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Partially Premixed Combustion (PPC) is used to meet the increasing demands of emission legislation and to improve fuel efficiency. PPC with gasoline fuels have the advantage of a longer premixed duration of fuel/air mixture which prevents soot formation at higher loads. The objective of this paper is to investigate the degree of stratification for low load (towards idle) engine conditions using different injection strategies and negative valve overlap (NVO). The question is, how homogenous or stratified is the partially premixed combustion (PPC) for a given setting of NVO and fuel injection strategy. In this work PRF 55 has been used as PPC fuel. The experimental engine is a light duty (LD) diesel engine that has been modified to single cylinder operation to provide optical access into the combustion chamber, equipped with a fully variable valve train system. Hot residual gases were trapped by using NVO to dilute the cylinder mixture.

Internal combustion engine (ICE) fuel efficiency is a balance between good indicated efficiency and mechanical efficiency. High indicated efficiency is reached with a very diluted air/fuel-mixture and high load resulting in high peak cylinder pressure (PCP). On the other hand, high mechanical efficiency is obtained with very low peak cylinder pressure as the piston rings and bearings can be made with less friction. This paper presents studies of a combustion engine which consists of a two stage compression and expansion cycle. By splitting the engine into two different cycles, high-pressure (HP) and low-pressure (LP) cycles respectively, it is possible to reach high levels of both indicated and mechanical efficiency simultaneously. The HP cycle is designed similar to today's turbo-charged diesel engine but with an even higher boost pressure, resulting in high PCP. To cope with high PCP, the engine needs to be rigid.

In order to further improve the energy conversion efficiency in reciprocating engines, detailed knowledge about the involved processes is required. One major loss source in internal combustion engines is heat loss through the cylinder walls. In order to increase the understanding of heat transfer processes and to validate and generate new heat transfer correlation models it is desirable, or even necessary, to have crank-angle resolved data on in-cylinder wall temperature. Laser-Induced Phosphorescence has proved to be a useful tool for surface thermometry also in such harsh environments as running engines. However, the ceramic structure of most phosphor coatings might introduce an error, due to its thermal insulation properties, when being exposed to rapidly changing temperatures. In this article the measurement technique is evaluated concerning the impact from the thickness of the phosphorescent layer on the measured temperature.

The Technical University of Denmark, DTU, has designed, built and tested a gasifier [1, 8] that is fuelled with wood chips and achieves a 93% conversion efficiency from wood to producer gas. By combining the gasifier with an ICE and an electric generator a co-generative system can be realized that produces electricity and heat. The gasifier uses the waste heat from the engine for drying and pyrolysis of the wood chips while the gas produced is used to fuel the engine. To achieve high efficiency in converting biomass to electricity an engine is needed that is adapted to high efficiency operation using the specific producer gas from the DTU gasifier. So far the majority of gas engines have been designed and optimized for operation on natural gas. The presented work uses a modern and highly efficient truck sized natural gas engine to investigate efficiency, emissions and general performance while operating on producer gas compared to natural gas operation.

Low temperature combustion modes, such as Homogeneous Charge Compression Ignition (HCCI) and Partially Premixed Combustion (PPC), have been researched over recent decades since the concepts show promise for high efficiency and low emissions compared to conventional diesel combustion. PPC is an intermediate combustion type ranging from HCCI-like combustion to diesel-like combustion. The purpose of this paper is to study optically how the combustion and ignition are affected by different start of injection (SOI) timings. The study is carried out in an optically accessible heavy-duty single-cylinder engine with swirl. The intake pressure was kept constant while the intake temperature was varied to keep the combustion phasing (CA50) constant at ∼3 CAD atdc during an SOI sweep. The fuel used is a mix of primary reference fuels with octane number 81. To determine where the combustion starts, high-speed combustion imaging is used to detect the natural luminosity.

In recent years, stricter regulations on emissions and higher demands for more fuel efficient vehicles have led to a greater focus on increasing the efficiency of the internal combustion engine. Nowadays, there is increasing interest in the recovery of waste heat from different engine sources such as the coolant and exhaust gases using, for example, a Rankine cycle. In diesel engines 15% to 30% of the energy from the fuel can be lost to the coolant and hence, does not contribute to producing work on the piston. This paper looks at reducing the heat losses to the coolant by increasing coolant temperatures within a single cylinder Scania D13 engine and studying the effects of this on the energy balance within the engine as well as the combustion characteristics. To do this, a GT Power model was first validated against experimental data from the engine.

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.

The Technical University of Denmark, DTU, has constructed, built and tested a gasifier [1, 11] that is fueled with wood chips and achieves a 93% conversion efficiency from wood to producer gas. By combining the gasifier with an internal combustion engine and a generator, a co-generative system can be realized that produces electricity and heat. The gasifier uses the waste heat from the engine for drying and pyrolysis of the wood chips while the produced gas is used to fuel the engine. To achieve high efficiency in converting biomass to electricity it necessitates an engine that is adapted to high efficiency operation using the specific producer gas from the DTU gasifier. So far the majority of gas engines of today are designed and optimized for SI-operation on natural gas.

