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In response to global climate change, there is a widespread push to reduce carbon emissions in the transportation sector. For the difficult to decarbonize heavy-duty (HD) vehicle sector, lower carbon intensity fuels can offer a low-cost, near-term solution for CO2 reduction. The use of natural gas can provide such an alternative for HD vehicles while the increasing availability of renewable natural gas affords the opportunity for much deeper reductions in net-CO2 emissions. With this in consideration, the US National Renewable Energy Laboratory launched the Natural Gas Vehicle Research and Development Project to stimulate advancements in technology and availability of natural gas vehicles. As part of this program, Southwest Research Institute developed a hybrid-electric medium-HD vehicle (class 6) to demonstrate a substantial CO2 reduction over the baseline diesel vehicle and ultra-low NOx emissions.

Low temperature combustion (LTC) modes are among the advanced combustion technologies which offer thermal efficiencies comparable to conventional diesel combustion and produce ultra-low NOx and particulate matter (PM) emissions. However, combustion timing control, excessive pressure rise rate and high cyclic variations are the common challenges encountered by the LTC modes. These challenges can be addressed by developing model-based control framework for the LTC engine. In the current study, in-cylinder pressure data for dual-fuel LTC engine operation is analyzed for 636 different operating conditions and the heat release rate (HRR) traces are classified into three distinct classes based on their distinct shapes. These classes are named as Type-1, Type-2 and Type-3, respectively.

This research investigates the energy savings achieved through eco-driving controls in connected and automated vehicles (CAVs), with a specific focus on the influence of powertrain characteristics. Eco-driving strategies have emerged as a promising approach to enhance efficiency and reduce environmental impact in CAVs. However, uncertainty remains about how the optimal strategy developed for a specific CAV applies to CAVs with different powertrain technologies, particularly concerning energy aspects. To address this gap, on-track demonstrations were conducted using a Chrysler Pacifica CAV equipped with an internal combustion engine (ICE), advanced sensors, and vehicle-to-infrastructure (V2I) communication systems, compared with another CAV, a previously studied Chevrolet Bolt electric vehicle (EV) equipped with an electric motor and battery.

Engine knock is one of the limiting factors in determining the compression ratio and engine efficiency for spark ignited engines. Using the Southwest Research Institute Knock-CoV test method, it was previously shown that the knock limited load versus combustion phasing (CA50) has a constant slope. All of the knock mitigation strategies tested provided a shift to these knock limited loads but also increased the slope. That is, for the same CA50 retard the knock limited load could be increased more. Our hypothesis was that due to fuel sensitivity, or the difference between the RON and MON, the reactions that lead to knock will behave differently as the pressure-temperature history changes with engine speeds and loads. The fuel affects on the knock and CoV limits were studied by testing fuels with various sensitivities including methanol, E85 (85% ethanol) and Iso-octane.

Water injection has been used to reduce the charge temperature and mitigate knocking due to its higher latent heat of vaporization compared to gasoline fuel. When water is injected into the intake manifold or into the cylinder, it evaporates by absorbing heat energy from the surrounding and results in charge cooling. However, the effect of detailed evaporation process on the combustion characteristics under gasoline direct injection relevant conditions still needs to be investigated. Therefore, spray study was firstly conducted using a multi-hole injector by injecting pure water and water-methanol mixture into constant volume combustion chamber (CVCC) at naturally aspirated and boosted engine conditions. The target water-fuel ratio was fixed at 0.5. Mie-scattering and schlieren images of sprays were analyzed to study spray characteristics, and evaluate the amount of water vaporization.

The medium and heavy-duty powertrain industry trend is to reduce reliance on diesel fuel and is aligned with continued efforts of achieving ultra-low emissions and high brake efficiencies. Compression Ignition (CI) of late cycle Directly Injected (DI) Natural Gas (NG) shows the potential to match diesel performance in terms of brake efficiency and power density, with the benefit of utilizing a lower carbon content fuel. A primary challenge is to achieve stable ignition of directly injected NG over a wide engine speed and load range without the need for a separate ignition source. This project aims to demonstrate the CI of DI NG through experimental studies with a Single Cylinder Research Engine (SCRE), leading to the development of a mono-fueled NG engine with equivalent performance to that of current diesel technology, 25% lower CO2 emissions, and low engine out methane emissions.

The automotive sector is rapidly transitioning to decarbonized, electric vehicles solutions. However, due to challenges with such rapid adoption, Internal combustion engines (ICE) are expected to be used for decades to come. In this transition period it is important to continue to improve ICE efficiency. A key design parameter to increase ICE efficiency is the compression ratio. For gasoline engines, the compression ratio is limited so as to avoid knock. Engine designers can employ several strategies to mitigate knock and enable higher compression ratios. In this study, a new methodology has been developed to compare various knock mitigation strategies. By comparing the knock limited load at a given combustion phasing the expected compression ratio increase can be inferred.

