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Pre-chamber spark ignition (PCSI) combustion is an emerging lean-burn combustion mode capable of extending the lean operation limit of an engine. The favorable characteristic of short combustion duration at the lean condition of PCSI results in high efficiencies compared to conventional spark ignition combustion. Since the engine operation is typically lean, PCSI can significantly reduce engine-out NOx emissions while maintaining short combustion durations. In this study, experiments were conducted on a heavy-duty engine at lean conditions at mid to low load. Two major studies were performed. In the first study, the total fuel energy input to the engine was fixed while the intake pressure was varied, resulting in varying the global excess air ratio. In the second study, the intake pressure was fixed while the amount of fuel was changed to alter the global excess air ratio.

Partially Premixed Combustion (PPC) provides the potential of simultaneous reduction of NOx and soot for diesel engines. This work attempts to characterize the operating range and conditions required for PPC. The characterization is based on the evaluation of emission and in-cylinder measurement data of engine experiments. It is shown that the combination of low compression ratio, high EGR rate and engine operation close to stoichiometric conditions enables simultaneous NOx and soot reduction at loads of 8bar, 12bar, and 15bar IMEP gross. The departure from the conventional NOx-soot trade-off curve has to be paid with a decline in combustion efficiency and a rise in HC and CO emissions. It is shown that the low soot levels of PPC come along with long ignition delay and low combustion temperature. A further result of this work is that higher inlet pressure broadens the operating range of Partially Premixed Combustion.

An estimation model which uses the gross heat release data and the fuel energy to estimate the total amount of emissions and unburned Hydro Carbon (HC) is developed. Gross heat release data is calculated from a self-tuned heat release method which uses in-cylinder pressure data for computing the energy released during combustion. The method takes all heat and mass losses into account. The method estimates the polytropic exponent and pressure offset during compression and expansion using a nonlinear least square method. Linear interpolation of polytropic exponent and pressure offset is then performed during combustion to calculate the gross heat release during combustion. Moreover the relations between the emissions specifically HC and Carbon Monoxide (CO) are investigated. The model was validated with experimental data and promising results were achieved.

A multi-zone model has been developed that accurately predicts HCCI combustion and emissions. The multi-zone methodology is based on the observation that turbulence does not play a direct role on HCCI combustion. Instead, chemical kinetics dominates the process, with hotter zones reacting first, and then colder zones reacting in rapid succession. Here, the multi-zone model has been applied to analyze the effect of piston crevice geometry on HCCI combustion and emissions. Three different pistons of varying crevice size were analyzed. Crevice sizes were 0.26, 1.3 and 2.1 mm, while a constant compression ratio was maintained (17:1). The results show that the multi-zone model can predict pressure traces and heat release rates with good accuracy. Combustion efficiency is also predicted with good accuracy for all cases, with a maximum difference of 5% between experimental and numerical results.

Homogenous Charge Compression Ignition (HCCI) is a promising part load combustion concept for future power train applications. Different approaches to achieve and control HCCI combustion are today investigated and compared, especially concerning operating range. The HCCI operating range for vehicle applications should at least cover contemporary emissions drive cycles. The operating range in terms of speed and load is investigated with a Naturally Aspirated (NA) four-stroke multi-cylinder engine with Port Fuel Injection (PFI). HCCI combustion control is achieved with Variable Compression Ratio (VCR) and inlet air preheating with exhaust heat. Both primary reference fuels and commercial gasoline are used in the tests. HCCI combustion with commercial gasoline is achieved over a load range from 0 to 3.6bar BMEP, and over a speed range from 1000 to 5000rpm. Maximum load is at 1000rpm and decreases with an approximately straight slope to zero at 5000rpm.

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.

