Cyclic Combustion Variability of Dimethyl-Ether-Fueled Agricultural Tractor Engine

Internal combustion engines (ICEs) are one of the greatest inventions ever. They dramatically changed access and freedom of movement for humans and goods over long distances. ICEs have remained the most preferred choice of transportation technology in the last 130 years despite presence of electric motors and steam engine-based transportation technologies [1]. Spark ignition (SI) and compression ignition (CI) engines dominate the market over these transportation technologies due to their lower cost, longer range, comfort, convenience, and higher power density. However, worldwide, the marine, air, and road transportation sectors release ∼10–15% of greenhouse gas (GHGs) emissions [2]. Emissions from gasoline and diesel engines, on one side harm human health and on the other side, are responsible for increasing the earth’s surface temperature to a certain extent [3]. These hazardous emissions can be reduced by using carbon-neutral alternative fuels and advanced engine/combustion technologies [4–7]. These popular alternative fuels include hydrogen (H₂), methanol (CH₃OH), and dimethyl-ether (CH₃–O–CH₃), as realized by policymakers for the CI engine-powered transport segment lately [8]. The most significant fuel properties, namely the cetane number (CN) (diesel, 40–55; dimethyl ether (DME): ≥ 55), ignition temperature, boiling point, and surface tension, suggest the superiority of DME over conventional diesel [9]. It has a lower autoignition temperature than baseline diesel; however, it depends on atmospheric conditions. DME has a higher autoignition temperature than baseline diesel (diesel, 250 °C; DME, 350 °C), but at higher pressures, its auto-ignition termerature is lower (between 200 and 250 °C), offering advantages [10–13]. Higher CN of DME leads to a lower ignition delay, thereby a shorter premixed combustion period than baseline diesel. Lower C–O bond energy (359.0 kJ/mol) than C–H (410.4 kJ/mol) plays a vital role in combustion [14,15]. Hence, the C–O bond breaks faster than the C–H bond. DME also has a lower C/H ratio, which leads to a shorter ignition delay and higher CN [16]. DME has 34.8% (w/w) oxygen, which promotes combustion and helps reduce the formation of particulate matter (PM) [17]. Also, the presence of an oxygen atom and the absence of a C–C bond in the DME molecule lead to soot-less combustion [18]. DME’s lower heating value (LHV) is approximately two-thirds of baseline diesel (DME, 28.43 MJ/kg; diesel, 42.5 MJ/kg), necessitating a higher DME quantity supply to produce the same engine power output. The stoichiometric A/F ratio for DME is 8.98 kg-air/kg, which is much lower than conventional diesel (14.6 kg-air/kg). Higher latent heat of vaporization of DME (460 kJ/kg at −20 °C) compared to baseline diesel (250 kJ/kg at normal temperature and pressure (NTP)) helps reduce NO_x emissions due to lower in-cylinder temperatures for DME because DME spray absorbs more heat from the cylinder contents during evaporation. Sahu and Srivatsava [19] reported that DME spray combustion showed dominant premixed combustion, whereas n-heptane spray combustion showed intense mixing-controlled combustion. During an initial simulation study, the authors verified near-zero soot emissions from the virtual engine operation using existing and modified fuel injection systems [20].

Substantial cyclic variations arise due to combustion variations in consecutive engine cycles and variations in the heat release as well as pressure developed in each cylinder of a multi-cylinder engine. These cyclic variations are responsible for power and thermal efficiency losses, higher emissions, and engine noise. The study of cyclic variations is essential since their extremes determine engine operating limits. Engine fuel requirement is dictated by faster burning cycles, while slower burning cycles lead to incomplete combustion, lesser efficiency, reduced performance, and increased emissions. These cyclic variations lead to brake torque variations, affecting the vehicle drivability [21]. Four main factors responsible for cyclic variations are variations in (i) charge composition, (ii) cyclic cylinder charging, (iii) in-cylinder charge motion, and (iv) mixing of fresh charge with residual gases from the previous cycles. Spray direction in the combustion chamber during compression stroke affects the cyclic variations, affecting the engine performance at low speeds and loads [22]. Cyclic variations are lower in a diesel engine than in a SI engine; however, they are significant and have a major impact on the engine performance and emissions.

