine can be isolated from the displacement phase of the exhaust stroke and thereby greatly reduce the exhaust pumping work and Residual Gas Fraction. In previously-published efforts, the challenges of valve-event control and high turbine inlet temperature have been revealed. The BorgWarner Engine Systems Group, in conjunction with Presta, has applied a cam-phaser controlled concentric camshaft system to the exhaust side of a divided exhaust port 4-valve per cylinder DOHC GDI engine, to enable variable phasing between the Blow-down and Scavenge cam profiles.

It has been clearly demonstrated separately, that the application of both Dual Cam Phasers (DCP) and External Cooled EGR systems are highly beneficial to improving the efficiency of highly-boosted GDI engines. DCP systems can optimize the volumetric efficiency at WOT conditions, improve boost and transient response at low engine speeds, and provide internal EGR at low RPM part-load conditions. External cooled EGR has been demonstrated to dramatically improve the fuel consumption, lower turbine inlet temperature, and improve emissions at high power conditions. In previous investigations by the BorgWarner Engine Systems Group, we showed that full engine speed/load range EGR coverage can be obtained by combining High Pressure Loop and Low Pressure Loop external EGR systems with a DCP strategy.

In order to reduce nitrogen oxides (NOx) and soot emissions while maintaining high thermal efficiency, more advanced combustion concepts have been developed over the years, such as Homogeneous Charge Compression Ignition (HCCI) and Partially Premixed Combustion (PPC), as possible combustion processes in commercial engines. Compared to HCCI, PPC has advantages of lower unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions; however, due to increased fuel stratifications, soot emissions can be a challenge when adding Exhaust-Gas Recirculation (EGR) gas. The current work presents particle size distribution measurements performed from HCCI-like combustion with very early (120 CAD BTDC) to PPC combustion with late injection timing (11 CAD BTDC) at two intake oxygen rates, 21% and 15% respectively. Particle size distributions were measured using a differential mobility spectrometer DMS500.

Alternative fuels have been proposed as a means for future energy-secure and environmentally sustainable transportation. This review and benchmarking show that several of the alternative fuels (e.g. methanol, ethanol, higher alcohols, RME, HVO, DME, and biogas/CNG) work well with several different engine concepts such as conventional SI, DICI, and dual fuel, and with the emerging concepts HCCI, RCCI, and PPC. Energy consumption is in most cases similar to that of diesel or gasoline, with the exception of methanol and ethanol that use less energy, especially in SI engines. Tailpipe emissions of CO2 with respect to engine work output (tank-to-output shaft) can be reduced by more than 15% compared to a highly efficient gasoline SI engine, and are the lowest with CNG / lean-burn SI and with alcohols in several engine concepts. Alternative fuels are considered safe and in most cases are associated with reduced risk with respect to cancer and other health and environmental issues.

The concept of Partially Premixed Combustion (PPC) in internal combustion engines has shown to yield high gross indicated efficiencies, but at the expense of gas exchange efficiencies. Most of the experimental research on partially premixed combustion has been conducted on compression ignition engines designed to operate on diesel fuel and relatively high exhaust temperatures. The partially premixed combustion concept on the other hand relies on dilution with high exhaust gas recirculation (EGR) rates to slow down the combustion which results in low exhaust temperatures, but also high mass flows over cylinder, valves, ports and manifolds. A careful design of the gas exchange system, EGR arrangement and heat exchangers is therefore of utter importance. Experiments were performed on a heavy-duty, compression ignition engine using a fuel consisting of 80 volume % 95 RON service station gasoline and 20 volume % n-heptane.

Heat loss is one of the greatest energy losses in engines. More than half of the heat is lost to cooling media and exhaust losses, and they thus dominate the internal combustion engine energy balance. Complex processes affect heat loss to the cylinder walls, including gas motion, spray-wall interaction and turbulence levels. The aim of this work was to experimentally compare the heat transfer characteristics of a stepped-bowl piston geometry to a conventional re-entrant diesel bowl studied previously and here used as the baseline geometry. The stepped-bowl geometry features a low surface-to-volume ratio compared to the baseline bowl, which is considered beneficial for low heat losses. Speed, load, injection pressure, swirl level, EGR rate and air/fuel ratio (λ) were varied in a multi-cylinder light duty engine operated in conventional diesel combustion (CDC) mode.