Low temperature combustion concepts are studied recently to simultaneously reduce NOX and soot emissions. Optical studies are performed to study gasoline PPC in CI engines to investigate in-cylinder combustion and stratification. It is imperative to perform emission measurements and interpret the results with combustion images. In this work, we attempt to investigate this during the transition from CI to HCCI mode for FACE I gasoline (RON = 70) and its surrogate, PRF70. The experiments are performed in a single cylinder optical engine that runs at a speed of 1200 rpm. Considering the safety of engine, testing was done at lower IMEP (3 bar) and combustion is visualized using a high-speed camera through a window in the bottom of the bowl. From the engine experiments, it is clear that intake air temperature requirement is different at various combustion modes to maintain the same combustion phasing.

In-cylinder visualization, combustion stratification, and engine-out particulate matter (PM) emissions were investigated in an optical engine fueled with Haltermann straight-run naphtha fuel and corresponding surrogate fuel. The combustion mode was transited from homogeneous charge compression ignition (HCCI) to conventional compression ignition (CI) via partially premixed combustion (PPC). Single injection strategy with the change of start of injection (SOI) from early to late injections was employed. The high-speed color camera was used to capture the in-cylinder combustion images. The combustion stratification was analyzed based on the natural luminosity of the combustion images. The regulated emission of unburned hydrocarbon (UHC), carbon monoxide (CO) and nitrogen oxides (NOX) were measured to evaluate the combustion efficiency together with the in-cylinder rate of heat release.

The literature study on PPC in optical engine reveals investigations on OH chemiluminescence and combustion stratification. So far, mostly PRF fuel is studied and it is worthwhile to examine the effect of fuel properties on PPC. Therefore, in this work, fuel having different octane rating and physical properties are selected and PPC is studied in an optical engine. The fuels considered in this study are diesel, heavy naphtha, light naphtha and their corresponding surrogates such as heptane, PRF50 and PRF65 respectively. Without EGR (Intake O2 = 21%), these fuels are tested at an engine speed of 1200 rpm, fuel injection pressure of 800 bar and pressure at TDC = 35 bar. SOI is changed from late to early fuel injection timings to study PPC and the shift in combustion regime from CI to PPC is explored for all fuels. An increased understanding on the effect of fuel octane number, physical properties and chemical composition on combustion and emission formation is obtained.

Light naphtha is the light distillate from crude oil and can be used in compression ignition (CI) engines; its low boiling point and octane rating (RON = 64.5) enable adequate premixing. This study investigates the combustion characteristics of light naphtha (LN) and its multicomponent surrogate under various start of injection (SOI) conditions. LN and a five-component surrogate for LN, comprised of 43% n-pentane, 12% n-heptane, 10% 2-methylhexane, 25% iso-pentane and 10% cyclo-pentane, has been tested in a single cylinder optical diesel engine. The transition in combustion homogeneity from CI combustion to homogenized charge compression ignition (HCCI) combustion was then compared between LN and its surrogate. The engine experimental results showed good agreement in combustion phasing, ignition delay, start of combustion, in-cylinder pressure and rate of heat release between LN and its surrogate.

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) 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.

HCCI combustion can be enabled by many types of liquid and gaseous fuels. When considering what fuels will be most suitable, the emissions also have to be taken into account. This study focuses on the emissions formation originating from different fuel components. A systematic study of over 40 different gasoline surrogate fuels was made. All fuels were studied in a CFR engine running in HCCI operation. Many of the fuels were blended to achieve similar RON's and MON's as gasoline fuels, and the components (n-heptane, iso-octane, toluene, and ethanol) were chosen to represent the most important in gasoline; nparaffins, iso-paraffins, aromatics and oxygenates. The inlet air temperature was varied from 50°C to 150°C to study the effects on the emissions. The compression ratio was adjusted for each operating point to achieve combustion 3 degrees after TDC. The engine was run at an engine speed of 600 rpm, with ambient intake air pressure and with an equivalence ratio of 0.33.