The factors responsible for cyclic variations could vary among the SI, dual-fuel, flex-fuel, and homogeneous charge compression ignition (HCCI) engines. For diesel engines, cyclic variations determine the combustion stability; hence, researchers try to understand the impact of alternative fuels on combustion stability. Several researchers reported that cyclic variations originate from the high dimensional stochastic effects in the investigated cycles and the low dimensional deterministic effects from the previous cycles [23–25]. Zhang et al. [26] recommended studying in-cylinder flows to understand the cyclic variations in diesel engines. Singh et al. [25,27] investigated cyclic variations in reactivity-controlled compression ignition (RCCI) engines by varying the injection timings and understanding the bifurcation for cyclic combustion. Maurya and Agarwal [28] reported an increase in the coefficient of variation (COV) of P_max (<3%) with increasingly richer charge and inlet air temperature for an HCCI engine. However, the COV_IMEP exceeded the 10% limit, representing the possibility of drivability issues. Zhong et al. [29] studied various combustion parameters to understand cyclic variations and correlated them with the variations in the injection rate of a common rail direct injection (CRDI) diesel engine. Kouremenos et al. [30] and Rakopoulos et al. [31] used stochastic analysis techniques to understand cyclic variations in diesel engines. Kouremenos et al. [30] indicated that injection timing and delay did not play any role in cyclic variations of maximum pressure (P_max). Wang et al. [32] studied cyclic variations of DME while adopting the premixed charge compression ignition (PCCI) combustion approach by injecting DME into the port in varying quantities. They found an increase in COV of P_max with increasing DME quantity at a constant speed. Hou et al. [33] reported that peak in-cylinder pressure and temperature increased when the engine was about to experience knocking in DME-fueled HCCI engine.

Very few studies have been reported in the open literature on the cyclic variations of DME-fueled engines. This investigation aimed to understand the cyclic combustion variability of a 100% DME-fueled engine by comparing it with a conventional diesel engine. An unmodified diesel engine and a modified DME engine were used for this investigation. DME engine modifications included injector modifications and a 1.33 times peak pressure fuel pump compared to the baseline diesel fuel pump, fed by an upstream pneumatic feed pump that pressurized DME up to 70 bar to prevent vapor lock in the fuel lines. Parameters derived from in-cylinder pressure, such as maximum in-cylinder pressure (P_max), maximum heat release rate (HRR_max), and the maximum rate of pressure rise (ROPR_max), were taken as the main combustion stability parameter to assess the cyclic variability of the DME-fueled engine vis-à-vis diesel-fueled engine. Statistical analysis was used to find the frequency distribution of various parameters to assess the maximum repeatability of the same value. The COV was then calculated to assess the engine stability based on the variability of different combustion parameters.

This study used two test fuels with distinct physiochemical properties, namely: DME and mineral diesel. Diesel was procured from local fuel station (Indian Oil Corporation Limited) and was BS-VI compliant. DME was imported from Korea. The physicochemical properties of DME and baseline diesel used in this experiment are given in Table 1.

A three-cylinder, water-cooled, four-stroke tractor test engine was coupled to a transient dynamometer, as shown in Figs. 1 and 2, to conduct the experiments. Specifications of the test engine are given in Table 2. The test engine was coupled to the dynamometer via a drive-in assembly equipped with rubber coupling, which absorbs the vibrations and make the engine loading smoother. A throttle controller operates the fuel pump throttle to regulate the fuel quantity injected according to the engine load and speed. A precision torque flange was installed between the transient dynamometer shaft and the driveline assembly to measure the engine torque output accurately.