An experiment was conducted to investigate the effect of charge stratification on the combustion phasing in a single cylinder, heavy duty (HD) compression ignition (CI) engine. To do this the start of injection (SOI) was changed from -180° after top dead centre (ATDC) to near top dead centre (TDC) during which CA50 (the crank angle at which 50% of the fuel energy is released) was kept constant by changing the intake temperature. At each SOI, the response of CA50 to a slight increase or decrease of either intake temperature or SOI were also investigated. Afterwards, the experiment was repeated with a different intake oxygen concentration. The results show that, for the whole SOI period, the required intake temperature to keep constant CA50 has a “spoon” shape with the handle on the -180° side.

In this paper, a parametric analysis on the main engine calibration parameters applied on gasoline Partially Premixed Combustion (PPC) is performed. Theoretically, the PPC concept permits to improve both the engine efficiencies and the NOx-soot trade-off simultaneously compared to the conventional diesel combustion. This work is based on the design of experiments (DoE), statistical approach, and investigates on the engine calibration parameters that might affect the efficiencies and the emissions of a gasoline PPC. The full factorial DoE analysis based on three levels and three factors (33 factorial design) is performed at three engine operating conditions of the Worldwide harmonized Light vehicles Test Cycles (WLTC). The pilot quantity (Qpil), the crank angle position when 50% of the total heat is released (CA50), and the exhaust gas recirculation (EGR) factors are considered. The goal is to identify an engine calibration with high efficiency and low emissions.

In this study, an investigation was made on a heavy duty diesel engine using both conventional diesel combustion mode and a partially premixed combustion (PPC) mode. A segment mesh was built up and modeled using the commercial CFD code AVL FIRE, where only the closed volume cycle, between IVC and EVO, was modeled. Both combustion modes were validated using experimental data, before a number of heat flux boundary conditions were applied. These conditions were used to evaluate the engine response in terms of engine performance and emission levels for the different percentage of heat rejection. The engine performance was measured in terms of specific fuel consumption and estimated power output, while the calculated net soot and accumulated NOx mass fractions were used for comparing the emission levels. The results showed improved efficiency for both combustion types, but only the PPC combustion mode managed that without increasing the production of NOx emissions severely.

Few previous publications investigate the possibility of combining multiple waste heat sources in a combustion engine waste heat recovery system. A waste heat recovery system for a HD truck diesel engine is evaluated for utilizing multiple heat sources found in a conventional HD diesel engine. In this type of engine more than 50% of heat energy goes futile. The majority of the heat energy is lost through engine exhaust and cooling devices such as EGRC (Exhaust gas recirculation cooler), CAC (Charge air cooler) and engine cooling. In this paper, the potential of usable heat recuperation from these devices using thermodynamic analysis was studied, and also an effort is made to recuperate most of the available heat energy that would otherwise be lost. A well-known way of recuperating this heat energy is by employing a Rankine cycle circuit with these devices as heat sources (single loop or dual loop), and thus this study is focused on using a Rankine cycle for the heat recovery system.

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions. The objective is to investigate the usefulness of negative valve overlap on a light duty diesel engine running with gasoline partially premixed combustion at low load operating conditions. The idea is to use negative valve overlap to trap hot residual gases to elevate the global in-cylinder temperature to promote auto-ignition of the high octane number fuel. This is of practical interest at low engine speed and load operating conditions because it can be assumed that the available boost is limited. The problem with NVO at low load operating conditions is that the exhaust gas temperature is low.