The increase in regulatory demand to reduce CO2 emissions resulted in a focus on the development of novel combustion modes such as gasoline compression ignition (GCI). It has been shown by others that GCI can improve the overall engine efficiency while achieving soot and NOx emissions targets. In comparison with diesel fuel, gasoline has a higher volatility and has more resistance to autoignition, therefore, it has a longer ignition delay time which facilitates better mixing of the air-fuel charge before ignition. In this study, a GCI combustion system has been tested using a 2.2L compression ignition engine as part of a US Department of Energy funded project. For this purpose, a multiple injection strategy was developed to improve the pressure rise rates and soot emission levels for the same engine out NOx emissions.

A diesel piloted natural gas engine's performance varies depending on operating conditions and has performed best under medium to high loads. It can often equal or better the fuel conversion efficiency of a diesel-only engine in this operating range. This paper presents a study performed on a multi-cylinder Cummins ISB 6.7L diesel engine converted to run stoichiometric natural gas/diesel micro-pilot combustion with a maximum diesel contribution of 10%. This study systematically quantifies and ranks the sensitivity of control factors on combustion and performance while operating at medium loads. The effects of combustion control parameters, including the pilot start of injection, pilot injection pressure, pilot injection quantity, exhaust gas recirculation, and global equivalence ratio, were tested using a design of experiments orthogonal matrix approach.

As the world searches for ways to reduce humanity’s impact on the environment, the automotive industry looks to extend the viable use of the gasoline engine by improving efficiency. One way to improve engine efficiency is through more effective control. Torque-based control is critical in modern cars and trucks for traction control, stability control, advanced driver assistance systems, and autonomous vehicle systems. Closed loop torque-based engine control systems require feedback signal(s); indicated mean effective pressure (IMEP) is a useful signal but is costly to measure directly with in-cylinder pressure sensors. Previous work has been done in torque and IMEP estimation using crankshaft acceleration and ion sensors, but these systems lack accuracy in some operating ranges and the ability to estimate cycle-cycle variation.

The dedicated exhaust gas recirculation (D-EGR®) concept developed by Southwest Research Institute (SwRI) has demonstrated a thermal efficiency increase on several spark-ignited engines at both low and high-load conditions. Syngas (H2+CO) is produced by the dedicated cylinder (D-cyl) which operates at a rich air-fuel ratio. The syngas helps to stabilize combustion under highly dilute conditions at low loads as well as mitigating knock at high loads. The D-cyl produces all the EGR for the engine at a fixed rate of approximately 25% EGR for a four-cylinder engine and 33% EGR for a six-cylinder engine. The D-cyl typically runs up to an equivalence ratio of 1.4 for gasoline-fueled engines, beyond which the combustion becomes unstable due to the decreasing laminar burning velocity caused by rich conditions. Conventional active-fueled and passive pre-chambers have benefits of inducing multi-site ignition and enhancing turbulence in the main chamber.

This paper presents a combined numerical and experimental investigation of the characteristics of spark discharge in a spark-ignition engine. The main objective of this work is to gain insights into the spark discharge process and early flame kernel development. Experiments were conducted in an inert medium within an optically accessible constant-volume combustion vessel. The cross-flow motion in the vessel was generated using a previously developed shrouded fan. Numerical modeling was based on an existing discharge model in the literature developed by Kim and Anderson. However, this model is applicable to a limited range of gas pressures and flow fields. Therefore, the original model was evaluated and improved to predict the behavior of spark discharge at pressurized conditions up to 45 bar and high-speed cross-flows up to 32 m/s. To accomplish this goal, a parametric study on the spark channel resistance was conducted.

The study of spray-wall interaction is of great importance to understand the dynamics that occur during fuel impingement onto the chamber wall or piston surfaces in internal combustion engines. It is found that the maximum spreading length of an impinged droplet can provide a quantitative estimation of heat transfer and energy transformation for spray-wall interaction. Furthermore, it influences the air-fuel mixing and hydrocarbon and particle emissions at combusting conditions. In this paper, an analytical model of a single diesel droplet impinging on the wall with different inclined angles (α) is developed in terms of βm (dimensionless maximum spreading length, the ratio of maximum spreading length to initial droplet diameter) to understand the detailed impinging dynamic process.

Past experimental studies conducted by the current authors on a 13 liter 16.7:1 compression ratio heavy-duty diesel engine have shown that diesel-Compressed Natural Gas (CNG) Reactivity Controlled Compression Ignition (RCCI) combustion targeting low NOx emissions becomes progressively difficult to control as the engine load is increased. This is mainly due to difficulty in controlling reactivity levels at higher loads. For the current study, CFD investigations were conducted in CONVERGE using the SAGE combustion solver with the application of the Rahimi mechanism. Studies were conducted at a load of 5 bar BMEP to validate the simulation results against RCCI experimental data. In the low load study, it was found that the Rahimi mechanism was not able to predict the RCCI combustion behavior for diesel injection timings advanced beyond 30 degCA bTDC. This poor prediction was found at multiple engine speed and load points.