The parameters considered to assess cyclic variations in diesel and DME were maximum in-cylinder pressure (P_max), RoPR_max, HRR_max, crank angle position at which P_max occurred (°CA P_max), crank angle position at which RoPR_max occurred (°CA RoPR_max), crank angle position at which HRR_max occurred (°CA HRR_max), indicated mean effective pressure (IMEP), and coefficient of variation (COV) of different parameters.

In-cylinder combustion of DME is an oxidation reaction, which depends on the fuel quantity injected, and temperature, and pressure the fuel combustion creates. DME (CH₃OCH₃), upon reaction with oxygen, first produces CH₃OCH₂, which is further oxidizes to form CH₃OCH₂OO, which gets converted to CH₂OCH₂OOH, and finally, CH₃, CH₃O, CH₂O, and OH radicals are generated [34]. The combustion chamber is subjected to the dynamic movement of engine parts. Therefore, cyclic variations always exist. These combustion parameters are discussed section-wise as follows: (i) variations in the COV of P_max and IMEP, (ii) cyclic variations in P_max, (iii) cyclic variations in ROPR_max, (iv) cyclic variations in HRR_max, and (v) cyclic variations in IMEP.

Figure 4 represents the variations of COV of P_max and IMEP for DME and mineral diesel fueled engine at varying engine speeds (1200, 1600, and 2000 rpm). The selection of P_max for describing the cyclic variations has an advantage over the maximum rate of pressure rise (RoPR_max) since it leads to larger errors in computation. Differences in the COV of P_max between DME and baseline diesel were high at 1600 rpm but low at maximum brake torque (MBT) speed (1200 rpm) and rated power speed (2000 rpm). The COVs of P_max were higher at lower loads, comparable at medium loads, and negligible at higher loads for all tested engine speeds. These variations are acceptable and are attributed to a higher cetane number of DME than baseline diesel, leading to a shorter delay in combustion. COV_IMEP represents the overall cyclic variations since it integrates all the fluctuations during combustion and provides information about the “stability of engine combustion.”

Lower COV_IMEP indicated that the DME engine was more stable than baseline diesel engine. The variations in COV_IMEP were higher at lower loads. They became negligible at higher loads. This is attributed to lower ignition delay at higher loads since it reduces accumulated fuel in the cylinder, injected between the start of injection and the ignition initiation. Negligible differences in the COV_IMEP of diesel and DME represent the suitability of DME fueling at higher loads. Although the reported COV values may seem higher than small-bore engines, they would be acceptable for tractor-engine operation. Kim et al. [35] reported increasing and decreasing trends in COV_IMEP of DME with respect to baseline diesel. In this study, three loads (1.29, 3.88, and 6.47 bar BMEP), corresponding to 34, 102, and 170 Nm torque representing low, medium, and high load conditions at 2000 rpm for diesel and DME, are compared.

P_max is an important combustion parameter in engine design and calibration [21,36]. The relationship between combustion and variations in the in-cylinder pressure is complex. Figure 5 shows the P_max with respect to combustion cycles for DME (right column) and diesel (left column) at three loads (1.29, 3.88, and 6.47 bar BMEP).

The mean value of P_max for 250 combustion cycles for diesel and DME is represented by lines in Fig. 5. At low load (1.29 bar BMEP), P_max showed a wavy pattern for diesel, which had significant deviations from the trend seen for DME. The mean P_max was lower for baseline diesel. The wavy pattern suggested that the later cycles deviated from the P_max trend compared to the former cycles and were scattered on both the upper and lower sides of the mean P_max at regular intervals. For diesel, the P_max showed significant deviations from the mean P_max (45.2 bar), with values ranging between 40 and 48 bar. For DME, this deviation was limited to ∼1.1 bar around the mean P_max (48.2 bar). DME showed scattered distribution much closer to the mean P_max.