The impact of ignition quality and chemical properties on engine performance and emissions during low load partially premixed combustion (PPC) in a light-duty diesel engine were investigated. Four fuels in the gasoline boiling range, together with Swedish diesel (MK1), were operated at loads between 2 and 8 bar IMEPg at 1500 rpm, with 50% heat released located at 6 crank angle degrees (CAD) after top dead center (TDC). A single injection strategy was used, wherein the start of injection (SOI) and the injection duration were adjusted to achieve desired loads with maintained CA50, as the injection pressure was kept constant at 1000 bar. The objective of this work was to examine the low-load limit for PPC at approximately 50% EGR and λ=1.5, since these levels had been suggested as optimal in earlier studies. The low-load limits with stable combustion were between 5 and 7 bar gross IMEP for the gasoline fuels, higher limit for higher RON values.

Partially Premixed Combustion (PPC) has the potential of simultaneously providing high engine efficiency and low emissions. Previous research has shown that with proper combination of Exhaust-Gas Recirculation (EGR) and Air-Fuel equivalence ratio, it is possible to reduce engine-out emissions while still keeping the engine efficiency high. In this paper, the effect of changes in intake pressure (boost) and EGR fraction on PPC engine performance (e.g. ignition delay, burn duration, maximum pressure rise rate) and emissions (carbon monoxide (CO), unburned hydrocarbon (UHC), soot and NOX) was investigated in a single-cylinder, heavy-duty diesel engine. Swedish diesel fuel (MK1), RON 69 gasoline fuel and 99.5 vol% ethanol were tested. Fixed fueling rate and single injection strategy were employed.

Partially Premixed Combustion (PPC) has demonstrated substantially higher efficiency compared to conventional diesel combustion (CDC) and gasoline engines (SI). By combining experiments and modeling the presented work investigates the underlying reasons for the improved efficiency, and quantifies the loss terms. The results indicate that it is possible to operate a HD-PPC engine with a production two-stage boost system over the European Stationary Cycle while likely meeting Euro VI and US10 emissions with a peak brake efficiency above 48%. A majority of the ESC can be operated with brake efficiency above 44%. The loss analysis reveals that low in-cylinder heat transfer losses are the most important reason for the high efficiencies of PPC. In-cylinder heat losses are basically halved in PPC compared to CDC, as a consequence of substantially reduced combustion temperature gradients, especially close to the combustion chamber walls.

A better understanding of turbulent kinetic energy is important for improvement of fuel-air mixing, which can lead to lower emissions and reduced fuel consumption. An in-cylinder flow study was conducted using 1548 Laser Doppler Velocimetry (LDV) measurements inside one cylinder of a 3.5L four-valve engine. The measurement method, which simultaneously collects three-dimensional velocity data through a quartz cylinder, allowed a volumetric evaluation of turbulent kinetic energy (TKE) inside an automotive engine. The results were animated on a UNIX workstation, using a 3D wireframe model. The data visualization software allowed the computation of TKE isosurfaces, and identified regions of higher turbulence within the cylinder. The mean velocity fields created complex flow patterns with symmetries about the center plane between the two intake valves. High levels of TKE were found in regions of high shear flow, attributed to the collisions of intake flows.

Partially Premixed Combustion, PPC, with 50% Exhaust Gas Recirculation (EGR) at lean combustion conditions λ =1.5, has shown good efficiency and low emissions in a heavy-duty single-cylinder engine. To meet emission requirements in all loads and transient operation, aftertreatment devices are likely needed. Reducing λ to unity, when a three-way catalyst can be applied, extremely low emissions possibility exists for stoichiometric PPC. In this study, the possibility to operate clean PPC from lean condition to stoichiometric equivalence ratio with reasonable efficiency and non-excessive soot emission was investigated. Two EGR rates, 48% and 38% with two fuel rates were determined for 99.5 vol% ethanol in comparison with one gasoline fuel and Swedish diesel fuel (MK1). Engine was operated at 1250 rpm and 1600 bar injection pressure with single injection. Results revealed that efficiency was reduced and soot emission increased from lean PPC to stoichiometric PPC operation.