A FeCrAlloy mesh-type catalyst has been used to reduce hydrocarbons (HC) and carbon monoxide (CO) emissions from a 4-stroke HCCI engine. Significant for the HCCI engine is a high compression ratio and lean mixtures, which leads to a high efficiency, low combustion temperatures and thereby low NOx emissions, <5 pmm, but also low exhaust temperatures, around 300°C. It becomes critical to: 1. Ensure that the HCCI-combustion generates as low HC emissions as possible, this can be done by very precise control of engine inlet conditions and, if possible, compression ratio. 2. Ensure that the exhaust temperature is high enough, without loosing efficiency or producing NOx; in order to get an oxidizing catalyst to work. 3. Select proper catalyst material for the catalyst so that the exhaust temperature can be as low as possible.

Homogeneous Charge Compression Ignition (HCCI) combustion is a process dominated by chemical kinetics of the fuel-air mixture. The hottest part of the mixture ignites first, and compresses the rest of the charge, which then ignites after a short time lag. Crevices and boundary layers generally remain too cold to react, and result in substantial hydrocarbon and carbon monoxide emissions. Turbulence has little effect on HCCI combustion, and may be most important as a factor in determining temperature gradients and boundary layer thickness inside the cylinder. The importance of thermal gradients inside the cylinder makes it necessary to use an integrated fluid mechanics-chemical kinetics code for accurate predictions of HCCI combustion. However, the use of a fluid mechanics code with detailed chemical kinetics is too computationally intensive for today's computers.

The use of water injection in a Homogeneous Charge Compression Ignition (HCCI) engine was experimentally investigated. The purpose of this study was to examine whether it is possible to control the ignition timing and slow down the rate of combustion with the use of water injection. The effects of different water flows, air/fuel ratios and inlet pressures were studied for three different fuels, iso-octane, ethanol and natural gas. It is possible to control the ignition timing in a narrow range with the use of water injection, but to the prize of an increase in the already high emissions of unburned hydrocarbons. The CO emission also increased. The NOx emissions, which are very low for HCCI, decreased even more when water injection was applied. The amount of water used was of the magnitude of the fuel flow.

Partially premixed combustion (PPC) is a promising way to achieve high efficiency and low engine-out emissions simultaneously in a heavy-duty engine. Compared to Homogeneous Charge Compression Ignition (HCCI), it can be controlled by injection events and much lower HC and CO emissions can be achieved. This work focuses on the transition from HCCI to PPC and combustion and emissions characteristics during the process are investigated. Injection strategies, EGR and boost pressure were the main parameters used to present the corresponding effect during the transition.

Partially premixed combustion (PPC) is a low-temperature combustion concept that could deliver higher engine efficiency, as well as lower emissions. Gasoline-like fuel compression ignition (GCI) is beneficial for air/fuel mixing process under PPC mode because of the superior auto-ignition resistance to prolong ignition delay time. In current experiments, three surrogate fuels with same research octane number (RON77) but different octane sensitivities (OS), PRF77 (S = 0), TPRF77-a (S = 3) and TPRF77-b (S = 5), are tested in a full-transparent single cylinder AVL optical compression ignition (CI) engine at low load conditions. Aiming at investigating the fuel octane sensitivity effect on engine combustion behavior as well as emissions under GCI-PPC mode, engine parameters, and emission data during combustion are compared for the test fuels with a change of injection timing.

In the engine community, gasoline compression ignition (GCI) engines are at the forefront of research and efforts are being taken to commercialize an optimized GCI engine in the near future. GCI engines are operated typically at Partially Premixed Combustion (PPC) mode as it offers better control of combustion with improved combustion stability. While the transition in combustion homogeneity from convectional Compression Ignition (CI) to Homogenized Charge Compression Ignition (HCCI) combustion via PPC has been comprehensively investigated, the physical and chemical effects of fuel on GCI are rarely reported at different combustion modes. Therefore, in this study, the effect of physical and chemical properties of fuels on GCI is investigated. In-order to investigate the reported problem, low octane gasoline fuels with same RON = 70 but different physical properties and sensitivity (S) are chosen.