P_max variations were lower for diesel and DME at an intermediate BMEP of 3.88 bar; however, the absolute values were lower for DME than baseline diesel. This can be attributed to DME’s higher injected fuel mass with increasing load, which caused ignition delay and reduced the P_max. In addition, DME had a higher latent heat of vaporization, which further reduced the P_max. At a high load (6.47 bar BMEP), cyclic variations of P_max were higher for diesel than DME, especially in the first 100 cycles, where the deviations were more significant and lower than the mean value. This behavior in the initial cycles indicates the possibility of engine hunting due to occasional knocking, which was not the case for DME. The inherent fuel oxygen in the molecular structure of DME plays a vital role in combustion. However, DME properties such as lower surface tension, viscosity, and boiling point lead to superior spray in the combustion chamber. This leads to a more uniform air–fuel mixture formation at high loads. The standard deviation of P_max was 0.7–1.4 bar for diesel and 0.7–0.8 bar for DME, suggesting lower fluctuations in P_max for DME engines than baseline diesel engines.

Besides evaluating the cyclic variations of P_max, understanding the °CA P_max is also essential. It should be closer to the top dead center (TDC) to achieve the maximum thermal efficiency. An optimum crank angle position of P_max is vital since the power produced by the engine deteriorates if it is too far from the TDC or too near to the TDC. Figure 6 shows the interdependency of the P_max and the °CA P_max.

Figure 6 shows the P_max distribution along the crank angle position for diesel and DME. The crank angle position of P_max for DME was nearly constant from lower to medium engine loads and slightly retarded at higher engine loads. However, the crank angle position of P_max for baseline diesel retarded with increasing load and was more scattered at high engine load (6.47 bar BMEP). In other words, the repeatability of the °CA _Pmax was higher for DME and very low for baseline diesel. The P_max was less scattered for diesel and DME at low and medium loads. But at high loads, P_max was quite scattered for baseline diesel. In addition, P_max shifted away from the TDC more progressively with increasing engine load for diesel than DME. A single cluster of P_max with crank angle position was observed for DME at all loads; however, two distinct clusters were observed for baseline diesel at high load (6.47 bar BMEP). This indicated that DME combustion was more stable than baseline diesel at all loads, and more so at high loads. At 1.29 bar BMEP, P_max occurred near TDC between 0–3 CAD for diesel and 7–11 CAD for DME. Huang et al. [12] and Longbao et al. [37] also reported °CA P_max farther away from TDC for DME than baseline diesel. Figure 7 shows the frequency distribution of P_max for diesel and DME. It represents the repeatability of the same value over different combustion cycles. The frequency distribution of P_max for DME was higher than baseline diesel, i.e., P_max had significantly higher repeatability.

At 1.29 bar BMEP, P_max varied from 42–48 bar (14% repeatability of the same value) and 45–50 bar (∼28.8% repeatability of the same value) for baseline diesel and DME, respectively. The maximum repeatable P_max were 44.5 and 48 bars for baseline diesel and DME, respectively. DME showed higher repeatability for combustion cycles than baseline diesel. At 3.88 bar BMEP, P_max varied between 51.5–56 bar (26.4% repeatability for the same value) for baseline diesel and 45.5–49 bar (25.6% repeatability for the same value) for DME. 53.5 bar and 47 bar were the maximum P_max values for diesel and DME, respectively, for which the maximum repeatability was observed over the recorded combustion cycles. At high load (6.47 bar BMEP), P_max for diesel varied from 52–61 bar, with maximum repeatability of the same value being 31.6%. For DME, P_max varied from 46.5 to 50.5 bar, with maximum repeatability of the same value being 23.6%. For diesel and DME, the P_max values were 56 and 49 bar, respectively, showing maximum repeatability. In the case of baseline diesel, the trend of maximum P_max repeatability of the same value was in increasing order, i.e., 14–26.4–31.6%, but it was in decreasing order for DME, i.e., 28.8–25.6–23.6%. Although more than two clusters were formed for diesel at high load (6.47 bar BMEP), the repeatability of the same value was higher than DME. It showed that an emsamble of combustion cycles provided the same P_max, but the rest of the cycles deviated from this maximum repeatable value.

The variations in RoPR_max are directly related to combustion noise. It is a critical parameter to judge cyclic variations in the engines.