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 (PPC) is intended to improve fuel efficiency and minimize the engine-out emissions. PPC is known to have the potential to reduce emissions of nitrogen oxides (NOx) and soot, but often at the expense of increased emissions of unburned hydrocarbons (HC) and carbon monoxide (CO). PPC has demonstrated remarkable fuel flexibility and can be operated with a large variety of liquid fuels, ranging from low-octane, high-cetane diesel fuels to high-octane gasolines and alcohols. Several research groups have demonstrated that naphtha fuels provide a beneficial compromise between functional load range and low emissions. To increase the understanding of the influence of individual fuel components typically found in commercial fuels, such as alkenes, aromatics and alcohols, a systematic experimental study of 15 surrogate fuel mixtures of n-heptane, isooctane, toluene and ethanol was performed in a light-duty PPC engine using a design of experiment methodology.

In the quest for efficiency improvement in heavy duty truck engines, waste heat recovery could play a valuable role. The evaporative cycle is a waste heat recovery technology aimed at improving efficiency and decreasing emissions. A humid air motor (HAM) uses the waste heat from the exhaust of the engine to humidify the inlet air; this humid air, with higher specific heat, reduces NOx emission to a greater extent [1] [2]. Despite this benefit of emission reduction, the increase or decrease in efficiency of the humid air motor compared to the conventional engine is not discussed in the literature [3] [4] [5]. In this paper, an attempt is made to study the efficiency of the HAM using system model simulations of a 13-liter heavy duty Volvo engine with a humidifier. The commercial software GT-SUITE is used to build the system model and to perform the simulations. The efficiency improvement of the HAM comes from the expansion of the vapor mass flow produced as a result of humidification.

In the truck industry there is a continuous demand to increase the efficiency and to decrease the emissions. To acknowledge both these issues a waste heat recovery system (WHR) is combined with a partially premixed combustion (PPC) engine to deliver an efficient engine system. Over the past decades numerous attempts to increase the thermal efficiency of the diesel engine has been made. One such attempt is the PPC concept that has demonstrated potential for substantially increased thermal efficiency combined with much reduced emission levels. So far most work on increasing engine efficiency has been focused on improving the thermal efficiency of the engine while WHR, which has an excellent potential for another 1-5 % fuel consumption reduction, has not been researched that much yet. In this paper a WHR system using a Rankine cycle has been developed in a modeling environment using IPSEpro.

Partially premixed combustion (PPC) in internal combustion engine as a low temperature combustion strategy has shown great potential to achieve high thermodynamic efficiency. Methanol due to its unique properties is considered as a preferable PPC engine fuel. The injection timing to achieve methanol PPC conditions should be set very close to TDC, allowing to utilize spray-bowl interaction to further improve combustion process in terms of emissions and heat losses. In this study CFD simulations are performed to investigate spray-bowl interaction for a number of different piston designs and its impact on the heat transfer and the overall piston performance. The validation case is based on a single cylinder heavy-duty Scania D13 engine with a compression ratio 15. The operation point is set to low load 5.42 IMEPg bar with SOI -3 aTDC.

Partially premixed combustion (PPC) is an advanced combustion strategy that has been proposed to provide higher efficiency and lower emissions than conventional compression ignition, as well as greater controllability than homogeneous charge compression ignition (HCCI). Stratification of the fuel-air mixture is the key to achieving these benefits. The injection strategy, injector-piston geometry design and fuel properties are factors commonly manipulated to adjust the stratification level. In the authors’ previous research, the effects of injection strategy and fuel properties on the stratification formation process were investigated. The results revealed that, for a direct-injection compression ignition engine, by sweeping the injection timing from −180° aTDC (after top dead center) to −20° aTDC, the sweep could be divided into three different regimes: an HCCI regime, a Transition regime and a PPC regime, based on the changing of mixture stratification conditions.

Heat transfer losses are one of the largest loss contributions in a modern internal combustion engine. The aim of this study is to evaluate the contribution of the piston bowl type and swirl ratio to heat losses and performance. A commercial CFD tool is used to carry out simulations of four different piston bowl geometries, at three engine loads with two different swirl ratios at each load point. One of the geometries is used as a reference point, where CFD results are validated with engine test data. All other bowl geometries are scaled to the same compression ratio and make use of the same fuel injection, with a variation in the spray target between cases. The results show that the baseline case, which is of a conventional diesel bowl shape, provides the best emission performance, while a more open, tapered, lip-less combustion bowl is the most thermodynamically efficient.

Humid air motor (HAM) is an engine operated with humidified inlet charge. System simulations study on HAM showed the waste heat recovery potential over a conventional system. An HAM setup was constructed, to comprehend the potential benefits in real-time, the HAM setup was built around a 13-litre six cylinder Volvo diesel engine. The HAM engine process is explained in detail in this paper. Emission analysis is also performed for all three modes of operation. The experiments were carried out at part load operating point of the engine to understand the effects of humidified charge on combustion, efficiency, and emissions. Experiments were conducted without EGR, with EGR, and with humidified inlet charge. These three modes of operation provided the potential benefits of each system. Exhaust heat was used for partial humidification process. Results show that HAM operation, without compromising on efficiency, reduces NOx and soot significantly over the engine operated without EGR.