Gasoline compression ignition (GCI) technology shows the potential to obtain high thermal efficiencies while maintaining low soot and NOx emissions in light-duty engine applications. Recent experimental studies and numerical simulations have indicated that high reactivity gasoline-like fuels can further enable the benefits of GCI combustion. However, there is limited empirical data in the literature studying the gasoline compression ignition process at relevant in-cylinder conditions, which are required for further optimizing combustion system designs. This study investigates the temporal and spatial evolution of the compression ignition process of various high reactivity gasoline fuels with research octane numbers (RON) of 71, 74 and 82, as well as a conventional RON 97 E10 gasoline fuel. A ten-hole prototype gasoline injector specifically designed for GCI applications capable of injection pressures up to 450 bar was used.

Dedicated exhaust gas recirculation (D-EGR®) concept developed by Southwest Research Institute (SwRI) has demonstrated a thermal efficiency increase on many spark-ignited engines at both low and high load conditions. The syngas (H2+CO) produced in the dedicated cylinder (D-cyl) by rich combustion helps to stabilize combustion at highly dilute conditions at low loads and mitigate knock at high loads. The dedicated cylinder with 25% EGR can typically run up to equivalence ratio of 1.4, beyond which the combustion becomes unstable. By injecting fresh air near the spark plug gap at globally rich conditions, a locally lean or near-stoichiometric mixture can be achieved, thus facilitating the ignitability of the mixture and increasing combustion stability. With more stable combustion a richer global mixture can be introduced into the D-cyl to generate higher concentrations of syngas. This in turn can further improve the engine thermal efficiency.

The use of early intake valve closing (EIVC) can lead to improvements in spark-ignition engine efficiency. One of the greatest barriers facing adoption of EIVC for high power-density applications is the challenge of boosting as EIVC strategies reduce volumetric efficiency. Turbochargers with variable nozzle turbines (VNT) have recently been developed for gasoline applications operating at high exhaust gas temperatures. The use of a single VNT as a boost device may provide a lower-cost option compared to two-stage boosting systems or 48 V electronic boost devices for some EIVC applications. A predictive model was created based on engine testing results from a 1.6 L turbocharged gasoline direct injection engine [1]. The model was tuned so that it predicted burn-rates and end-gas knock over an engine operating map with varying speeds, loads, compression ratios and fuel types.

Modern spark ignited engines face multiple barriers to achieving higher thermal efficiency. This study investigated the potential of utilizing both continuously variable valve actuation (VVA) and low-pressure cooled exhaust gas recirculation (EGR) to improve engine thermal efficiency at part-load conditions. Six speed / load points were investigated on a 1.6 L turbocharged gasoline direct injection engine. A design of experiment (DoE) approach using the Box-Behnken surface response model was conducted. The DoE results revealed different brake specific fuel consumption (BSFC) responses to the valve phasing and the intake valve lift at different operating conditions. Further engine testing was carried out at each speed / load point to confirm the engine efficiency and combustion performance when targeting different valvetrain controls and EGR strategies. The results indicated that utilizing the VVA system could always reduce BSFC at the studied operating conditions.

A novel approach to the Integration of Turbocompounding/WHR, Electrification and Supercharging technologies (ITES) to reduce fuel consumption in a medium heavy-duty diesel engine was previously published by FEV. This paper describes a modified approach to ITES to reduce fuel consumption on a heavy-duty diesel engine applied in a Class 8 tractor. The original implementation of the ITES incorporated a turbocompound turbine as the means for waste heat recovery. In this new approach, the turbocompound unit connected to the sun gear of the planetary gear set has been replaced by an organic Rankine cycle (ORC) turbine expander. The secondary compressor and the electric motor-generator are connected to the ring gear and the carrier gear respectively. The ITES unit is equipped with dry clutch and band brake allowing flexibility in mechanical and electrical integration of the ORC expander, secondary compressor and electric motor-generator to the engine.

Under low-temperature combustion for the high fuel efficiency and low emissions achievement, the fuel impingement often occurs in diesel engines with direct injection especially for a short distance between the injector and piston head/cylinder wall. Spray impingement plays an important role in the mixing-controlled combustion phase since it affects the air-fuel mixing rate through the disrupted event by the impingement. However, the degree of air entrainment into the spray is hard to be directly evaluated. Since the high spray expansion rate could allow more opportunity for fuel to mix with air, in this study, the expansion rate of impinged flame is quantified and compared with the spray expansion rate under non-vaporizing conditions. The experiments were conducted in a constant volume combustion chamber with an ambient density of 22.8 kg/m3 and the injection pressure of 150 MPa.