At low load (1.29 bar BMEP), the scattering of RoPR_max was higher for DME than baseline diesel, as shown in Fig. 8. Also, the mean RoPR_max was ∼70.3% higher for DME, indicating that the pressure increase per crank angle degree was higher. This showed the possibility of a higher mechanical impact on the engine components at this load. At medium load (3.88 bar BMEP), the scattering of RoPR_max was lower for DME than baseline diesel, indicating lower cyclic variations. The mean RoPR_max of baseline diesel was ∼ 26.3% lower than DME, an opposite trend of lower load condition (1.29 bar BMEP). Similar behavior was seen at a high load (6.47 bar BMEP), where the mean RoPR_max was ∼16.5% lower for DME than baseline diesel. In summary, the scattering of RoPR_max was higher for DME at a lower load than baseline diesel and was lower for DME at medium and high loads than baseline diesel. DME fueling provided superior combustion characteristics over baseline diesel as the engine load increased from low-to-high. During the experiments, the engine could not start directly in idling, and a manual throttle pulling to 100% open position started the engine smoothly. The issues in starting the engine with DME at idling/ low load were possibly responsible for higher cyclic variations in RoPR_max at low load than baseline diesel.

The standard deviation of ROPR_max was 0.8–3.5 bar/deg for baseline diesel and 1.9–2.4 bar/deg for DME, suggest lower fluctuations in the DME engine. According to Wang et al. [32], the cyclic variations of ROPR_max roughly indicate the variations in HRR_max, although RoPR is sensitive to combustion noise. Therefore, the °CA RoPR_max is sometimes used to estimate the combustion phasing. The RoPR_max vs CAD scatter for 250 combustion cycles was plotted to analyze the cyclic variations, as shown in Fig. 9.

At a low load (1.29 bar BMEP), the RoPR_max was more scattered in a wider range for DME. Also, RoPR_max was distributed in a narrower range of °CA RoPR_max for baseline diesel than DME. Two distinct clusters of RoPR_max are seen in Fig. 9 for both test fuels at all loads. It also indicated that the repetition of the same RoPR_max was higher in baseline diesel than in DME. This gives more credibility to the claim that cyclic variations were higher for baseline diesel than DME. DME showed lower cyclic variations for intermediate (3.88 bar BMEP) and high (6.47 bar BMEP) loads than diesel. This was due to two distinct observations from Fig. 9: (i) RoPR_max was scattered in a smaller range for DME, and (ii) ROPR_max occurred in a narrower range for DME. Only one cluster occurred for DME at a high load (6.47 bar BMEP), and only ∼10 combustion cycles were outside the cluster. This suggested that DME exhibited reduced cyclic variations as engine operation moved from low-to-high loads. However, it was an opposite trend for diesel fueling; wherein the engine showed higher cyclic variations as it moved from low-to-high loads. Therefore, DME fueling showed superior combustion characteristics than baseline diesel at intermediate and high loads. However, a more robust recommendation could be given by analyzing the frequency distribution of RoPR_max, plotted in a histogram shown in Fig. 10.

Figure 10 shows the frequency distribution of combustion cycles for RoPR_max. The combustion cycle frequency of RoPR_max decreased with increasing engine load for baseline diesel. However, for DME, it increased. At 1.29 and 3.88 bar BMEP, the maximum repeated RoPR_max for baseline diesel was 6 and 14 bar/deg, respectively, whereas it was 9 bar/deg for DME under corresponding load conditions. At 6.47 bar BMEP, repeated RoPR_max for baseline diesel and DME were 11 (18% repeatability) and 10 bar/deg (22% repeatability), respectively. It indicated that DME’s combustion characteristics were superior to baseline diesel as the engine moved from low-to-high loads. It indicated that DME exhibited lower cyclic variations over diesel at intermediate and high loads, based on ROPR_max.

Heat release rate (HRR) indicates how quickly the chemical energy of the fuel is released during combustion, and it affects the engine power output [21]. HRR variations for any fuel indicate whether engine operation is smooth or unstable [32].

Figure 11 shows HRR_max (J/°CA) variations in 250 consecutive engine combustion cycles for baseline diesel and DME. At low (1.29 bar BMEP), intermediate (3.88 bar BMEP), and high (6.47 bar BMEP) loads, HRR_max exhibited a narrower scatter for DME than baseline diesel. The mean HRR_max for DME was lower than the mean HRR_max for baseline diesel. This could be due to longer injection of increased DME quantity combustion over a longer time, leading to lower HRR, particularly during the premixed combustion phase due to higher cetane number of DME. The trend for mean HRR_max for diesel and DME were different, i.e., (HRR_max Mean)_{1.29 bar BMEP} < (HRR_max Mean)_{3.88 bar BMEP} > (HRR_max Mean)_{6.47 bar BMEP} and (HRR_max Mean)_{1.29 bar BMEP} > (HRR_max Mean)_{3.88 bar BMEP} > (HRR_max Mean)_{6.47 bar BMEP}. Overall, the cyclic variations for DME were lower than baseline diesel. The standard deviation of HRR_max was 4.5–7.1 J/°CA for baseline diesel and 4.1–4.6 J/°CA for DME. However, the trends of HRR_max with respect to °CA HRR_max also need to be analyzed for judging the cyclic variations, as shown in Fig. 12.

It can be seen from Fig. 12 that HRR_max variations with crank angle, DME exhibited fewer variations than baseline diesel at 1.29 and 3.88 bar BMEP. Diesel variations were distributed in a narrower crank angle range but larger magnitudes than DME. Both test fuels exhibited single cluster at low and medium loads. A similar pattern was observed for high loads, albeit two clusters for both test fuels. These observations also indicated fewer cyclic variations for DME compared to baseline diesel. The most critical observations can be made from the frequency distribution data presented in Fig. 13.

The maximum frequency of HRR_max was lower for DME than baseline diesel at low and medium engine loads. However, it was higher at high engine loads. At 1.29 bar BMEP, diesel and DME showed variations in HRR_max from 70–110 and 60–86 J/°CA, with maximum repeatability of 85 and 70 J/°CA. HRR_max increased and varied from 105–145 J/°CA, with maximum repeatability of 48% for 120 J/°CA for baseline diesel and varied from 60–84 J/°CA with maximum repeatability of 17.2% for 72 J/°CA HRR_max for DME, at 3.88 bar BMEP. At 6.47 bar BMEP, HRR_max decreased for baseline diesel and increased for DME compared to medium load. HRR_max varied from 76–102 J/°CA for baseline diesel and 66–92 J/°CA for DME. The maximum repeatability of the same value for baseline diesel was 16.4% and 22.4% for DME.

Drivability remains a vital parameter the end customer uses to judge a vehicles made by the original equipment manufacturers (OEMs). Hence, OEMs use cyclic variability of various vital combustion parameters before accepting to use of any alternative fuel in the existing/modified engines. It is accepted universally that drivability issues arise if COV_IMEP is >10% [21].

Cyclic variations in IMEP over 250 consecutive combustion cycles for baseline diesel and DME are shown in Fig. 14. IMEP variations showed fluctuations over a broad range for both test fuels. DME showed lower IMEP variations than baseline diesel (36.21, 24.8, and 0.9% lower at 1.29, 3.88, and 6.47 bar BMEP). DME showed lower IMEP than baseline diesel without creating any significant drivability issues. Further, the frequency distribution of IMEP is shown in Fig. 15.

At low load (1.29 bar BMEP), IMEP was 2.85–3.55 bar for baseline diesel, and the corresponding values were 1.7–2.1 bar for DME. This range increased at medium load (3.88 bar BMEP) to 5.6–6.25 bar for baseline diesel and 4.25–4.7 bar for DME. It increased at high load (6.47 bar BMEP) to 8.3–9.0 bar for baseline diesel and 8.2–8.8 bar for DME. The repeatability of IMEP values was almost similar for both test fuels.

Cyclic variations for DME and baseline diesel combustion engines were investigated for a three-cylinder tractor engine, which used a modified fuel injection system for 100% DME injection. Variations in various combustion parameters for DME and baseline diesel were assessed in this study. The cyclic variations in the combustion parameters were calculated from the in-cylinder pressure data for 250 consecutive engine cycles acquired at 1200, 1600, and 2000 rpm engine speeds at No Load, 1.29, 2.59, 3.88, 5.18, and 6.47 bar BMEP. The diesel engine was tested using existing fuel pump and mechanical injectors. In contrast, this study used a modified fuel injection pump (1.33 times higher pressure) and modified injectors of higher nozzle hole diameter for DME induction. Mean P_max was lower for DME than baseline diesel at 3.88 and 6.47 bar BMEP but was higher at 1.29 bar BMEP. Overall, the COV of P_max was higher for baseline diesel than DME at 1600 rpm at all loads. However an opposite trend was observed at 1200 rpm. Mean RoPR_max and its variations were higher for DME than baseline diesel at low load (1.29 bar BMEP) but lower at medium and high loads (3.88 and 6.47 bar BMEP). The repeatability of RoPR_max was lower for baseline diesel and it increased from low-to-high load sweep. At high load (6.47 bar BMEP), only one distribution cluster was observed for °CA RoPR_max for DME, while two distribution clusters were observed for baseline diesel and DME at low and medium loads. Mean HRR_max and cyclic variations were lower for DME than baseline diesel. HRR_max and IMEP were higher for baseline diesel than DME. No conclusive trend was observed from the statistical analysis of frequency distribution. DME fueling resulted in higher COV_IMEP than baseline diesel at low and medium loads and comparable at high loads. In summary, DME combustion was smoother and showed fewer cyclic variations than baseline diesel. However, the combustion parameters such as P_max and HRR_max were lower for DME because of their physicochemical properties.

The authors acknowledge the Science and Engineering Research Board (SERB), Department of Science and Technology (DST), Government of India (Sanction Number IMP/2019/000245 dated 22–01-2020) for funding the project entitled “Ultra-clean emissions DME-fueled tractor-engine prototype development for agricultural applications,” for collaboration between Engine Research Laboratory (ERL), Indian Institute of Technology Kanpur (IITK) and TAFE Motors and Tractors Limited (TMTL), Alwar. The authors acknowledge the J C Bose Fellowship by SERB, Government of India (Grant EMR/2019/000920) and SBI endowed Chair from the State Bank of India to Professor Avinash Kumar Agarwal, which enabled this work. Sh Hemant Kumar’s efforts are gratefully acknowledged for his assistance in building the experimental setup. The help extended by Roshan Lal, Surendra Kumar, Ayush Tripathi, Sam Joe, Rahul Kumar Singh, Krishna Chandra, and Vivek in performing the experiments is gratefully acknowledged. Hari Om Sharma and Sanjeev Kumar from TMTL are acknowledged for ensuring part availability and assisting in engine testing.

There are no conflicts of interest. This article does not include research in which human participants were involved. Informed consent is not applicable. This article does not include any research in which animal participants were involved.

The data sets generated and supporting the findings of this article are obtainable from the corresponding author upon reasonable request.

BEVs =

battery electric vehicles

BMEP =

brake mean effective pressure

CAD =

crank angle degrees

CI =

compression ignition

CN =

cetane number

COV =

coefficient of variation

DME =

dimethyl-ether

GHG =

greenhouse gas

HCCI =

homogeneous charge compression ignition

HRR =

heat release rate

ICE =

internal combustion engine

IMEP =

indicated mean effective pressure

LHV =

lower heating value

OEM =

original equipment manufacturer

PM =

particulate matter

RCCI =

reactivity-controlled compression ignition

RoPR =

rate of pressure rise

RV =

repetition of value

SI =

spark ignition

TDC =

top dead center